Dissertations / Theses on the topic 'Rails steel'

This thesis presents the results of experimental and numerical investigations carried out to assess the effects of tube bending and hydroforming on the crash performance of s-rail structures manufactured from three different advanced high strength steels, namely DDQ, HSLA350, and DP600. The main impetus for this project is to reduce vehicle weight through material substitution and, in order to do so, the effects of material strength on crashworthiness, as well as the interaction between forming processes and crash response must be well understood. To this end, in the current research, s-rails were fabricated through tube bending and hydroforming experiments conducted on DDQ, HSLA350, and DP600 steels with a nominal wall thickness of 1. 8mm, as well as HSLA350 steel with a nominal wall thickness of 1. 5mm. Impact experiments were subsequently performed on non-hydroformed and hydroformed s-rails to examine the effects of the forming processes and material substitution on the crushing loads and levels of absorbed energy. All forming and crash experiments were simulated using numerical finite element methods which provide additional insight into various aspects of the crash response of these structures. In particular, crash simulations were used to show the effects of work-hardening, material thickness changes, and residual stresses incurred during the forming operations.

The numerical tube bending simulations accurately predict the results of the tube bending and hydroforming processes for all materials, particularly for the DP600; the predictions for the DDQ material are the least accurate. Both simulations and experiments show that material thinning occurs on the tensile side of the bend, and material thickening on the compressive side of the bend; the level of thickness change is unaffected by material strength or initial material thickness. The low-pressure hydroforming process does not greatly affect the thickness and strain distributions of s-rails.

The crash simulations provide predictions that are in excellent accord with the measured results, with a maximum error of ±10% in the peak loads and energies; simulations of DP600 s-rails are the most accurate, while simulations of DDQ s-rails are the least accurate. Through simulations and experiments, it is shown that material thickness has the greatest effect on the crash performance of s-rail structures, while material strength plays a secondary role. A 20% increase in the wall thickness of HSLA350 s-rails amounts to a 47% increase in energy absorption. Substituting HSLA350 and DP600 steels in place of DDQ steel leads to increases in energy absorption of 31% and 64%, respectively, for corresponding increases in strength of 30% and 76%. Neglecting material strain-rate effects in the numerical models lowers the predicted peak loads and energies by roughly 15%. By performing a numerical parametric study, it is determined that a weight reduction of 22% is possible by substituting thinner-gauge DP600 s-rails in place of DDQ s-rails while maintaining the energy absorption of the structures.

Etude de la diffusion et de la perméation a l'hydrogène dans différentes nuances d'aciers à rail en fonction de la teneur en soufre, du sens de prélèvement des éprouvettes et du taux de corroyage. Étude de la fragilisation différée sur une nuance dure par suivi de l'émission acoustique en fonction du chargement en hydrogène. Examen de l'influence de l'hydrogène sur le comportement en traction des différentes nuances

Este estudo analisou, em um primeiro momento, soldas de trilhos perlíticos para carga pesada soldados pelo processo aluminotérmico e solda topo com centelhamento (Flash butt-weld) focando nas alterações macro e microestruturais, bem como alterações de dureza decorrentes do processo. Uma junta em situação de uso real também foi estudada comparando-se o comportamento de deformação e desgaste à condição sem uso. Todos os casos apresentaram comportamento semelhante na zona afetada pelo calor possuindo perda de dureza em região de microestrutura esferoidizada. A origem desta estrutura foi, então, discutida. A formação de esferoidização pelo fenômeno de redução de energia de interface por movimentação de interfaces sólidas é considerado incompatível com os tempos dos processos utilizados. A hipótese de formação da zona esferoidizada por transformação do eutetóide divorciado (Divorced Eutectoid Transformation, DET) foi testada por meio de simulações de ciclos térmicos em dilatômetro de têmpera, para três diferentes aços. Com base nos resultados é seguro afirmar que o processo envolvido na esferoidização ao final da zona afetada pelo calor de trilhos perlíticos soldados é, de fato, a transformação do eutetóide divorciado. Confirmando esta hipótese, observa-se que o aumento do teor de carbono nos trilhos aumenta a faixa de esferoidização.
This work analyzed, initially, pearlitic heavy haul rail thermite welds and flash buttwelds, focusing in macro and microstructural changes as well as hardness changes occurring due to the processes. A weld in real use was also studied comparing the deformation behavior and wear to the unused condition. All cases presented similar behavior at the heat-affected zone with hardness loss associated to a spheroidized microstructure. The mechanisms for the formation of this structure, was discussed. The spheroidization by solid interface movement, driven by interface energy reduction, is not compatible with the processing times for welding. The hypothesifs of spheroidized region formation by a divorced eutectoid transformation (DET) was tested by simulated heat-treatments using a dilatometer and three different steels. Based on that it is safe to conclude that the process for the formation of an spheroidized zone at the end of the heat-affected zone on welded pearlitic rails is, indeed, the divorced eutectoid transformation. Furthermore, the carbon content was shown to increase spheroidization range.

Les rails de Chemins de fer sont soumis à de la fatigue de roulement due au passage répété des roues de train, ce qui induit différents types de fissures, telles que les Squats. Ces fissures sont soumises à un chargement de mode mixte non-proportionnel I + II + III, dans des proportions variables le long du front, avec des phases de compression, ce qui rend la prédiction de leur trajet et de leur vitesse délicate.La cinétique de fissuration en mode I a été déterminée dans de l’acier à rail R260, pour des rapports R positifs et négatifs, ainsi que la cinétique de mode mixte II & III corrigée des effets de frottement. Les Facteurs d’Intensité des Contraintes (FICs) effectifs ont été obtenus à partir des sauts de déplacements dans le plan et hors plan mesurés en surface, le long de la fissure. De ces lois cinétiques, il ressort que ni le mode I seul, ni les modes de cisaillement seuls ne peuvent expliquer la fissuration des rails. C’est donc la combinaison des trois modes, suivant des trajets de chargement complexes, qui en est responsable.Des essais de fissuration par fatigue en mode mixte non-proportionnel I + II ont ensuite été réalisés, suivant des trajets de chargement représentatifs de ceux subis par les squats. La stéréo corrélation d’images a été utilisée pour obtenir les champs de déplacements en pointe de fissure. Les méthodes classiques de mesure des FICs à partir de champs de déplacements n’étant pas adaptées, du fait des efforts de contact et frottement entre les lèvres de fissure, de nouvelles méthodes ont été développées. Les trajets et vitesses de fissuration ont été étudiés au regard de ces FICs effectifs. Il apparait que la prédiction du trajet à partir du critère de la contrainte tangentielle maximale n’est pas très fiable, mais peut être améliorée par la prise en compte de la plasticité en pointe de fissure ainsi que des efforts de contact/frottement entre les lèvres de fissure. Les vitesses de propagation obtenues se corrélèrent bien avec une combinaison des trois FICs effectifs dans une loi de type « Paris ».De ces essais, il ressort que du fait de la rugosité de la fissure, l’enchevêtrement d’aspérités et le frottement réduisent considérablement les FICs effectifs. Et cela même en l’absence de compression normale, ce qui ne peut être modélisé par une simple loi de Coulomb. De plus, l’usure des lèvres de fissure a aussi une forte influence sur les FICs effectifs. Le challenge pour les applications structurelles est donc non seulement de choisir le critère de bifurcation et la loi cinétique les plus appropriés, mais également de prendre en compte la rugosité et l’usure des lèvres de fissure, afin d’estimer correctement les FICs effectifs à utiliser dans ces modèles.Pour les applications industrielles, une approche d’ingénieur, simplifiée, a été proposée afin de prendre en compte le frottement induit par la rugosité dans l’estimation des trajets de chargements effectifs à partir des trajets nominaux. Cette approche a été validée sur des essais de mode mixte séquentiel I + II & III
Rails are submitted to Rolling Contact Fatigue due to repeated passages of train wheels, which induces several types of cracks, such as Squat-type cracks. Those cracks undergo non-proportional mixed-mode I + II + III loading, including compression phases, in variable proportions along the crack front, making the prediction of their paths and growth rates a challenge.Mode I crack growth kinetics, for positive and negative R ratios, were first determined in R260 steel, as well as friction-corrected crack growth kinetics for fully-reversed combined mode II and III. The effective Stress Intensity Factors (SIFs) were deduced from the measured in-plane and out-of-plane crack face sliding displacements. From those kinetic laws, it was deduced that neither pure mode I, nor pure shear mode loadings can explain the crack growth rates observed in rails. A combination of those three loading modes, according to complex loading paths had thus to be prospected.Non-proportional mixed-mode I + II fatigue crack growth tests were then performed, following representative loading paths. Stereo digital image correlation was used to measure the near-tip displacement field. Post-treatment methods generally used to deduce the effective SIFs from these fields were inappropriate because of contact and friction stresses along the crack face. New methods were thus developed. The crack paths and growth rates were analyzed, using the effective SIFs. Crack path prediction by the maximum tangential stress criterion was found not to be very reliable, but substantially improved when crack tip plasticity and the presence of contact and friction stresses along the crack faces were taken into account. The measured crack growth rates correlated well with a combination of the three effective SIFs in a Paris-type law.From these experiments, it appears that due to crack face roughness, asperities interlocking and friction substantially reduce the effective SIFs, even without any normal compression, which cannot be captured by a simple Coulomb’s law. Besides, crack faces wear also has a large influence on the effective SIFs. The challenge for structural applications is thus not only to choose the most appropriate bifurcation criterion and crack growth law, but also to take crack face roughness and wear into account, in order to estimate the correct effective SIFS to use in these models.For industrial applications, a simple engineering approach was proposed to integrate roughness-induced friction in the estimation of the effective loading path from the nominal one. This approach was validated on sequential mixed-mode I + II & III experiments

Analyse de l'influence du mode de dressage et du roulement sur les caracteristiques du rail, avec une attention plus particuliere portee aux contraintes residuelles et a l'ecrouissage, etudies au moyen de la methode de diffraction x

Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: The Tubular Track (TT) railway system is a twin beam modular railway system consisting of two reinforced concrete (RC) beams on which steel rails are continuously supported. The beams are linked with galvanised steel gauge tie bars and continuously supported by soil foundations, and can be used to replace conventional sleeper and ballast railway support. The TT railway system has in the past been analysed with various analysis methods, but were found to obtain con icting results. The con icting results means that one of the analysis methods used for the analysis and design of TT railway sections is either an underestimation or overestimation of section displacements, forces, and stresses; or both methods could even be incorrect. The main emphasis of this investigation is therefore to develop and verify static and dynamic analysis methods and modeling techniques which can be used to simulate the TT railway system accurately. The results and models of the previous analyses are not explicitly investigated in this dissertation, but serve as a motivation for this investigation. The TT system is supported by several soil strata providing vertical support, but geometrically modeling the subgrade strata in the analysis models adds a high level of complexity, and is not feasible for general analysis where soil conditions are mostly unknown. The elastic foundation theory is therefore used to accurately simulate the interaction between beam and foundation and therefore su ciently simpli es the analysis models. Simpli cation of a subgrade foundation by simulating a soil sti ness supporting the TT beam is investigated and analysed by comparing nite element analysis (FEA) results of various soil models using parameters of four known soil formations currently in use at TT railway sections. The FEA of the subgrade formations indicates that there is a linear relationship between the modulus of subgrade reaction for a square plate bearing test and a rectangular, in nitely long plate representing the subgrade support for the TT beams. A square plate bearing test can therefore be performed on site and modi ed to represent the actual subgrade support sti ness of the TT railway structure, whereafter it can be used for the analysis and design of the TT system using one of the proposed analysis methods. The analysis models used range from simple theoretical models based on elastic foundation principles, to two-dimensional (2D) beam elements, and ultimately to complex three-dimensional (3D) solid nite element models. The models used for the analyses are the Single and Double Beam elastic foundation, PROKON 2D beams, ABAQUS 2D beams and ABAQUS 3D solid element models. The alternative analysis methods considered should provide a clear indication of which analysis methods are accurate and feasible for design of the TT system. An in-situ reference model with known de ections and design parameters speci c to a TT railway section is used to analyse the di erent analysis methods' accuracy and validity. The Double Beam, ABAQUS 2D and ABAQUS 3D models were found to provide very similar displacements, bending moments and shear forces for a static analysis, whereas the PROKON and Single Beam models provide unsatisfactory results. The PROKON beam model underestimates the bending moments and shear forces in the rail, and overestimates bending moments and shear forces in the RC beam by a considerably margin. This result can lead to the underdesigning of the rail which could possibly force the RC beam to be subjected to larger maximum bending moments and shear forces than for what it was originally designed for, thereby nullifying or possibly even exceeding the amount for which it was overdesigned. This e ectively accelerates material fatigue, which might be the possible cause of the small cracks in the RC beams which have been found on some TT railway sections, which is currently being investigated. A graphical user interface of the Double Beam method is provided for quick and e cient analysis. Empirical methods used to simulate the dynamic nature of a railway system are often used in the industry to simplify the dynamic loading by determining a dynamic amplitude factor (DAF) to be applied to a static load. An implicit dynamic FEA is therefore performed to obtain the DAF for the reference section, which is subsequently used for the comparison with in-situ de ection results. The results of dynamic analysis validates the proposed empirical analysis method, as the displacements obtained were very similar to actual eld test results, thereby also verifying the accuracy of the proposed analysis methods. The sensitivity of the TT system to design parameters is also investigated to indicate to which parameters the design is sensitive to and where small variations of these parameters require due consideration for future and analysis of the TT railway system.
AFRIKAANSE OPSOMMING: Die Tubular Track (TT) spoorweg stelsel is 'n dubbel balk modulêre treinspoor sisteem bestaande uit twee gewapende beton balke waarop staal spore voortdurend ondersteun word. Die balke word gekoppel deur gegalvaniseerde staal stawe vir laterale styfheid en word deurlopend ondersteun deur grond fondamente, en kan gebruik word om konvensionele dwarslêer en ballast spoorweg ondersteuning te vervang. Die TT spoorweg stelsel was in die verlede met verskeie analiseringsmetodes ontleed, maar het teenstrydige resultate gewerf. Die teenstrydige resultate beteken dat een van die analise metodes wat gebruik word vir die analisering en ontwerp van TT spoorweg seksies 'n onderskatting of oorskatting van verplasings, kragte, en spannings is; of beide metodes kan selfs verkeerd wees. Die hoofklem van hierdie ondersoek is dus die ontwikkeling en veri kasie van statiese en dinamiese analitiese metodes en modellering tegnieke wat gebruik kan word om die TT spoorweg stelsel akkuraat te simuleer. Die resultate en modelle van die vorige ontledings word nie uitdruklik in hierdie proefskrif ondersoek nie, maar dien as 'n motivering van hierdie ondersoek. Die TT stelsel word ondersteun deur verskeie grond strata wat vertikale ondersteuning verskaf, maar meetkundige modellering van die grond strata in die ontledingsmodelle veroorsaak 'n hoë vlak van kompleksiteit wat nie bruikbaar is vir algemene analises waar grondeienskappe meestal onbekend is. Die elastiese fondament teorie word daarom gebruik om die interaksie tussen die balk en die fondament akkuraat te simuleer, en vereenvoudig dus die analitiese modelle voldoende. Vereenvoudiging van 'n grond fondament deur 'n grond styfheid ondersteuning van die TT balk te simuleer is ondersoek en ontleed deur die resultate van eindige element analises van verskillende grond modelle te vergelyk. Bekende ontwerp parameters van vier bekend grondformasies wat tans gebruik word by TT spoorweg seksies word vir hierdie analises gebruik. Die eindige element analises van die grondformasies dui daarop aan dat daar 'n lineêre verwantskap tussen die modulus van grond reaksie vir 'n vierkantige plaat dratoets en 'n reghoekige, oneindige lang plaat dratoets bestaan. 'n Vierkantige plaat dratoets kan dus op terrein uitgevoer en aangepas word om die werklike styfheid van die grond ondersteuning van die TT spoorweg sisteem voor te stel. Die analitiese modelle wat gebruik word wissel van eenvoudige teoretiese modelle wat gebaseer is op elastiese fondament beginsels, twee-dimensionele (2D) balk elemente, asook komplekse driedimensionele (3D) soliede eindige element modelle. Die modelle wat gebruik is vir die ondersoek is die Enkel en Dubbel Balk elastiese fondament, PROKON 2D balke, ABAQUS 2D balke en ABAQUS 3D soliede element modelle. Hierdie reeks bied 'n duidelike aanduiding watter analiseringsmetodes akkuraat en haalbaar is vir die ontwerp van die TT stelsel. 'n In-situ verwysingsmodel met bekende de eksies en ontwerp parameters wat spesi ek is vir 'n TT spoorweg seksie word gebruik om die akkuraatheid en geldigheid van die verskillende analitiese metodes te analiseer. Die Dubbel Balk, ABAQUS 2D en ABAQUS 3D modelle verkry baie soortgelyke verplasings, buigmomente en skuifkragte vir 'n statiese analise, terwyl die PROKON en Enkel Balk modelle onbevredigende resultate verkry. Die PROKON model onderskat die maksimum buigmomente en skuifkragte in die staal spoor, en oorskat buigmomente en skuifkragte in die gewapende beton balk. Hierdie resultaat kan moontlik lei tot die onderontwerp van die staal spoor en dwing moontlik vir die gewapende beton balk om blootgestel te word aan groter buigmomente en skuifkragte as vir wat dit oorspronklik ontwerp is, en verontagsaam sodoende moontlik die kragte waarvoor dit oorontwerp is. Dit versnel e ektief materiaal vermoeiing, wat die moontlike oorsaak is van die klein krake wat gevind is in die gewapende beton balke op sommige TT spoorweg seksies wat tans ondersoek word. 'n Gra ese gebruikerskoppelvlak van die Dubbel Balk model is verskaf vir vinnige en doeltre ende ontleding. Empiriese metodes om die dinamiese aard van 'n spoorweg-stelsel te simuleer word dikwels gebruik in die bedryf om dinamiese belasting te vereenvoudig deur middel van die gebruik van 'n dinamiese amplitude faktor (DAF) wat op 'n statiese belasting aangewend word. 'n Implisiete dinamiese eindige element analise word dus uitgevoer om die DAF te ondersoek, wat daarna gebruik word vir die vergelyking met die in-situ de eksie resultate van die in-situ verwysingsmodel. Die resultate van die dinamiese analise bevestig dat die voorgestelde empiriese analise metode gebruik kan word, omdat die verplasings wat verkry baie soortgelyk was aan werklike veld toets resultate, en daardeur ook die veri ëring van die akkuraatheid van die voorgestelde analise metodes bewerkstellig. Die sensitiwiteit van die TT stelsel vir ontwerp parameters word ook ondersoek om aan te dui watter parameters die ontwerp voor sensitief is, en waar klein variasie in hierdie ontwerp parameters behoorlike oorweging vereis vir die toekomstige analisering en ontwerp van die TT spoorweg stelsel.

The worldwide preferred method for rail joining is welding; flash butt welding (FBW) and thermite welding (TW) are the two main welding methods used for joining continuous welded rail (CWR) tracks. However, the welds still represent a discontinuity in the track structure due to variations in microstructure, mechanical properties and residual stress levels with respect to the parent rail. These variations can play significant roles in increasing the risk of weld failure under service conditions. In order to better understand how FBW parameters affect these variations, the two main parameters; number of preheating cycles and upsetting forces were varied in three 56E1 rail welds, welded by a stationary FBW machine. Besides, these variations were systematically compared with those that occur in a standard thermite 60E2 rail weld. The thermite weld showed a heat affected zone (HAZ) extent much greater than those measured in the flash butt welds. The flash butt rail weld with a greater upsetting force (Standard Crushed) showed a HAZ extent larger than those in the other two welds (Standard Uncrushed and Narrow-HAZ Crushed), while the weld with fewer preheating cycles (Narrow-HAZ Crushed) showed a smaller extent of the HAZ.All welds showed pearlite colonies with proeutectoid ferrite at the prior austenite grain boundaries in the weld centre, and in the thermite weld zone. The rest zones across the welds exhibited almost fully pearlitic microstructures, but the pearlite at nearly the visible HAZ extents was partially spheroidised. The partially spheroidization zone had the minimum hardness across each of the thermite and flash butt welds. The Narrow-HAZ Crushed weld showed hardness in the weld centre, on average, higher than that of the parent metal. Moreover, the averaged hardness levels in this weld were significantly higher than those in the other two welds. However, these levels in the Standard Crushed weld were slightly lower than those in the Standard Uncrushed weld. Although the visible HAZ extent coincided with the point of minimum hardness, the residual stresses arising from the welds seem to extend much further. Contour Method and laboratory X-ray diffraction techniques were used together to measure the residual stress components across the thermite and flash butt rail welds. The longitudinal residual stress distribution showed tension in the web region along with compression in the head and foot regions of the rail welds. The vertical stress distribution across the flash butt welds was generally similar, and the maximum tensile stress values were comparable to those in the longitudinal direction. While the maximum values of the longitudinal tensile stress increased with decreasing the HAZ widths, these values in the vertical direction were significantly unaffected. However, the longitudinal and vertical tensile residual stresses typically promote the vertical straight-break and horizontal split web failure modes respectively.

Rail steels rely primarily on possessing adequate wear and rolling contact fatigue resistance. These properties, together with the toughness, can in principle be optimized by implementing thermomechanical processing assisted by controlled niobium additions. The purpose of the current work is to develop a Nb-microalloying strategy in the context of high-carbon pearlitic and cementite-free bainitic steels. The conventional methods do not leave the critical regions of a rail section in a suitably processed state. An attempt has been made for the first time, to create a pancaked austenite grain structure, with an examination of the consequences on the final product. One of the major difficulties is to ensure that niobium does not segregate during manufacturing, since niobium is a strong carbide former and rail steels traditionally contain large carbon concentrations. Niobium solubility in austenite has been assessed critically and thermodynamic calculations for microsegregation have been taken into account. The aim is to ensure that any primary niobium carbide precipitated from solute-enriched liquid during non-equilibrium solidification, can be taken into solution in austenite during reheating, to mitigate potential effects of coarse precipitates on the final mechanical properties. Rail steels containing 0.01-0.02 wt% Nb have been designed and characterised. In as-cast condition, primary niobium carbides as large as ~10 µm can be observed, which dissolve slowly during reheating. An attempt has been made to develop a model to estimate the dissolution kinetics of the carbides. Dissolved niobium in reheated austenite precipitates during hot deformation as fine niobium carbides (< 50 nm) which inhibit austenite recrystallisation by pinning the austenite grain boundaries. Nb-microalloying increases the ‘no-recrystallisation temperature’ of deformed austenite during multi-pass compression tests. The topology of grain deformation has been analysed in terms of stereological calculations and dilatometric experiments have shown that transformation kinetics tend to accelerate when the austenite is deformed below the no-recrystallisation temperature, however the effect is relatively small. The microstructure and mechanical properties of the as-rolled Nb-microalloyed steels have been characterised along with their rolling-sliding wear performance and compared with their non-microalloyed counterparts. Increased austenite grain boundary area and increased dislocation activity due to pancaking, hinder bainite growth which leads to an increased retained austenite volume fraction. This in turn, leads to slightly improved ductility, improved toughness and improved wear resistance in Nb-microalloyed bainitic alloys. Microstructural refinement in Nbmicroalloyed pearlitic alloys does not have any significant effect on tensile and toughness properties, but wear resistance improves significantly. A Bayesian neural network model has been developed to estimate the wear of rails. Predicted trends have been found consistent with metallurgical experience and the perceived noise levels are consistent with reasonable repeatability of the wear testing method used. The model can be applied widely to estimate wear because of its capacity to indicate uncertainty, including both the perceived level of noise in the output, and an uncertainty associated with fitting the function in the local region of input space.

In the introduction to a recent symposium on rolling contact fatigue, R.A.Smith stated that it was difficult to apply our greatly increased understanding of metal fatigue, to rolling contact fatigue, because of "the apparent lack of alternating tensile stresses to drive the cracks." He went on to say "alternating shear stresses are easily found, but the reproduction of continuous crack growth controlled by shear (Mode II in fracture mechanics terms), has proved to be near impossible." This project has demonstrated that under specific conditions this mode of growth does occur. The project began by studying rolling contact fatigue defects, in particular the 'squat' defect in railway lines, and the stress analyses that have been performed on them. It was concluded that the largest stress cycle experienced by the cracks must be a shear stress. It. series of tests were then performed that loaded a crack in pure shear, or a mixture of tension and shear, looking at the effects of using fully reversed shear loading, and the effects of applying tensile mean stresses to reduce the friction on the crack flanks. However these tests all produced less than one millimetre of mode II growth, before the cracks arrested or branched. The final series of tests however applied a tensile load cycle before each shear load cycle. This time coplanar growth was produced, that is the crack grew in the direction of the maximum shear stress. This type of load cycle is a simplification of the load cycle calculated by Bower and Johnson of Cambridge University, where the tensile load is produced by fluid trapped in the crack. Two crack growth rate formulae were produced that fitted the data, indicating that the growth rate was dependent on both the tensile and the shear parts of the cycle.

Modern railway transportation has imposed severe work conditions on the track. Wear of rails has become an important and costly phenomenon. Recent developments in the manufacture of rail steels have refined the interlamellar spacing to produce harder and more wear resistant pearlitic steels. Despite better nominal properties shown by bainitic and martensitic steels, pearlitic steels have shown lower wear rates. The aim of this study is to explain the mechanisms for the wear performance by observing how the lamellar pearlitic microstructure adapts to the wear loading. Four pearlitic rail steels, with similar chemical composition but with different hardnesses and interlamellar spacings, have been examined. Wear tests have been performed under both pure sliding and rolling-sliding conditions, the latter designed to simulate track conditions. The worn surfaces and the plastically deformed subsurface regions have been examined by optical metallography and scanning electron microscopy. It was observed that the plastic deformation produced considerable fracturing and realignment of the hard cementite lamellae. The effect of these realignments on the surface was to present an increased area fraction of hard cementite lamellae to the surface. Thinner cementite lamellae, associated with low interlamellar spacings, were easier to blend before fracturing. A relationship between the bulk hardness (HV) and the reciprocal root of the mean true interlamellar spacing has been proposed for fully pearlitic steels. Wear rates were found to be a function of the original bulk hardness, rather than the increased hardness of the plastically deformed layers. Also, wear rates were reduced as hardness increased by reducing the interlamellar spacing. Pure sliding and rolling-sliding wear tests ranked the four steels correctly. Furthermore, qualitative comparisons between experimental wear rates and those obtained in-track trials show the same scale in reduction of wear with increased hardness.

In order to find a feasible solution for a joining method of a sandwich side-wall, a sandwichfloor and a steel underbody of a railway vehicle, conceptual joint designs have been devel- oped by using structural optimization software.  It is shown that the joints are capable of carrying the loads assumed to act on the structure but that  several improvements to theanalysis needs to be done to assure a safe design.

This diploma thesis was prepared as an architectural study. The subject of the proposal was design of VRT station in Brno-Tuřany, near Brno airport. It was designed station building with platforms and four tracks. Two of them are passable and the other two are stationary. Rails leads below ground level. Above the rails is rail station that connect both areas next the rail corridor. Railway station serves primarily to transfer between rail and air transport.

Robotization of industry is very important in these days. It is possible to replace human workers with robots and because of that make manufacturing faster. This master’s thesis includes feasibility study of robotic welding for stainless steel part guide rail. Quality of robotic welding was evaluated on testing pieces. Robotic welding was 88,5 % faster than current welding method. Costs of manufacture of one piece were 40 % cut.

The work presented in this thesis is aimed at investigating the interaction between wear and rolling contact fatigue, which are two of the most serious forms of deterioration caused by the wheel on rail contact stresses. Wheel-rail contact conditions were simulated by a two disc contact using the LEROS (LEicester university ROlling-Sliding wear testing machine). Investigation of the wear behaviour of BS11 pearlitic rail steel showed that steady state wear behaviour is established after a certain number of rolling-sliding cycles. Contact surface failure by ratchetting (accumulation of unidirectional plastic strain) was found to be the dominant failure mechanism during the period leading to the steady state. This mechanism was confirmed by the drop in the wear rates when the direction of rolling-sliding; i.e. strain in the surface layer, was reversed at predetermined numbers of cycles. The effect of repeated rolling direction reversals on crack morphology, propagation and rolling contact fatigue (RCF) life of BS11 rail steel was also investigated. It was established that rolling direction reversal has a beneficial effect on RCF life. A new mechanism, the "variable crack face friction mechanism", was proposed to explain this effect. Interaction between wear and RCF fatigue was investigated through rolling-sliding experiments where specimens were run dry for certain number of cycles, to induce different levels of wear damage, before the fatigue performance was investigated. It was shown that initial dry cycles above a critical number causes sudden and significant deterioration in RCF life. This deterioration has been explained in terms of the role of the accumulation unidirectional plastic strain (ratchetting) in initiating and propagating the early cracks during the dry phase. A strong correlation was found between the total ratchetting strain induced during the dry phase and the deterioration in RCF life. An empirical relationship to estimate this deterioration was concluded.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The rolling-sliding dry-wear behaviour of a series of bainitic steels and a standard pearlitic rail steel have been compared over a range of contact stress and creepage conditions applicable to the British Rail network. A rolling-sliding wear machine has been constructed - LEROS - which allows very high contact stresses to be combined with high creepages under well controlled conditions. Materials were tested on LEROS and on an Amsler machine. Limited vibration analyses were carried out on both machines and compared with the frequencies of disc surface periodic undulations. No direct linkage was determined. Despite better standard mechanical properties, the wear resistance of lower carbon bainitic steels was inferior to that of the pearlitic steel. A bainitic steel with the same carbon content as the pearlitic steel wore a little less, but at considerable expense to the pearlitic wheel steel counter-material in the wear couple. The wear resistance of bainitic steels depends upon the volume fraction of hard phase, such as carbide and martensite-austenite phase, for rolling-sliding as well as other types of dry wear loading. Pearlitic steel performs exceptionally well under certain rolling-sliding conditions, such as the majority seen in these tests, since the lamellar microstructure is modified so as to present a greater area fraction of carbide hard phase at the wear surface, a fraction in excess of bulk volume fraction. Recommendations are made for the dry wear applicability of the steels.

A escória de aciaria LD é um coproduto originado do refino do ferro gusa em aço e da metalurgia secundária, sendo gerado, em média, uma quantidade de aproximadamente 120 kg/t de aço produzido. Assim como as escórias de alto-forno, que são utilizadas como matéria-prima para a fabricação do cimento, as escórias de aciaria LD, após beneficiamento (chamadas de agregados siderúrgicos), possuem diversas aplicações, tais como: artigos de concreto, diques marítimos, tratamentos de efluentes, lastro ferroviário, base e sub-base para pavimentos de rodovia, corretivo de solos, entre outros. Entretanto, este material possui compostos (CaO e MgO quando livres, Fe0, FeO e mCaO.nSiO2) que sofrem reações quando exposto ao ambiente, provocando expansão e desintegração dos materiais onde é aplicado, sendo necessária a estocagem em pátios para cura ou envelhecimento e consequente minimização da expansão. Atingido um determinado tempo de envelhecimento, o agregado é avaliado sob o ponto de vista do potencial de expansão para que, a partir dos resultados obtidos, seja ainda mantido sob cura ou destinado à sua aplicação. Os métodos mais comuns que avaliam a expansão de escórias de aciaria são o PTM-130/78, JIS A 5015/92 e o ASTM D4792/00. No Brasil, atualmente, o ensaio PTM-130 é o mais utilizado pelo Departamento de Estradas de Rodagem, entretanto o método leva 14 dias para obtenção dos resultados, que em geral são pouco detalhados sobre o comportamento da escória. Desta forma, o presente trabalho buscou correlacionar o método de avaliação do potencial de expansão volumétrica da escória de aciaria LD com a concentração de determinados compostos, quantificados através da difratometria de raios X em pós e o método de Rietveld, respectivamente. Buscou-se, também, compreender a influência dos diferentes compostos sobre a expansibilidade.
BOF slag is a byproduct originated from the hot metal refining to steel and its subsequent types of secondary metallurgy processes, being generated, on average, an amount about 120 kg/t of steel. Similar to blast furnace slag which is used as raw material for the manufacturing of cement, BOF slag, after treatment (so-called of steel slag aggregates), has many applications such as: concrete components, marine docks, effluent treatment, ballast, road and highways base, correction of soil, among others. However, BOF slag is composed by chemical products (such as free CaO and MgO, Fe0, FeO and mCaO.nSiO2) which suffer expansive reactions when exposed to the atmosphere, causing expansion and disintegration of the materials where it is applied. Therefore, it is required some temporary storage for curing or aging to minimize the volumetric instability that is evaluated trough the potential of expansion. Depending on the volumetric expansion results, steel slag aggregates may be approved or disapproved according to a specified limit that will allow to be used or not. The most common methods to evaluate the expansion of BOF slags are the PTM-130/78, JIS A 5015/92 and ASTM D4792:2013. In Brazil, PTM-130 test is currently the most used by the department of highways. This method spends 14 days to obtain the result that generally shows few details about the behavior. Thus, the present study has the purpose of correlating the traditional method of evaluation with the one of X-ray diffraction in powders associated to the Rietveld Method. Another goal is to understand the influence of different compounds on expansion.

Orientador: Maria Clara Filippini Ierardi
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A melhoria nas propriedades superficiais dos materiais tem sido buscada incessantemente pelas indústrias de transformação. A utilização do laser para tratamento térmico e refusão, entre outros processos, tem possibilitado grandes avanços nesta área. Muito se tem trabalhado na determinação dos parâmetros operacionais do laser e a resultante destas influências sobre as propriedades dos materiais. Os objetivos deste trabalho são estudar os efeitos destes parâmetros operacionais sobre a profundidade da camada superficial e a caracterização microestrutural das amostras submetidas a tratamento térmico a laser. Foram feitos experimentos usando os aços AISI 1045 e AISI 4340, a partir de amostras recozidas, temperadas e nitretadas. Foi utilizado um laser de CO2, pertencente ao LNLS, com potência nominal de 1 kW, desfocado em 2 mm, velocidade de deslocamento do feixe variando de 3000 a 10000 mm/min. Os resultados confirmam o laser como um instrumento eficaz na aplicação dos tratamentos superficiais. Para o aço AISI 1045, verifica-se que as amostras nitretadas apresentam maior profundidade da poça resultante após tratamento a laser. Já para o aço AISI 4340 as amostras endurecidas são as que se apresentam com maiores profundidades de poça. Para ambos os casos, as amostras recozidas apresentam os menores valores de profundidade da poça. Os ensaios de corrosão demonstram, com exceção das amostras nitretadas, uma tendência de elevação na nobreza do potencial eletroquímico do material. Quanto à resistência ao desgaste, com exceção das amostras nitretadas, do aço AISI 4340, todas as amostras apresentaram melhora após submetidas aos tratamentos propostos
Abstract: The industry development during last decades has allowed significant improvements concerning materials surface properties. Laser application for thermal treatment and remelting has also permitted important advances in this area. A lot of work has been spent in order to understand the influence of the operational laser parameters on the products¿ performance. The main objective of this study is to examine the effects of such parameters on the surface layer depth and on the typical microstructural arrangement of the treated samples. Thus, experiments were carried out using the steels AISI 1045 and AISI 4340, which were annealed, tempered and nitrated. Further, It was used a CO2¿s laser equipment, with nominal power of 1kW (defocusing of 2mm) and scan speed varying from 3000 mm/min to 10000 mm/min. The results confirmed the laser as an effective technique for surface treatments application. For steel AISI 1045, it was verified that nitrated samples presented the deepest liquid pool as consequence of the laser treatment. However, for steel AISI 4340, the hardened samples presented the deepest liquid pool. In both cases the annealed samples presented the lowest values concerning such parameter. The corrosion tests demonstrated that, except for the nitrated samples, a tendency of electrochemical potential increasing could be observed for all other studied conditions. Concerning wear resistance, excepting steel AISI 4340 nitrated samples, the others shown an improvement after the proposed treatment
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica

Orientadores: Paulo Roberto Mei, Antonio Jose Ramirez
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Neste trabalho foram estudadas as modificações metalúrgicas provocadas por tratamentos térmicos e soldagem por atrito com pino não consumível SAPNC do aço inoxidável supermartensítico AISM 12Cr/6Ni/2Mo/0,1Ti. As chapas de AISM foram fornecidas após laminação a quente e recozimento, com propriedades mecânicas e microestrutura fora do estabelecido pelos requisitos técnicos de controle de qualidade de materiais usados na indústria de transporte de petróleo e gás. Foi utilizada uma metodologia experimental que se consistiu em duas frentes de estudo: 1) Uso de tratamentos térmicos para reproduzir as condições microestruturais empregadas industrialmente; 2) Desenvolvimento de parâmetros de processamento superficial e soldagem de juntas por atrito. Para reproduzir as condições microestruturais das chapas usadas em campo foram realizados diferentes revenimentos intercríticos, em patamares de 610, 625, 650, 670, 700 e 720 °C durante 2,5 horas. Para estudar a cinética de transformação de fases foi usado um simulador termomecânico Gleeble 3S50¿ acoplado a uma fonte de radiação síncrotron, na instalação XTMS pertencente ao Laboratório Nacional de Luz Síncrotron (LNLS). Para o desenvolvimento de parâmetros de processamento e soldagem por atrito foi utilizado um equipamento dedicado para SAPNC no Laboratório Nacional de Nanotecnologia. Os estudos foram feitos empregando uma ferramenta de compósito de nitreto de boro cúbico policristalino com matriz metálica da liga de tungstênio-rênio (25% Re) na forma de pino cônico com rosca, medindo entre 9,2 e 9,5 mm de comprimento e ombro convexo de 25 mm de diâmetro. Foram avaliadas velocidades de rotação na faixa entre 200 e 400 RPM, e velocidades de avanço entre 75 e 100 mm.min-1. Foram reproduzidas as condições de dureza e fração de fases de uma tubulação comercial de AISM, mediante revenimentos intercríticos. A melhor temperatura de revenimento intercrítico foi 610°C, pois conseguiu gerar uma matriz de martensita revenida, com presença de 15% de Foi possível obter um processamento com bom acabamento e livre de defeitos internos, usando 250 RPM e 100 mm.min-1. Para a soldagem de dois passes de juntas de chapas de 17,9 mm de espessura, a melhor combinação de parâmetros foi 300 RPM e 100 mm.min-1. Para os dois estados de fornecimento (recozido; temperado e revenido), a zona misturada consistiu de blocos martensita nova com refinamento progressivo de grão em direção à raiz dos cordões. Foram identificadas 3 zonas termicamente afetadas (ZTA) em relação às 5 que ocorrem na soldagem a arco. Não foram encontradas as ZTAs i e ii (de alta temperatura), suprimindo completamente a precipitação de ferrita delta. A ZTA iii (de austenitização completa) era totalmente constituída de martensita nova. A ZTA iv (de austenitização intercrítica) de chapas recozidas era formada por uma mistura de martensita nova e martensita revenida. A ZTA iv de chapas temperadas e revenidas apresentou uma mistura de martensita nova, martensita revenida e austenita revertida
Abstract: In this research, metallurgical changes due to heat treatments and friction stir welding of a high alloyed supermartensitic stainless steel SMSS 12Cr/6Ni/2Mo/0, 1Ti were studied. SMSS plates were received after hot rolling and annealing. Mechanical properties and microstructure were out of the technical requirements established for materials quality control used in the oil and gas transportation. An experimental methodology was used to evaluate two different areas: 1) The use of heat treatments to replicate the microstructural conditions used in field applications. 2) Development of friction stir processing and welding parameters. The microstructural conditioning was conducted by using different intercritical tempering temperatures: 610, 625, 650, 670, 700 and 720 °C during 9000 seconds. To study the kinetics of phase transformation during heating, soaking and cooling, it was used a thermomechanical simulator Gleeble3S50¿, coupled to a source of synchrotron radiation, at XTMS facility belonging to the Brazilian Synchrotron Light Laboratory. The development of friction stir processing and welding parameters was conducted in dedicated equipment for FSW at the National Laboratory for Nanotechnology. A composite W-Re (matrix)/PCBN reinforced tool with 9.2 to 9.5 mm long threaded conical pin and convex threaded shoulder was used. Spindle speeds between 400 RPM and 200 RPM, and welding speeds between 100 and 75 mm.min-1, were evaluated. It was possible to replicate the hardness and phase fractions of a commercial SMSS pipe by using an intercritical tempering. The best temperature was 610 °C, since it can generate a tempered martensite matrix with 15% of reverted austenite and 2% of fresh martensite after cooling at room temperature. It was also possible to obtain a sound defect-free processing using 250 rpm and 100 mm.min-1. To perform a two passes welding joint of 17.9 mm thickness, the best combination of parameters to obtain good surface quality and minimal amount of internal defects was 300 RPM and 100 mm.min-1. For the two microstructural conditions evaluated (hot rolled and annealed; and quenched and tempered), the nugget zone consisted of blocks of fresh martensite with progressive grain refinement toward the root of the welded passes. Three heat affected zones HAZ, were identified, regarding the five reported by arc welding. The HAZ i and ii (high temperature) were not found, completely suppressing the delta ferrite precipitation. The HAZ iii (fully austenitized) consisted of fresh martensite. The HAZ iv (partially austenitized) of hot-rolled and annealed plates consisted of a mixture of fresh martensite and tempered martensite. The HAZ iv of quenched and tempered plates consisted of a mixture of fresh martensite, tempered martensite and reverted austenite
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

Este trabalho apresenta um estudo sobre a formação e evolução da camada de nitretos sobre substrato de ferro com pureza de 99,83% e do aço AISI H12, nitretados por plasma. As camadas foram obtidas com a variação sistemática das condições de nitretação, como temperatura, tempo e frequência do plasma. A atmosfera de trabalho empregada foi a de uma mistura gasosa de 20% N2 + 80% H2, mantida à pressão constante de 6 mbar, sob fluxo. Uma investigação detalhada da camada nitretada das amostras de ferro foi feita através de desgaste mecânico em passos sucessivos e após cada desgaste, as novas camadas foram analisadas por espectroscopia Môssbauer de elétrons de conversão (CEMS) auxiliadas por outras técnicas, como difração de raios X, microdureza e microscopia ótica e eletrônica. As análises superficiais demonstraram que a camada nitretada é formada por uma mistura de nitretos γ-Fe4N, ε-Fe3N e-ε-Fe3,2N, que variam suas proporções com as condições de nitretação. Abaixo desta camada outros nitretos são formados como e ε-FeXN (2≤X≤3,2) e α-Fe16N2. No aço H12, foi estudada a influência da nitretação por plasma em correntes contínua e pulsada. As amostras foram caracterizadas quanto ao perfil de microdureza, perfil de concentração de nitrogênio, difração de raios X e espectroscopia Môssbauer de elétrons de conversão (CEMS) e de raios X de conversão (CXMS). A camada composta próxima à superfície, como vista por CEMS, consiste de uma mistura de γ-Fe4N e ε-FeX(N, C) enquanto a camada próxima à zona de difusão, investigada por CXMS, consiste de uma mistura de fases γ-Fe4N, ε-FeX(N, C) Fex(N, C), α-Fe16N2 e γ-austenita. O crescimento da camada nitretada quando difundida utilizando corrente contínua segue uma lei parabólica, o que não ocorre com o processo com corrente alternada. Este efeito deve ser devido à taxa de \"sputerring\" do catodo e da difusão auxiliada por radiação, que são mais acentuadas no caso de corrente alternada, para tempos de nitretação t ‹ 2h. A situação é revertida para t › 3h.
This work investigates the formation and evolution of nitride layers on a 99.83% pure iron and a AISI H-12 steel substrates by using plasma nitriding processoThe layers were obtained by systematic variation of the nitriding conditions, such as temperature, time and plasma frequency. The employed atmosphere consisted of a gaseous mixture of H2-20% N2, at a constant pressure of 6.0 mbar in f1ux.A detailed investigation of the nitrided layer on iron samples was performed through surface mechanical wear in successive steps. After each step the layer was analysed by Conversion Electron Mõssbauer spectroscopy (CEMS), as well as by other techniques, as X-ray diffraction, microhardness and optical and electronic metallography. The surface analysis of iron samples showed that the nitrided layers are formed bya mixture of γ-Fe4N, ε-Fe3N e-ε-Fe3,2N nitrides, whose proportions have varied with the nitriding conditions. Below this layer, different nitrides are formed, ε-FeXN (2≤X≤3,2) e α-Fe16N2. For H-12 steel substrates it was also studied the influence of direct and pulsed current on the layer. The samples were characterized related to the microhardness profile, nitrogen concentration profile, Xray diffraction and Conversion Electron and X-ray Mõssbauer spectroscopy (CEMS) and (CXMS). The near-surface compound layer, as probed by CEMS, consisted of a mixture of γ-Fe4N e ε-FeX(N, C) phases. The near-diffusion zone compound layer, as probed by CXMS presented a mixture of γ-Fe4N , e ε-FeX(N, C) Fex(N, C), α-Fe16N2e γ and- e γ-austenite phases. For the plasma process, the growth of the nitride layers in direct current follows the parabolic law, what does not occur when process with pulsed current is used. This effect is probably due to cathode rate sputtering and radiation-enhanced diffusion, the latter being more accentuated in the case of pulsed current, for nitriding times t ‹ 2h. The situation is reversed for t › 3h.

Orientador: Célia Marina de Alvarenga Freire
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: O hidrogênio é reconhecido como sendo um elemento residual sempre prejudicial ao aço. Proveniente de reações químicas e eletroquímicas, tais como, corrosão, proteção catódica e reações de processo, é absorvido pelo aço e retido nos defeitos da rede cristalina podendo causar a fragilização do aço e a propagação de trincas e fraturas. O presente trabalho visa analisar a influência do hidrogênio na estrutura cristalina e no comportamento magnético do aço AISI 4340 obtido pelas normas AMS 6414K e 6415S, nas condições como recebido, temperado e revenido. Para tanto corpos-de-prova foram retirados da posição transversal dos lingotes, temperados a 845°C e revenidos a três diferentes temperaturas (350°C, 400°C e 500°C). Para a caracterização do material foram feitas micrografias, ensaios de dureza, difração de raios-X, voltametria cíclica e análise de difusão. As propriedades magnéticas foram obtidas utilizando-se um magnetômetro de amostra vibrante (VSM) onde a magnetização de saturação foi obtida e foram analisadas amostras antes da hidrogenação e após hidrogenação. O carregamento de hidrogênio foi feito em solução de H2SO4 a 0,05 M em temperatura ambiente. Os resultados obtidos nos ensaios de voltametria cíclica e difusão foram correlacionados às difrações de raios-x e magnetização de saturação em função da contaminação por hidrogênio e as diferentes condições de tratamento térmico. A comparação das curvas antes e após hidrogenação para as difrações de raios-X mostraram que a hidrogenação provoca uma diminuição das curvas em todas as condições de tratamento térmico para os dois tipos de aço. As curvas de difusão mostraram que os coeficientes de difusão da amostra como recebida é menor que as tratadas com revenimento para o aço AISI 4340 AMS 6415S e maior para o aço AISI6414K. A magnetização de saturação mostrou que os aços AISI 6414K e 6415S antes da hidrogenação apresentaram magnetização de saturação maior que após hidrogenação
Abstract: Hydrogen is recognized as a residual element always harmful to steel. From chemical and electrochemical reactions, such as corrosion, cathodic protection and reaction process, the steel is absorbed and retained in the crystal lattice defects may cause embrittlement of steel and propagation of cracks and fractures. This study aims to analyze the influence of hydrogen in the crystal structure and magnetic behavior of AISI 4340 obtained by the rules AMS 6414K 6415S and the conditions as received, quenched and tempered. For this purpose the test piece bodies were removed from the transverse position of the ingots, quenched to 845 ° C and tempered at three different temperatures (350 ° C, 400 ° C and 500 ° C). For the characterization of the micrographs were taken, hardness tests, X-ray diffraction, cyclic voltammetry analysis and dissemination. The magnetic properties were obtained using a vibrating sample magnetometer (VSM), where the saturation magnetization was obtained and analyzed samples before hydrogenation and after hydrogenation. The hydrogen loading was done in a solution of 0.05M H2SO4 at room temperature. The results obtained in the test and cyclic voltammetry were correlated to diffusion x-ray diffraction and saturation magnetization due to hydrogen contamination and different heat treatment conditions. A comparison of the curves before and after hydrogenation for X-ray diffraction showed that the hydrogenation causes a decrease of the curves in all heat treatment conditions for both types of steel. The curves show that the diffusion coefficient of diffusion of the sample as received is lower than those treated with tempering for the steel AISI 6415S AMS 4340 steel and higher for AISI6414K. The saturation magnetization showed that AISI 6415S 6414K and exhibited before the hydrogenation higher than saturation magnetization after hydrogenation
Doutorado
Materiais e Processos de Fabricação
Doutora em Engenharia Mecânica

Os efeitos da textura e do tamanho de grão de bobina a quente (BQ) na evolução da textura durante o processamento de aços elétricos semiprocessados foram estudados no presente trabalho. Observou-se que o aumento do tamanho de grão da BQ não é eficiente para obtenção de altas intensidades de componente Goss () após recozimento intermediário quando a bobina a quente apresenta intensidades muito elevadas (em torno de 14 vezes o aleatório) de cubo rodado (). Foi confirmada a hipótese de que ocorre nucleação de grãos com orientação Goss e cubo na face () em bandas de transição de grãos de fibra gama (//DN). Além disso, os resultados sugerem que a textura da BQ é importante para a evolução da textura durante o processo, levando à texturas finais distintas. Observou-se também forte relação entre tamanho de grão inicial (da BQ) e após laminação a frio e recozimento intermediário. Quanto maior o tamanho de grão inicial, maior o tamanho de grão recristalizado. O mesmo comportamento ocorreu durante o recozimento final, etapa em que ocorre migração de contornos induzida por deformação. Quanto maior o tamanho de grão após recozimento intermediário, maior o tamanho de grão após laminação de encruamento e recozimento final. Resultados interessantes foram obtidos a partir de chapas produzidas por solidificação direcional, encontrando-se texturas finais próximas a ideal, principalmente quando se utilizaram laminações a 800ºC.
The grain size and hot band texture effects on the texture evolution during the semi processed electrical steels were studied in this work. The results show that the increase of the hot band grain size is not efficient to obtain high Goss intensities () after intermediate annealing, when the hot band texture presents high intensities (around 14 times random) of rotate cube (). The nucleation of Goss and cube grains () in transition bands of gama fiber grains (<111//DN) was observed. Moreover, the results found in this work suggest that hot band texture is determinant to the texture evolution during the process. Strong influences of hot band grain size in recrystallized grain size after intermediate annealing was found. Samples produced by coarse grains presented high recrystallized grain sizes. The same comportment after temper rolling and final annealing was found, when strain induced boundary migration occurs. Coarse grains after intermediate recrystallization let to high grain sizes after final annealing. Excellent textures for samples produced from directional casting were found, mainly when the sheets were rolled at 800ºC.

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Atualmente, as cargas aplicadas nos eixos de vagões ferroviários têm sofrido aumento de esforços devido ao choque e tração no engate ferroviário. Neste trabalho o estudo foi realizado no engate tipo “F”, que tem maior utilização e interesse por parte da ferrovia, por se tratar de um engate rotativo e utilizado para descarregamento de vagões com os mais diversos tipos de carga. Este trabalho tem como objetivo, verificar se existem transformações da microestrutura no material do engate, e possíveis gerações de trincas, através do estudo do aço AAR M-201 Grau E, após o ensaio de partículas magnéticas, com corrente alternada através da aplicação de Prods. A faixa de amperagem variou-se de 100 a 1000 ampères e como meio de resfriamento, utilizou-se a água a temperatura ambiente e o ar forçado. A preparação foi feita partindo de um engate Tipo “F” completo, fornecido por um operador logístico, a cauda foi magnetizada por inteiro e depois separados os corpos de prova por corte de serra, refrigerado para não haver aquecimento. Para a caracterização microestrutural, utilizou-se uma preparação metalográfica de laboratório de bancada e ataque com Nital 2%, e fez-se uso de microscopia ótica convencional e microscopia eletrônica de varredura (MEV). Através da utilização da microscopia ótica e da microscopia eletrônica de varredura (MEV), pode-se verificar a microestrutura nas áreas que sofreram alterações microestruturais. Concluiu-se que o aço do engate, AAR M-201 grau E, após a magnetização por Prods de 300 a 1000 ampères, apresentou alteração microestrutural, onde observou-se uma estrutura de martensita acicular não revenida e geração de trincas, a mesma alteração microstrutural foi observada em amostras com resfriamento ao ar, porém sem a geração de trincas, em ampliações de 50 vezes foi nítido o efeito de queima provocado pelo Prods no material, bem como sua extensão, evidenciando áreas centrais de atuação do Prods, zonas de transição e áreas não afetadas. As trincas tiveram comportamento de propagação intergranular, para ampliações de 9300 vezes em MEV, pode-se observar que as mesmas se propagaram somente nas áreas com martensita e contornaram as áreas com maior presença da fase ferrítica.
Currently, the applied loads on the axles of railway cars has been increasing efforts due to shock and traction in railway coupling. In this work, the study was performed on the coupling type "F", which has increased use and interest on the part of the railway, because it is a rotary coupling and used for unloading of wagons with the most diverse types of cargo. This work aims, check for microstructural changes on the coupling material, and possible generation of cracks through the study of steel AAR M-201 grade and after the test of magnetic particles with alternating current by applying Prods. As amperage range, was varied from 100 to 1000 amps and as cooling medium water was used at room temperature and forced air. The preparation was made starting from a coupling type "F" full, provided by a logistics operator, the tail was magnetized in full and then separate the specimens by cutting saw, cooled to no heating. For microstructural characterization, we used a metallographic preparation of benchtop laboratory and attack Nital 2%, and was made use of conventional optical microscopy and scanning electron microscopy (SEM). By using light microscopy and scanning electron microscopy (SEM), you can check the microstructure in areas that suffered microstructural changes. It was concluded that the coupling of steel, AAR M-201 grade And after magnetization by Prods 300-1000 amps, presented change microstructural where there was a martensite acicular structure not tempered and generation of cracks, the same change microstructural was observed in air to cooling with samples, but without generating cracks at magnifications of 50 times was clear the burning effect caused by Prods in the material as well as its extension, showing the central areas of the Prods activities, transition zones and unaffected areas. The intergranular crack propagation behavior had to 9300 times magnification under SEM, it can be seen that they have spread only in areas with martensite and rounded areas with the greatest presence of the ferritic phase.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

O desenvolvimento de componentes com geometrias complexas e funcionalidade superficial representa um grande desafio científico atual. O processo Metal Injection Molding (MIM) tem representado, nos últimos anos, uma grande alternativa para a produção de aços com estas características e elevada produtividade. Existe uma crescente demanda referente ao estudo e utilização de aços inoxidáveis MIM e a melhora de suas propriedades mecânicas e metalúrgicas superficiais. Com a aplicação de engenharia de superfície é possível obter aumento da microdureza superficial, da resistência ao desgaste, da vida em fadiga e da resistência à corrosão. Uma das características emblemáticas dos aços MIM é seu maior volume de porosidade, quando comparado aos aços obtidos pelos processos convencionais. Destaca-se que o volume de porosidade pode ter efeito negativo em relação à resistência mecânica e à corrosão nestes aços. O volume de porosidade também colabora para que componentes produzidos por este processo sejam fortemente influenciados, por efeitos de erosão de bordas, e dificuldade de difusão uniforme, em regiões com furação, inibindo a homogeneização das camadas de compostos e difusão. Neste trabalho objetivou-se desenvolver as ligas em aços inoxidáveis a partir de pós metálicos aglutinados com polímeros e pesquisar as propriedades metalúrgicas e mecânicas superficiais, obtidas a partir da aplicação de tratamento termoquímico de Oxinitrocarbonetação (QPQ), nos aços inoxidáveis MIM AISI 316L e 17-4 PH e o efeito do acabamento intermediário jateado na resistência a corrosão, que representa modificação deste processo. Os ciclos de difusão utilizados foram referendados a partir de tempos de 30, 60 e 120 minutos utilizando-se temperatura de nitrocarbonetação 570ºC e de oxidação 380ºC. As avaliações das propriedades das amostras oxinitrocarbonetadas foram realizadas em ensaios de microscopia óptica, microscopia eletrônica de varredura, microdureza Vickers, polarização potenciodinâmica anódica, difração de raios - X (para determinação das fases na camada de compostos) e difração de raios - X (para determinação de tensões residuais). Os resultados obtidos demonstraram efetivo aumento da microdureza superficial, formação de camada de compostos monofásica, melhora da resistência a corrosão e tensões residuais compressivas na superfície dos aços AISI 316 L e 17 4 PH MIM.
The development of components with complex geometries and surface functionality is a current scientific challenge. There is an increasing demand related to the study and use of stainless steel Metal Injection Molding (MIM) and the improvement of their surface mechanical and metallurgical properties. With the application surface engineering it is possible to obtain increased surface hardness, wear resistance, fatigue life and corrosion resistance. One of the iconic features of MIM steels is its largest volume of porosity, when compared to conventional steels. It is noteworthy that the volume of porosity may have a negative effect on the mechanical and corrosion resistance. The volume porosity also contributes to components produced by this process are strongly influenced by edge effects of erosion and uniform diffusion regions difficulty with drilling, inhibiting the mixing of compounds and diffusion layers. Other research has shown that high volumes of porosity may be associated with the presence of corrosive pitting progressively accentuate the deterioration of these materials. In this work we were researched surface metallurgical and mechanical properties of the thermochemical treatment application Oxinitrocarburizing- QPQ in stainless steel AISI 316L ME and 17 4 PH and the effect of the intermediate blasted finish on the corrosion resistance. Assessments of properties of the samples Oxinitrocarburizing by QPQ process were carried out in optical microscopy tests, scanning electron microscopy, Vickers hardness, anodic potentiodynamic polarization, diffraction X - ray (determination of the phases in the compound layer), and - ray diffraction x (residual stresses).The results demonstrated effective increase of the surface hardness, forming a single phase compound layer improves the corrosion resistance and compressive residual stresses on the surface of steels AISI 316 L and 17 4 PH MIM.

Este trabalho apresenta a análise de provas de carga dinâmica realizadas em estaca metálicas tipo trilho (TR - 68) cravadas no Campo Experimental de Fundações da USP/São Carlos. As estacas possuem segmentos de 12 e de 3 m, soldados segundo a NBR 8800/86, totalizando um comprimento máximo 27 m. Os objetivos desta análise são: 1) realizar um estudo abrangente da capacidade de carga do tipo trilho, 2) verificar a utilização de trilho usado como elemento estrutural de fundação, 3) comprovar o uso do repique como método de controle do estaqueamento, 4) demostrar a importância da energia crescente na prova de carga dinâmica. As medidas de repique foram realizadas com o uso de papel e lápis em vinte estacas, para níveis crescentes de energia. A energia foi aplicada pelo martelo de gravidade caindo de uma altura de 0,20 - 0,40 - 0,60 - 0,80 - 1,00 - 1,20 e 1,50 m. A capacidade de carga das estacas, determinada pela extrapolação da curva carga mobilizada - deslocamento, foi comparada com os valores obtidos pelos métodos de previsão da prática brasileira, bem como com os resultados de dois ensaios com PDA (Pile Driving Analyzer) e também com uma prova de carga estática, realizados em estacas representativas.
This paper presents an analysis of dynamic load tests performed on steel crane rails piles (TR-68) at the Experimental Foundation Field of USP/São Carlos. The piles have segments of 12 and 3 m, welded according to NBR 8800/86, comprising a maximum driving length of 27 m. The objectives of this analysis are: 1) to carry out a wide study of steel track pile bearing capacity, 2) verify the utilization of the steel crane rails piles with structural element of foundation, 3) to prove the use of the rebound with the control method of driving piles. 4) to demonstrate the importance of increasing energy in the dynamic load test. The rebound measurements were performed with paper and pencil in twenty piles and were analyzed by applying increasing energy level. The energy was applied by the gravity hammer falling of a drop heights of 0.2 - 0.4 - 0.6 - 0.8 - 1.0 - 1.2 and 1.5 m. The pile bearing capacity, determined by the extrapolations of the mobilized resistance - displacement curves was compared to the Brazilian experience methods, as well as to two load tests employing the Pile Driving Analyzer (PDA) and to one static load test carried out on representative piles.

As distorções de forma e variações dimensionais, em muitos casos, manifestam-se de maneira mais expressiva após a têmpera por indução ocasionando o chamado empenamento. Tais efeitos usualmente trazem despesas em reparos e restauração de peças, equipamentos e estruturas. Assim, a análise de tensões residuais é uma etapa obrigatória na produção de peças e elementos estruturais para a estimativa da sua confiabilidade sob condições reais de serviço. No presente trabalho foram realizadas medições de tensões residuais em semi-eixos automotivos fabricados com o aço DIN 38B3 temperados por indução. Estes eixos apresentaram diferenças quanto ao comportamento em distorção, com um eixo tendo sido endireitado e outro não. Devido a estas diferenças também se esperam diferenças em termos de distribuição de tensões residuais e propriedades dos eixos. As tensões residuais foram medidas através do método de difração de raios-X com dois equipamentos de medição (difratômetro portátil e difratômetro fixo). Complementando o trabalho foram feitas análises químicas, metalográficas, perfil de microdureza e profundidade de camada efetiva para verificar eventuais diferenças ou semelhanças entre os eixos analisados. Com os resultados de tensões obtidos foi possível obter uma visão geral da variação do perfil de tensões residuais superficiais após a têmpera por indução e a grande influência da etapa de endireitamento na redistribuição de tensões no material.
The distortions of form and dimensional variations, in many cases, appear after induction hardening causing the often called warping. These effects usually usually increase the costs of maintenance and restoration of parts, equipment and structures. Thus, the residual stress analysis is an important step in the production of parts and structural elements to estimate of its reliability under actual service conditions. In this study, measurements of residual stresses were carried out for a driveshafts manufactured from the DIN 38B3 steel after induction-hardening and straightening, if necessary. These shafts showed different behavior in distortion, with a shaft has been straightened and the other not. Due to these differences also are expected differences in the distribution of residual stresses and properties of the shafts.The residual stresses were measured by the X-ray diffraction method with two measuring equipment (a portable and a fixed diffractometers). Complementing this work chemical analysis, metallographic, of the microhardness profile and of effective case depth were accessed to eventually find differences or similarities between the analyzed driveshafts. With the residual stress results obtained it was possible to get an overview of the variation of the surface profile of residual stresses after induction hardening and the influence of straightening steps on the redistribution of residual stresses in the material.

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Proact Empreendimentos Tecnológicos S/C Ltda
This paper presents an evaluation of the effects of strain hardening on the kinetics of nitriding thermochemical treatment of alloys of ferritic steels AISI 430 and AISI 439 for different degrees of plastic deformation. The technique used to apply the plastic deformation level was increased by a universal tensile machine. Then we proceeded to apply the processes of gas nitriding, in salt baths and plasma, the alloys in the annealed condition and for different degrees of hardening. The samples were characterized by optical microscopy, scanning electron microscopy, hardness tests and examination of the microhardness profile of the layers. It also employed the technique of X-ray diffraction in order to determine the phases present in the nitrided layer. As a result of this study, it was found that the hardening has no effect on the kinetics of nitriding processes, nor levels of hardness achieved in the nitrided layer. The layer thickness was raised to a gas nitriding process, which besides the exposure time at temperature was held at temperature higher than the other processes studied. This study also presents the results of microstructure and curves of the percentage of nitrogen and carbon depending on the depth of the nitrided layer. Note that the nitrogen concentration decreases with depth as approaching the base metal. Carbon, in turn, is pushed into the sample, providing a decarburization in the region enriched in nitrogen and carbon accumulation in the regions just below the nitrided layer. The spectra of X-ray diffraction corresponding to the nitrided layers of steels 430 and 439 indicated the presence of CrN precipitate rich in nitrogen. The alloy 430 suffered heavy attack to a depth of about 30 Um on the other hand the alloy 439 had the region with little predominance of attack, with small volume fractions of more intense attack. The hardness levels of light and dark regions were similars, around 1000 HV, indicating an efficient mechanism of precipitation hardening. It concluded that the chromium nitride is present in both regions, and the highest attack can be related to a discontinuous precipitation process, probably due to iron nitride Fe3N, contrary to what was found in the literature.
O presente trabalho apresenta uma avaliação dos efeitos de encruamento na cinética do tratamento termoquímico de nitretação em ligas de aços inoxidáveis ferríticos AISI 430 e AISI 439 para diferentes graus de deformação plástica. A técnica empregada para se aplicar a deformação plástica em nível crescente foi por meio de uma máquina universal de tração. Em seguida procedeu-se a aplicação dos processos de nitretação gasosa, em banhos de sais e por plasma, nas ligas no estado recozido e para os diferentes graus de encruamento. As amostras foram caracterizadas por microscopia óptica, microscopia eletrônica de varredura, ensaios de dureza e levantamento do perfil de microdureza das camadas. Foi empregada também a técnica de difração de raios-X, com o objetivo de se determinar quais as fases presentes na camada nitretada. Como resultado principal deste estudo, concluiu-se que o encruamento não apresentou nenhum efeito na cinética dos processos de nitretação, nem tão pouco nos níveis de dureza atingidos nas camadas nitretadas. A espessura da camada foi maior para o processo de nitretação a gás, que além do tempo em exposição em temperatura, foi realizada em temperatura superior aos outros processos estudados. Este estudo também apresenta os resultados de microestrutura e as curvas de percentual de nitrôgenio e carbono em função da profundidade de camada nitretada. Nota-se que a concentração de nitrogênio diminui com a profundidade à medida que se aproxima do metal base. O carbono, por seu turno, é empurrado para dentro da amostra, promovendo uma descarbonetação na região enriquecida em nitrogênio, e um acúmulo de carbono nas regiões logo abaixo da camada nitretada. Os espectros de difração de raios-X correspondentes às camadas nitretadas dos aços 430 e 439, indicaram a presença do precipitado rico em nitrogênio CrN. A liga 430 sofreu ataque intenso até uma profundidade da ordem de 30 Um; já a liga 439 apresentava predominância de região com pouco ataque, com pequena fração volumétrica de ataque mais intenso. Os níveis de dureza da região clara e escura eram similares, por volta de 1000 HV, indicando um eficiente mecanismo de endurecimento por precipitação. Infere-se que o nitreto de cromo se faz presente nas duas regiões, sendo que o maior ataque pode estar relacionado a um processo de precipitação descontínua, provavelmente associado ao nitreto de ferro Fe3N, contrariamente ao que se encontrou na literatura.

O desenvolvimento e validação de métodos analíticos é um procedimento necessário quando um método não normalizado é utilizado por um laboratório de ensaios. A validação de métodos também é um requisito específico da norma ABNT NBR ISO/IEC 17025, que determina os requisitos gerais para a competência dos laboratórios de ensaio e calibração. O objetivo da validação é demonstrar que o método analítico, nas condições em que é executado, produz resultados com a exatidão requerida. O Laboratório de Corrosão, Proteção e Reciclagem de Materiais (LACOR), da UFRGS, tem o ensaio de determinação de metais por fluorescência de raios X, acreditado pelo CGCRE/INMETRO, conforme ABNT NBR ISO/IEC 17025. O ensaio é feito usando o método de espectrometria de fluorescência de raios X por dispersão de energia (EDXRF). Este método, contudo, não é normalizado e, portanto, o mesmo foi validado, neste trabalho de pesquisa, para atender a este requisito. A validação foi feita com base no documento orientativo DOQ-CGCRE-08 e no guia EURACHEM. Os parâmetros de validação, para o ensaio quantitativo por EDXRF, que foram calculados neste trabalho são: seletividade; limite de detecção (LD) e limite de quantificação (LQ); linearidade e faixa de trabalho; veracidade de medição (tendência, erro normalizado, Z-score e comparação com método de referência) e precisão (repetibilidade, precisão intermediária e reprodutibilidade). Além disso, foi desenvolvida uma metodologia de cálculo de incerteza de medição para o ensaio por EDXRF Os resultados obtidos neste estudo demonstram que o método EDXRF, usado na determinação de metais em aços, é um método não normalizado validado e compatível com os resultados obtidos com os métodos de referência: espectrometria de fluorescência de raios X por dispersão de comprimento de onda (WDXRF), fotométricos e espectrometria de absorção atômica (AAS). Inclusive, o WDXRF é um método de referência usado em muitas normas internacionais, que descrevem métodos de análise de aços por fluorescência de raios X, como ASTM E572 ou ASTM E1085. O estudo desenvolvido nesta dissertação permitiu que o LACOR mantivesse sua acreditação no ensaio de determinação de metais por fluorescência de raios X, na avaliação do CGCRE/INMETRO, no presente ano. Outros frutos deste trabalho foram a confecção das curvas de calibração do espectrômetro NITON XL3t GOLDD+ e a revisão do procedimento de ensaio, onde esses novos conhecimentos sobre a técnica EDXRF foram aplicados. Futuramente, este trabalho pode ser usado por outros pesquisadores para desenvolver estudos em outras matrizes metálicas, como cobre, alumínio, titânio ou níquel, e, também, em outras áreas de aplicação como jóias, reciclagem de materiais metálicos ou, até mesmo, para análise elementar de resíduos retidos em membranas de troca iônica.
The development and validation of analytical methods is a required procedure when a non-standard method is used by a testing laboratory. Method validation is also a specific requirement of the ABNT NBR ISO / IEC 17025, which determines the general requirements for the competence of testing and calibration laboratories. The purpose of validation is to demonstrate that the analytical method, under the conditions in which it is performed, produces results with the required accuracy. The Corrosion, Protection and Recycling Materials Laboratory (LACOR), at UFRGS, has the X-ray fluorescence metal analysis, accredited by CGCRE / INMETRO, according to ABNT NBR ISO / IEC 17025. The test is performed using Energy Dispersive X-Ray Fluorescence spectrometry, EDXRF method. This method, however, is not standardized; therefore, it was validated in this research to meet this requirement. The validation was based on the DOQ-CGCRE-08 document and the EURACHEM guide. The method performance calculated in this study for quantitative testing by EDXRF are: selectivity; limit of detection (LOD) and limit of quantification (LOQ); linearity and working range; trueness (bias, normalized error, Z-score and comparison with reference method) and precision (repeatability, intermediate precision and reproducibility). In addition, a measurement uncertainty calculation methodology was developed for the EDXRF testing The results obtained in this study demonstrate that the EDXRF method, used in the determination in the chemical analysis of steels, is a validated non-standard method and compatible with the results obtained with the reference methods: Wavelength Dispersive X-Ray Fluorescence spectrometry (WDXRF), photometric and atomic absorption spectrometry (AAS). In addition, WDXRF is a reference method used in many international standards, which describes analysis of steels by X-ray fluorescence spectrometry such ASTM E572 or ASTM E1085. The study developed in this dissertation allowed LACOR to maintain its accreditation in the test of metal by X-ray fluorescence analysis, in the CGCRE / INMETRO audit, this year. Other fruits of this work were the preparation of calibration curves of NITON XL3t GOLDD + spectrometer and complete revision of testing procedure, where this new knowledge about the EDXRF technique was applied. In the future, this work can be used by other researchers to develop studies in other base metals such as copper, aluminum, titanium or nickel, and also in other areas of application such as jewelry, recycling of metallic materials or even for analysis elemental residues retained in ion exchange membranes.

Este trabalho tem a intenção de contribuir com informações sobre a integridade superficial resultante do processo de torneamento em material endurecido de componentes mecânicos fabricados em aço cementado ABNT 8620 (DIN 21 NiCrMo 2). A análise das tensões residuais do corpo de prova foi experimentalmente conduzida pelo Método do Furo Cego Incremental, no qual um pequeno furo é introduzido na superfície do componente e a deformação aliviada é registrada por meio de extensômetros especiais, e também, pelo método da difração de raios-X. A superfície foi analisada através de parâmetros obtidos do mapeamento tridimensional da topografia superficial com instrumento de interferometria laser. Os parâmetros de rugosidade, selecionados para medição, visaram uma caracterização funcional das superfícies obtidas, tais como capacidade de carga, capacidade de retenção de fluidos lubrificantes e resistência ao desgaste. Também foram executados ensaios metalográficos para avaliar a existência de camadas de material alteradas abaixo da superfície. Os resultados indicaram que o torneamento em material endurecido foi capaz de produzir uma superfície resultante com boa área de contato, boa capacidade de carregamento e razoável capacidade de retenção de fluidos uma vez que nem todos os parâmetros se encontraram na faixa funcional ideal. O torneamento em material endurecido induziu tensão de compressão nas camadas das amostras cementadas, cuja condição original era tensão residual de tração. Não foram detectadas alterações expressivas na camada cementada, principalmente na região limítrofe da área transversal com a superfície devido ao aquecimento e rápido resfriamento imposto pelo processo de usinagem.
The aim of the present work is to provide relevant information regarding the obtained surface integrity during hard turning process of mechanical components manufactured from case hardened steel ABNT 8620 (DIN 21 NiCrMo 2). The sample residual stress analysis has been experimentally conducted by the incremental Blind Hole method, in which a small hole is machined on the surface of the component and the relieved deformation is recorded through special strain gages, and by the X-ray diffraction technique. The surface was examined by parameters obtained from the surface topography three-dimensional mapping with a laser interferometer instrument. The selected roughness parameters analysis intends to have a functional characterization such as bearing capacity, fluid and lubricants retention ability and contact wear resistance. In the search for altered material layers beneath the surface, metallographic studies were carried out. The functional bearing area curve analysis parameters indicated that the resulting surface has a good area contact, good bearing capacity and reasonable ability to fluid retention as the reduced valley depth parameter did not produced negative values for all conditions tested. The hard turnig process was able to add compression residual stress condition at the surface, and no significant changes were found at the case hardened layer due to rapid heating and cooling imposed by the hard turning process.

O presente trabalho avaliou o efeito de tratamentos térmicos ou diferentes graus de deformação plástica na transformação da austenita do microconstituinte AM de uma chapa de aço alta resistência baixa liga (ARBL) classe API 5L X80 usada para gasodutos. A chapa tem espessura de 19 mm e passaria pelo processo de conformação UOE, mas a deformação foi realizada por laminação a frio, a temperatura ambiente, com reduções de 5 a 20%. O propósito foi compreender melhor o microconstituinte AM, explorar a transformação martensítica induzida por deformação (SIMT) e a decomposição austenítica por tratamento térmico, com ênfase em seu comportamento magnético. A transformação da austenita foi acompanhada através de medidas de polarização magnética, comparada com a densidade de massa e difração de raios X. A deformação plástica e os tratamentos térmicos alteraram a polarização magnética de saturação e a densidade de massa da amostra de aço de forma compatível com a eliminação da austenita retida metaestável. O método de densidade hidrostática foi considerado sensível para mensurar transformações de fase. Os dados obtidos revelam expansão volumétrica de aproximadamente 0,13%, correspondendo a 3,2% a quantidade de austenita retida original do material, enquanto os valores obtidos por polarização magnética de saturação são 2,8% pelo histeresígrafo e 2,1% por MAV. A difração de raios X nas amostras sob deformação ou tratamentos térmicos resultaram em queda nos primeiros picos da austenita quando comparadas com a amostra como recebida.
This study evaluated the effect of different degrees of plastic deformation or heat treatment on the transformation of austenite into martensite of an HSLA steel plate API 5L X80 for pipelines. A 19 mm thickness plate would be submitted to UOE forming process, but the cold work instead occurred by cold rolling at room temperature, with reductions of 5 up to 20%. The purpose was to better understand the MA constituent, explore the strain-induced martensitic transformation (SIMT) and austenitic decomposition by heat treatment with emphasis on its magnetic behavior. The transformation was accompanied by saturation magnetization measurements, compared with the mass density and X-ray diffraction. The plastic deformation or the heat treatment altered the saturation magnetization and the mass density in a manner consistent with the elimination of metastable retained austenite. The density method is sensible to measure phase transformations induced by strain. The data obtained shows a volumetric expansion of about 0.13%, corresponding to an amount of retained austenite of the original material of 3.2%, while the values obtained by magnetization saturation are 2.8% by hysteresigraph and 2.1% by VSM. By X-ray diffraction there is a clear drop in first peaks of austenite of the samples under deformation or heat treatment compared with the sample as-received.

The topic of the Diploma thesis is a design of the New train station in Brno. The plot is located on the boundary of three city districts – Komárov, Štýřice and Trnitá. This area includes the railway structure for the new train station and also its public spaces, which are very close to the river Svratka. The railway structure is designed as bridge construction, that rises all platforms and rail tracks to 7,65 metres above the ground level. So all of the railways do not become a barrier in the city. The main concept extends a longitudinal axis of the city boulevard through the train station, which creates a high-rise building in the southern part of the plot. This axis is written not only to the layout but also to the roof design. The train station includes two underground levels, ground floor and first floor. Underground levels consist of P+R parking, deliveries only area, technical facilities and subway terminal. The ground floor is the main traffic centre. There is an entrance hall, shopping area, bus terminal and public corridors. The first floor includes platforms for train departures and arrivals. There are also public spaces in the entrance hall. The basic structural system consists of two parts. The first part is a massive reinforced concrete structure of the railway bridge deck and all underground levels. This structure is based on reinforced concrete foundation pads with drilled piles. The second part is a steel frame structure of the roof. That includes steel columns and truss girders for the structure of the lower area. The higher part of the roof is designed as a steel-truss bridge with the characteristic profile. The new train station supposes to create a new gate to the city of Brno, that connects contemporary districts with the historical city center.

The topic of the diploma thesis is the design of a new Brno main railway station in the position "The River" (Ac), which was selected from several variants of the reconstruction of the Brno railway junction (ŽUB). The aim of this work is to create an architectural and urban concept, the function of which will be an important contribution to the development of the city of Brno, improving the traffic situation and comfort of the general public or residents of the new adjacent district Trnitá. The solved area is located in the cadastral area of Komárov, Štýřice and Trnitá. The height dominant is represented here by the Europoint building (115 meters). It is located in the axis of the new boulevard, at the other end of which we can see the picturesque Petrov. The main entrance glass hall is adjacent to Europoint. Public facilities are located in the front station area. North of Europoint, it is a smaller building with the function of start-up workshops and offices. Towards the river there are the pre-station square and the public transport terminal. The last building is a hotel with leisure activities. The end of the pre-station area by the river is designed with a park arrangement. It is important to connect to the bike path leading along the river. The river is widened at this point and a smaller accessible island is inserted into it. The new railway body is determined by the binding base of SŽDC, which contains the track on the embankment and on the bridge structure at the level of 7,1 meters above the level of the surrounding terrain. The solved part is bounded by two embankments, which will probably be created as massive reinforced concrete walls. The bridge structure lying between these embankments has dimensions of approximately 154x368 meters, which corresponds to the area of 8 football fields. The bridge deck will be drawn on columns of the given raster. The basic principle in the design of the new main station is simplicity, readability and functionality.

M.Ing.
The aim of Spoornet is to provide a minimise predictable service. In order to provide a predictable service, it is necessary to move trains safely and effectively from the place of departure to their destination. The keywords here are safely and effectively. Although support functions such as infrastructure and train control procedures are vital in moving the train, the train or rolling stock as it is generally known, warrants some attention. Defects on the rolling stock are very costly to Spoornet. This is mainly due to the fact that a defect on the rolling stock that goes undetected can cause damage to the rolling stock and the infrastructure. This damage can eventually lead to derailments. Considering that a derailment can cost Spoornet millions of rand and cause delays to the services, it is only logical to spend time preventing derailments. It is for this reason that a workgroup was formed to investigate and solve the problem of defects causing derailments and delays by developing an early warning system. The need for an integrated train condition monitoring system became apparent when considering an early warning system. The objectives of the integrated train condition monitoring system are to provide train condition information to different users, and alarms on detection of emergency or dangerous conditions. Various train defects that may cause damage or derailments were identified. One of them being a flat wheel on a rail vehicle. A flat wheel is characterised by the flattening of the wheel on one or more positions on its circumference, so that the wheel does not have an even and completely round profile. Flat wheels are mostly caused by the wheels of a vehicle becoming locked during braking, and sliding along the rail track. The friction created by this action grinds a flat spot on the wheel. The flat wheel leads to a decline in the riding quality of the rolling stock and a rise in the levels of vibration and noise is evident. But more importantly, the flat spot causes the wheel to roll unevenly, creating impacts on the rail on some points. It is these impacts that can cause damage to the rail and the rolling stock. Depending on the length of the flat spot, the vehicle type and speed, the stresses may be sufficient to cause final failure of the rail or initiate fatigue cracks in the rail. Severe flat wheels are a safety hazard and can in some cases, cause derailments and consequent delays to trains. Smaller flat spots contribute to track deterioration and so increase maintenance costs by damaging the rails, sleepers and ballast. Flat wheels can thus be very costly to Spoornet and its public image. In addition to safety and economic considerations, wheel flats reduce the comfort levels in the passenger coaches and the noises they make is annoying. In an attempt to restrict the damage caused by flat wheels, most railway administrations place a limit on the length of the flats that may stay in service. But to effectively find a flat wheel on rolling stock is currently a very expensive exercise. Flat wheels can be detected by an audible knocking sound when standing next to the rail. This sound is impossible for the driver to hear and therefore goes undetected. Normally flat wheels are detected by random inspection of the rolling stock or when they are brought in for a routine service. The service cycle on rolling stock can be up to 24 months in Spoornet. Considering that a flat wheel has an impact roughly every 3m, a serious flat generates roughly 160 000 impacts on a single trip on the coal heavy haul export line. It is therefore clear that a flat wheel can cause a considerable amount of damage between service cycles. The severity of the problem is however not accurately defined in Spoornet, because up to a few months ago there was no detection system in use to determine the distribution of flat wheels. The research department of the Deutsche Bundesbahn however considers rail fractures due to the flat wheels to be a serious problem with a significant annual replacement cost. There are thus sound safety and economic reasons for wishing to understand the mechanisms of flat wheels and to develop an early warning system using an automatic detector.

碩士
華梵大學
機電工程學系博碩專班
97
The Taipei metros are powered by dc power, with their positive terminals connected to the collector and their negative terminal connected to the track. Each depot utilizes an electric isolation switch to insulate from the main line tracks to prevent stray currents efficiently. However, different earth systems exist between the main line and the depot tracks. When the metros are dispatched, some of their steel wheels step over both systems’ tracks simultaneously and generate electric arc currents due to the potential differences, in turn causing track corrosions and clamping IRJ (Insulating Rail Joint) flamed. In this condition, the main line tracks and the depot tracks are shorted to issue false alarms signaling the tracks are occupied. Hence, track corrosions are significantly related to the existing potential differences between the two different earth systems when the wheels are crossing the two systems. The author established a Taipei MRT system circuit model, and implemented measured potential differences of all the tracks into the model to carry out necessary simulations. Then, the simulation results verified the experimental data and assured the researchers of the circuit analysis, which is employed to solve the the track corrosion problems. Suggestions to improve the MRT boundary track corrosion conditions between the main line and depot track systems are as following: (1) Change the depot track road bed design from ballast material to concrete material, and it would significantly improve the insulation factor. (2) Rearrange the main line work schedule to dispatch the metro from or to the depots, and it should avoid metro dispatching when suddenly raised potential differences between the tracks and the earth occur. (3) Set up ARC suppressive equipments at the IRJ locations with the devices exercised ahead of the depot dispatching the metros in and out, and the designed snuffers should quench the arcs to improve the IRJ damage conditions efficiently. Keywords: MRT, track, electric corrosion, IRJ.

碩士
華梵大學
機電工程研究所
95
The aim of this paper is to analyze the static stress for the defective steel-rail and wheel in contact using the finite element method. The riding quality, safety, and stability depend on the contact design of wheel and steel-rail. The crack defects exist in the steel-rail due to the manufacturing process will decrease the strength of the rail. The strength of the steel-rail must be large enough to prevent the yielding and fracture. The model of steel-rail and wheel was constructed by using the graphic software, Solid Works. The finite element software, ANSYS, was employed to calculate the stress distribution. The contact effect between the wheel and steel-rail was considered. Many kinds of cracks exist in the rail were simulated in this study. It was found that the maximum equivalent stress of the defective steel-rail is greater than that of the steel-rail free from the crack defects. The stress concentration exists in the crack tip, which will cause the crack to extend unstably. Finally, the influence of the drilling hole on the steel-rail was also studied. It was found that the stress concentration exists in the hole boundary, in which a crack defect may be initiated.

博士
國立臺灣科技大學
電機工程系
105
The current braking devices of trains have not only braking function but also recycling power function in some trains. The functions to prevent the derailment of rail trains and slip between wheels and rails and to increase the climbing force is still not perfect. In order to improve the above-mentioned functions and increase traffic safety, this dissertation proposes the use of physical properties of magnetic components not to damage the wheels and rails. The electromagnetic components set on the bogie axle. The use of circuit loop drives voltage and current. The front and rear wheels produce magnetic force. This dissertation study attractiveness and beating frequency between steel wheels and rails to reduce the derailment rate and the braking distance. The results of this study show that the braking distance can be shortened and the wheel-rail slippage and coasting can be reduced. Finally, the reduction of the beating frequency between the wheels and rails is verified by the neural network experiment.From the verification, it can be seen that the reduction of the beating frequency is in good agreement with the actual test results. This dissertation can significantly improve traffic safety and reduce personal injury and financial losses.