Дисертації з теми "High carbon steel"
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1
Kim, Bae-Kyun. "High temperature oxidation of low carbon steel." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19519.
Анотація:
The quality of steel may be seriously affected by the surface defects that appear on slab surfaces after hot rolling. These defects are related to iron oxidation and, in order to reduce the occurrence of these defects, it is necessary to better understand the formation of iron oxides during high temperature oxidation and the oxide descaling mechanisms. However, systematic research tools and experimental strategies for addressing these issues have not yet been developed. In addition, the mechanisms of oxide cracking and failure have not been understood. In this thesis, research tools and strategies are proposed for studying the high temperature oxidation of low carbon steels. These tools allow the presentation of new data on the phase composition of iron oxides at elevated temperature, characteristics of iron oxide formation, oxide microstructure and texture, oxide defects, and stress distributions in different oxide layers, as well as residual stresses. The microscopic model that was proposed for description of oxide failure allows better understanding of the mechanism for surface defect formation during hot rolling. To describe the dynamics of phase composition changes in textured oxides at elevated temperature, a new phase analysis method is proposed. This x-ray diffraction phase analysis is based on the Rietveld and Dickson's methods, and is used for investigating the effect of alloying elements on the oxidation process. This method was also adopted to track in-situ phase composition changes during high temperature oxidation of commercial low carbon steels. The structure of oxides on low carbon steels, pure iron, and Si-steels was systematically examined by orientation imaging microscopy (OIM). It is demonstrated that OIM can be an invaluable tool for visualizing the oxide microstructure texture and studies of oxide defects. In order to simulate industrial hot rolling of oxidized steel sheet, high temperature oxidations tests were made in the tube furnace up to 950°C, in air. The oxidation process and microstructure development were described using OIM maps including image quality (IQ) and inverse pole figure (IPF) maps. The three different iron oxides phases could be distinguished and the characteristics of oxides with different oxidation histories were compared. Iron oxides developed during high temperature oxidation consisted of wustite (FeO), magnetite (Fe304), and hematite (Fe20s) structures with varying texture, grain shape and size. In order to understand the mechanical properties of iron oxides, residual stresses in the three iron oxides phases were assessed using a specially designed x-ray stress measurement system. The stress distributions in the oxide layers were also simulated using finite element simulation of the hot rolling process.
2
Paul, Graeme William Alexander. "Strain aging of high carbon steel wire." Thesis, University of Strathclyde, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366744.
3
Kuno, Masato. "Fretting damage of high carbon chromium bearing steel." Thesis, University of Nottingham, 1988. http://eprints.nottingham.ac.uk/13207/.
Анотація:
This thesis consists of four sections, the fretting wear properties of high carbon chromium bearing steel; the effect of debris during fretting wear; an introduction of a new fretting wear test apparatus used in this study; and the effects of fretting damage parameters on rolling bearings. The tests were operated under unlubricated conditions. Using a crossed cylinder contact arrangement, the tests were carried out with the normal load of 3N, slip amplitude of 50µm, and frequency of 30Hz at room temperature. The new fretting wear test rig consists of a sphere-on-plate arrangement, and the normal load and slip amplitude were variously changed. Using the new test rig, the tests were performed both at room temperature and 200℃, and tensile stresses were applied to the lower stationary specimens during the fretting wear tests. In the fretting wear tests after tempering at 200,230,260 and 350℃ in air, the high carbon chromium bearing steel showed low coefficients of friction due to a glaze type oxide film. In the fretting wear tests at 200℃, a very low coefficient of friction was obtained. Consequently, the oxide films on high carbon chromium bearing steel tempered at 200,230,260 and 350℃ were thought to be protective in fretting damage. Fretting wear volumes were measured using different specimen combinations and fretting oscillatory directions relative to the axes of the cylindrical specimens, although of the same material couples. It has been found that fretting wear volume is significantly governed by frictional energy (fretting damage per unit area) and frequency of metal-to-metal contact, as determined by electrical contact resistance measurements. Metal-to-metal contact was observed throughout the whole stage of fretting wear even in the case of full slip fretting wear. Fretting crack initiation is encouraged but fretting crack propagation rate is not significantly affected by high normal loads. Compressive residual stresses in the subsurface have little influence on crack initiation, but have a large influence on crack propagation rate. In the study of fracture induced by fretting wear, a critical slip amplitude which led to the shortest fracture life was identified. With the critical slip amplitude (35 µm), a higher coefficient of friction was obtained, and this result suggested a significant effect of coefficient of friction on fracture induced by fretting wear (or fretting fatigue). The mechanisms of fretting wear and fretting fatigue were also discussed. Fretting wear is predominantly governed by the total tangential shear strain due to fretting oscillation. In contrast, fretting fatigue is dominated by the maximum alternating tangential shear strain energy. As coefficient of friction affects significantly both the total tangential shear strain and the maximum alternating tangential shear strain energy, it is thought to be the most important factor which needs to be controlled to reduce damage by both fretting wear and fretting fatigue.
4
Sung, Pil Kyung 1961. "Segregation and structure in continuously cast high carbon steel." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277066.
Анотація:
After hot rolling, the presense of segregation in the center of wire-rod can lead to a nonuniform transformation, resulting in bands of martensite in the microstructure. This is considered to be a defect, called center-martensite, because it can cause cracks and breaks during wire drawing. To identify the mechanism for the formation of center-martensite in wire-rod, the structure, macrosegregation and microsegregation in unworked billets were characterized. Based on measurements of secondary dendrite arm spacings, cooling rates during solidification were estimated. It appears that the macrosegregation of carbon and manganese in the billets manifests itself as the microsegregation in wire-rod, which is an agent in forming the center-martensite. Thus, electromagnetic stirring is proposed as a means to reduce the macrosegregation in the billet and, thereby, reduce the occurrence of center-martensite in wire-rod.
5
Steiner, J. L. d'E. "High carbon stainless steels for petrochemical steam reformers." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355861.
6
Crowe, David Charles. "The high temperature electrochemical behavior of carbon steel in alkaline sulfide solutions." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25567.
Анотація:
The high temperature, high pressure electrochemical behavior of A516 Gr. 70 carbon steel in aqueous alkaline sulfide solutions was studied by means of polarization tests and cyclic volt-ammetry. The effects of variation of temperature (90-150°C), sulfide concentration (0-3 m), scan rate (1-50 mV/s) and scan range, and the effects of stirring and polarization at the switching potentials between scans were investigated. Passivation was consistent with formation of a protective Fe₂O₃ film. An understanding of the electrochemical behavior of iron in the alkaline sulfide solutions was facilitated by the construction
of E-pH diagrams for S-H₂0 and Fe-S-H₂O systems at 25, 100 and 150°C. Sulfide, S²-, currently considered to be stable only at extremely high pH, was excluded from the E-pH diagrams. Reference electrodes, compatible with sulfide solution, were designed for use with an autoclave. The response of the Ag/Ag₂S electrode (SSSE) to variation of temperature, sulfide and hydroxide concentration, and chloride addition was studied. Liquid junction potential and thermal liquid junction potential corrections were applied. The SSSE was not reliably predictable thermodynamically, but was stable and was proven effective in the polarization study. The electrochemical potentials of inert metal reference electrodes, Hg and Pt, were found to be consistent with the mixed potential between polysulfide Sײ⁻, and thiosulfate, S₂O₃²⁻. The Tafel slopes from anodic polarization curves of Pt in alkaline sulfide solutions were consistent with oxidation of HS⁻ to S₂0₃²⁻ at the mixed potential. At more noble potentials, oxidation to polysulfide occurred. Reaction path mechanisms were proposed. Understanding of sulfide oxidation aided in interpretation of the electrochemical behavior of steel in the alkaline sulfide solutions.Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate
7
Massé, Thomas. "Study and optimization of a high carbon steel flat wires." Paris, ENMP, 2010. http://www.theses.fr/2010ENMP1672.
Анотація:
Cette thèse porte sur la modélisation par éléments finis des procédés de mises en forme à froid, que sont le tréfilage et le laminage. Tout d'abord le comportement mécanique des aciers haut carbone a été mesuré grâce à une large campagne d'essais expérimentaux tout au long de cette gamme de mise en forme et une progressive anisotropie mécanique a été observée au cours du tréfilage. Puis, la simulation numérique du tréfilage et du laminage a été réalisée à l'aide de FORGE2005®. Le résultat principal concerne la prédiction de l'élargissement en fin de laminage qui est très imprécise avec une loi isotrope (sous estimation de la largeur de 10%). Cette sous-estimation passe à 5% avec une loi de comportement anisotrope. Ensuite, une troisième partie a porté sur l'étude microstructurale couplée à une analyse des mécanismes d'endommagement des aciers perlitiques au cours du tréfilage et du laminage. L'anisotropie mécanique provient de l'alignement des colonies de perlite au tréfilage et par l'apparition d'une orientation cristallographique préférentielle. Trois mécanismes d'endommagement ont pu être identifiés au cours du tréfilage. Lors du passage au laminage, les cinétiques de propagation de l'endommagement sont modifiées. La simulation a permis d'apporter des informations supplémentaires et de valider les observations expérimentales. Enfin, des calculs d'optimisation du tréfilage ont été effectués et ont permis d'étudier la sensibilité des fonctions objectifs (endommagement et force de tréfilage) aux paramètres d'optimisation (géométrie de filière). De plus, cette étude a mis en évidence que les solutions optimales diffèrent en fonction du choix de la fonction coût et qu'il est possible de diminuer l'endommagement sans trop augmenter la force de tréfilage et le risque de ruptureThis thesis deals with the numerical simulation of cold forming processes, i. E. Wire drawing and rolling. First, high carbon steel mechanical behaviour was measured from experiments throughout this range of steel forming and a progressive mechanical anisotropy has been observed during drawing. Secondly, numerical simulations, with FORGE2005®, have been run to simulate the material behaviour during wire drawing and rolling. The main results show that the widening prediction, with an isotropic behaviour law, is not accurate with an underestimation of 10% on the total width. This underestimation is only 5% when an anisotropic behaviour is used. Then, a microstructural study coupled with an analysis of damage mechanisms was done on high carbon pearlitic steels during wire drawing and rolling. The mechanical anisotropy comes from the orientation of the pearlitic colonies in the drawing, and by the emergence of a preferential crystallographic texture. Three damage mechanisms have been identified during drawing. During rolling, damage expansion kinetics are changed because of heterogeneous strain. Simulation enabled to bring further information and to validate previous experimental observations. Finally, drawing optimization calculations have been performed and enabled to study the sensitivity of the cost functions (damage and drawing force) to optimization parameters (drawing die geometry). Moreover this study highlighted that optimal solution depends on the choice of the cost function and identified an opportunity to reduce damage by reducing the die angle without increasing the axial stresses and the fracture risk
8
Fang, Haitao. "Low Temperature and High Salt Concentration Effects on General CO2 Corrosion for Carbon Steel." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1163794555.
9
Dixon, Philip R. "The thermomechanical properties of 224-carbon steel at high strain rates." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/6821.
10
Olsson, Sara, and Linn Efsing. "Wear testing of high-alloy carbon steel used in mining tools." Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-124595.
Анотація:
Wear is a commonly occurring degradation mechanism for materials and components in the rock drilling industry. The wear can occur by either abrasion or adhesive wear. Further corrosion and presence of water or other lubricating fluids with or without particles may influence the behavior. Which mechanism, or mechanisms, and under which conditions it occurs, as well as the relative wear rate is dependent on the actual operating conditions for the component. In the present study, commonly available and general test methods for wear on high-alloy carbon steel has been analyzed. The project has been carried out through literature reviews and study visits at the tribology laboratory at KTH and at the Angstroms laboratory at Uppsala University. The present study indicates that it is difficult to suggest a feasible test method that is possible to use for all different situations of the wear that may occur. A test adapted to the actual situation is required to achieve a proper wear rate comparable to the wear rate in a real application. According to the requirements from Ovako AB, a test that is general, cost effective and can be used when developing steel with higher wear-resistance, following wear testing methods has been compared: a pin-on-disk apparatus, a dry/wet sand/rubber wheel, a dry/wet sand/steel wheel, a tumbling mill, a particle erosion rig, a solid particle impingement using gas jets and a grinding machine. The tumbling mill, the grinder and the “Standard Test Method for Wear Testing with a Pin-On- Disk Apparatus” correspond to the requirements best. Ovako AB is recommended to continue the work with these testing methods.Nötning är en vanlig mekanism som orsakar nedbrytning på material i gruvindustrin. Nötningen kan förekomma som abrasiv eller adhesiv nötning. Korrosion och närvaro av vatten eller andra smörjande vätskor med eller utan lösa partiklar kan påverka beteendet. Den eller de mekanismer som styr nötningen såväl som nötningstalet beror på de aktuella förhållanden vilka materialet eller materialen verkar i. I denna studie har en generell testmetod för att utvärdera nötning på höglegerat kolstål har undersökts. Arbetet har genomförts genom litteratursökning samt studiebesök vid tribologiska laboratoriet på KTH samt på Ångströmska i Uppsala. Utifrån arbetet har det visat sig att det inte förekommer några generella nötningstest för alla applikationer, då det krävs ett test som är anpassat efter verkligheten för att få ut korrekt nötningstal. Utifrån Ovako ABs önskemål om ett generellt test som är ekonomiskt hållbart samt kan användas för att utveckla nötningsbeständigheten i de stål där nötning förekommer har följande testmetoder jämförts: pinne/skiva-maskin, blött/torrt sand/gummihjul, blött/torrt sand/stålhjul, roterande trumma, ”Erofugen”, partikelsprutare och en slipmaskin. De test som motsvarar kravprofilen bäst är den roterande trumman, slipmaskinen samt den standardiserade pinne/skiva-maskinen. Utifrån dessa testmetoder rekommenderas Ovako AB att fortsätta arbetet.
11
Qu, Hao. "ADVANCED HIGH STRENGTH STEEL THROUGH PARAEQUILIBRIUM CARBON PARTITIONING AND AUSTENITE STABILIZATION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1346250505.
12
Qu, Hao. "Advanced High Strength Steel Through Paraequilibrium Carbon Partitioning and Austenite Stabilization." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283353953.
13
Peiris, Nisal Abheetha. "STEEL BEAMS STRENGTHENED WITH ULTRA HIGH MODULUS CFRP LAMINATES." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/204.
Анотація:
Advanced composites have become one of the most popular methods of repairing and/or strengthening civil infrastructure in the past couple of decades. While the use of Fiber Reinforced Polymer laminates and sheets for the repair and strengthening of reinforced concrete structures is well established, research on the application of FRP composites to steel structures has been limited. The use of FRP material for the repair and rehabilitation of steel members has numerous benefits over the traditional methods of bolting or welding of steel plates. Carbon FRPs (CFRPs) have been preferred over other FRP material for strengthening of steel structures since CFRPs tend to posses higher stiffness. The emergence of high modulus CFRP plates, with an elastic modulus higher than that of steel, enables researchers to achieve substantial load transfer in steel beams before the steel yields.
This research investigates both analytically and experimentally, the bond characteristics between ultra high modulus CFRP strengthened steel members and the flexural behavior of these members. A series of double strap joint tests with two different CFRP strip widths are carried out to evaluate the development length of the bond. Both ultra high modulus and normal modulus CFRP laminates are used to compare strengthened member performance. Steel plates reinforced with CFRP laminates on both sides are loaded in tension to evaluate the load transfer characteristics. Debonding under flexural loads is also studied for ultra high modulus CFRP strengthened steel girders. Flexural tests are carried out under 4-point bending on several small scale wide flange beams. This study also introduces the novel ultra high modulus CFRP plate strip panels for strengthening of steel bridge girders. The first field application of ultra high modulus CFRP laminates in strengthening steel bridge girders in the United States is also carried out as part of the research. Full scale load tests carried out before and after the strengthening are utilized to measure the degree of strengthening achieved and checked against the expected results. A finite element model is developed and calibrated using data obtained from the field testing of the bridge. The model is then used to evaluate the behavior of the bridge under different conditions before and after the strengthening process.
14
Schnerch, David. "Strengthening of Steel Structures with High Modulus Carbon Fiber Reinforced Polymer (CFRP) Materials." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-06152005-090112/.
Анотація:
Transportation departments and the telecommunications industry are currently demanding cost-effective rehabilitation and/or strengthening techniques for steel structures, including bridges and monopole towers. Rehabilitation is often required due to cross-section losses resulting from corrosion damage and strengthening may be required due to changes in the use of a structure. Current strengthening techniques, have several disadvantages including their cost, need to match the surface configuration of the existing structure, poor fatigue performance and the need for ongoing maintenance due to continued corrosion attack. The current research program makes use of new high modulus types of carbon fiber for strengthening steel structures. The experimental program was developed in four phases. These phases included the selection of suitable resins and adhesives for bonding the CFRP sheets and strips to the steel, characterization the bond to the steel through testing of the development length, performing large-scale tests on strengthened steel monopole towers and also determining the behavior of strengthened steel-concrete composite beams that are typical of bridge structures. The result of the experimental program was the demonstration of sizeable strength and stiffness increases for the steel structures, strengthened with the developed system. Analytical work has also been completed to predict these strength and stiffness increases as well as to determine the bond stresses to ensure the avoidance of a debonding failure, which is detrimental to the effective use of the high modulus CFRP material.
15
Rosli, Nor Roslina. "The Effect of Oxygen in Sweet Corrosion of Carbon Steel for Enhanced Oil Recovery Applications." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1448974434.
16
Jauseau, Nicolas. "Multiphase Flow Effects on Naphthenic Acid Corrosion of Carbon Steel." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1354149810.
17
Song, Wenwen [Verfasser]. "Characterization and simulation of bainite transformation in high carbon bearing steel 100Cr6 / Wenwen Song." Aachen : Shaker, 2014. http://d-nb.info/1060622785/34.
18
Yagi, Shunsuke. "Surface modification process for high-purity iron and carbon steel by alternating pulsed electrolysis." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136229.
19
Trueman, Anthony Roger. "Characterization and corrosion studies of high carbon tool steel/tungsten carbide metal matrix composites." Thesis, Queensland University of Technology, 1999.
20
Barnes, Peter Edward. "An investigation into the corrosion fatigue behaviour of high strength carbon steel tensile armour wires." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/an-investigation-into-the-corrosion-fatigue-behaviour-of-high-strength-carbon-steel-tensile-armour-wires(1fdde868-c9b9-424f-a472-5b9c0ae5273e).html.
Анотація:
The corrosion fatigue behaviour of high strength carbon steel tensile armour wires that are used in flexible risers has been explored. An investigation of the corrosion fatigue failure mechanisms for two different sets of corrosion fatigue tested high strength steel wires has been carried out. The two different tensile armour wires were 12 mm x 4 mm and 12 mm x 7 mm. The wires had been corrosion fatigue tested in up to three different seawater environments, namely aerated, CO2 saturated to 1 bar absolute and 100 mbar absolute H2S-CO2 balance to 1 bar absolute. The corrosion fatigue failure investigation included undertaking statistical analysis of fatigue crack and corrosion pit data to establish the effects of environment, applied stress, R-ratio and microstructure due to degree of cold drawing on the corrosion fatigue behaviour. The 12 mm x 4 mm has fine grain martensite-pearlite structure with anisotropic microstructure in the transverse plane. The 12 mm x 7 mm has larger grain martensite-pearlite structure with equiaxed microstructure in the transverse plane. The corrosion fatigue crack path for the two tensile armour wires exhibits transgranular and intergranular cracking due to variations in R-ratio and microstructure. The analysis identified that a significant amount of localised corrosion pitting was present on the surface of both the 12 mm x 4 mm and 12 mm x 7 mm high strength carbon steel tensile armour wires and that many corrosion fatigue cracks had initiated from these geometric discontinuities. A method was developed in order to apply an optical image correlation technique to a sample immersed in seawater. The research has shown that digital image correlation may be applied for in-situ imaging of a corroding and dynamically deforming surface within a seawater environment. The technique demonstrated the establishment of localised surface strain around the corrosion pits during mechanical loading. The results of the surface strain mapping show that the interaction between multiple corrosion pits is consistent with a significant increase in surface strain when compared to a single surface pit acting alone. The results also show that a small single stress raiser can exhibit a high surface stress concentration when compared to a larger one as the strain is dependent upon the geometry of the pit. The highest strain concentration is at the edge of the pit, parallel to the loading direction. The results show the interaction that multiple pits have with each other, the effect they have on surface strains and how they and other types of stress raiser lead to premature failure of components. Further to this the effects of residual stress on crack nucleation were considered. Fatigue cracks initiate at the surface of the high strength carbon steel tensile armour wire therefore surface measurements were carried out to establish the effects of environment and applied load on the development of residual stress fields. The 12 mm x 4 mm wire shows some correlation between applied stress range and surface residual stress measurements with. For the 12 mm x 4 mm wire corrosion fatigue tested in aerated seawater the surface residual stress becomes increasing compressive with an increase in applied stress. For the 12 mm x 4 mm wire corrosion fatigue tested in CO2 saturated seawater the surface residual stress appears to be independent of applied stress. However for the 12 mm x 7 mm carbon steel tensile armour wire there is no correlation between the applied stress range and the surface residual stress. The differences in surface residual stress may be due to the differences in R-ratio, microstructure and level of cold drawing due to the Bauschinger effect. Surface residual stress measurements have been used to explore the effects of the shakedown process on the high strength carbon steel tensile armour wires prior to corrosion fatigue testing. They show that at a high applied stress range the shakedown process readily develops a compressive residual stress on the surface of the carbon steel wire. This is mostly the case for the low applied stress range; however care should be taken when considering the effects of shakedown on a lower stress range in so far as it may not completely remove the tensile residual stress. Through thickness residual stress measurements show a similar distribution of residual stress fields throughout the high strength carbon steel tensile armour wires independent of the applied stress range and environment.
21
Suhor, Muhammad Firdaus. "Effect of Iron Carbonate Deposition on Mild Steel Corrosion in High Partial Pressure Carbon Dioxide Systems." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1532376719359574.
22
Dawood, Mina Magdy Riad. "Fundamental Behavior of Steel-Concrete Composite Beams Strengthened with High Modulus Carbon Fiber Reinforced Polymer (CFRP) Materials." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-06292005-192140/.
Анотація:
There is a growing need for a cost-effective, durable repair system that can be used for the repair and strengthening of steel bridges. Recently, high modulus carbon fiber reinforced polymers (CFRP) have been developed with a modulus of elasticity approximately two times greater than that of steel. Externally bonded high modulus CFRP materials have successfully been used to increase the elastic stiffness and ultimate capacity of steel-concrete composite beams However, since the technology is relatively new, the detailed behavior of steel bridge members strengthened with high modulus CFRP is not yet well understood. The current research investigates three aspects of the behavior of steel-concrete composite beams in detail. An experimental program was conducted to investigate the behavior of steel-concrete composite beams strengthened with high modulus CFRP materials. In the first phase of the study the behavior under overloading conditions was investigated. In the second phase of the research, the fatigue durability of the system was examined. In the third phase, the possible presence of shear-lag between the steel beam and the CFRP materials was investigated in detail. An analytical model was developed which can be used to determine the ultimate capacity and elastic stiffness increase for steel beams strengthened with high modulus CFRP materials. Additionally, a set of criteria are proposed which can be used to determine the allowable increase in the live load level for steel beams strengthened with high modulus CFRP materials.
23
Lyaya, E. C. "Macroscopic and microscopic variation of iron and high carbon steel production in the Southern Highlands of Tanzania." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1398300/.
Анотація:
One essential feature of African iron production process is that it is greatly variable in culture and technology. The early research focused on some themes: origins, culture, and how iron was produced, which were investigated using archaeological, ethno-archaeological, and experimental methods. The purpose of this thesis was to examine the relationship between macroscopic and microscopic variation of iron and steel production in the southern highlands of Tanzania. I used field methods: ethnographic inquiry, surface and sub-surface survey, mapping, and excavation; and laboratory analytical techniques: firing, optical and electron microscopy, microanalysis, and X-ray fluorescence to investigate the research theme. The results indicate that there is a strong relationship between macro- and microscopic variation of iron and steel production in terms of the use technical ceramics with good refractory qualities, the presence of the three stage process in Ufipa and Unyiha, involving a refining stage between the smelting and smithing stages; the liquid slag handling techniques, the reduction efficiency, and the nature of the final products: soft iron and carbon-rich steel. Although there are macroscopic data on the use of forced- and natural-draft furnaces in the region, it is difficult to microscopically verify the air supply mechanisms in the region. This work recommends that in order to avoid the confusion on the three stage process and relationship between macro- and microscopic variation in iron and steel production, the role of matrix and provenance should be given due weight as laboratory analyses.
24
Stanford, Kirk Alan. "STRENGTHENING OF STEEL STRUCTURES WITH HIGH MODULUS CARBON FIBER REINFORCED POLYMERS (CFRP) MATERIALS: BOND AND DEVELOPMENT LENGTH STUDY." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-12202008-112409/.
Анотація:
Cost-effective solutions for the rehabilitation and strengthening of steel structures, such as steel bridges and steel monopole towers used for cellular phone antennas, are greatly needed by government transportation departments and industry. Rehabilitation is often required due to loss of cross-section from corrosion and/or changes of the demand or use of a structure. Current techniques for strengthening steel structures have several drawbacks including requiring heavy equipment for installation, their fatigue performance, in addition to the need for ongoing maintenance due to continued corrosion attack. The current research program proposed the use of a new high modulus carbon fiber reinforced polymer (CFRP) for strengthening of steel structures. This program includes extensive research to select the resin for wet lay-up of carbon fiber sheets and the adhesives for bonding of pre-cured laminate strips. The bond behavior of FRP materials to steel structures is quite different from that of concrete structures. Preliminary test results showed the occurrence of very high bond stresses for most strengthening applications due to the amount of strengthening required for developing the material for steel structures and bridges.
25
Mazidi, Aimal. "Comparison of a new, high precision, energy efficient welding method with the conventional Gas Metal Arc Welding on high carbon steel base metal." Thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-6860.
Анотація:
CMT+P welding is less susceptible to hot cracking than the MAG welding process due to use of low heat input properties. Solidification cracking was found in all weld specimens that had greater 0.39KJ/mm heat inputs. Cracking occurs because of the contraction stresses generates during cooling. Hydrogen cracking is found in HAZ with low heat input parameters, this type of cracking occurred because of very rapid cooling and therefore not enough time to allow the hydrogen to dissipate from the specimen. To eliminate this type of cracking the experiment could be repeated by adding heating during welding to control and reduce the cooling rate. Due to high carbon content in the steel and very fast cooling the microstructure of the weld is martensitic in the base metal as well as the HAZ. Microstructure in the weld and base metal is martensitic due to high carbon con-tent and rapid cooling. At low heat inputs dilution is less and therefore lower carbon content in weld pool. Better weld appearance and weld quality is achieved with CMT+P welding process than the conventional GMA welding processes because of the new wire movement technology during welding
26
Mohamed, Mohd Farid. "Water Chemistry and Corrosion Inhibition in High Pressure CO2 Corrosion of Mild Steel." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1429223819.
27
Haddad, Mike [Verfasser]. "Nanostructure evolution and enhancement of mechanical properties for medium carbon steel through high pressure torsion processing-nanosteels / Mike Haddad." Ulm : Universität Ulm, 2017. http://d-nb.info/1132713080/34.
28
Tran, Tu Anh. "Modelling and experimental study of secondary dendrite arm spacing and micro-segregation in continuously cast high carbon bloom steel." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5635/.
29
Lin, Kaijie. "Development of advanced plasma surface technologies for high performance carbon paper gas diffusion layer and 316 stainless steel bipolar plates." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6351/.
Анотація:
In this work, a portfolio of novel active screen plasma surface engineering technologies have been developed including active screen plasma surface modification of carbon paper for gas diffusion layer (GDL) and active screen plasma surface co-alloying of 316 austenitic stainless steel with both interstitial alloying element of nitrogen and such substitutional alloying elements as silver (Ag), niobium (Nb) and platinum (Pt). The active screen plasma surface modification of GDL carbon paper at a low temperature for a short period of time can effective activate the carbon paper surface mainly due to the removal of the hydrophobic PTFE coating and introduction of many functional groups, thus contributing to the improved growth of Pt nano-wires. Accordingly, the electrochemical and catalysis performance can be effective improved. The novel ASP surface alloying technique developed from this research has been applied to modify the 316 stainless steel surface using nitrogen for active screen plasma nitriding (ASPN); nitrogen and silver (N&Ag); nitrogen and niobium (N&Nb); and nitrogen and platinum (N&Pt). The experimental results have demonstrated that the layer structure of the ASP treated 316 SS surfaces can be tailored by using different alloying elements and/or adjusting treatment parameters. The surface electrical conductivity of 316 can be reduced significantly. The ASPN, ASPA(N&Ag) and ASPA(N&Nb) increase the corrosion potential, lower the corrosion current density, but raise the passive current density of 316 SS. Among all the surface alloying treatments, the ASPA(N&Pt) treatment has delivered the best performance and fulfilled the technique target set by the Department of Energy (DoE), USA.
30
Khusru, Shovona. "High performance hybrid structural column with rubberised concrete under axial compressive loading." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/233665/1/Shovona_Khusru_Thesis.pdf.
Анотація:
Every year millions of tyres are disposed of worldwide in landfill resulting in the rise of an environmental burden. This thesis demonstrates the development of a sustainable novel hybrid double skin tubular column utilizing the scrap tyre rubbers. The proposed column made with rubberised concrete infill, filament wound FRP outer tube and steel inner tube, has been studied extensively through experimental testing, finite element modelling and parametric studies, to understand the structural performance under axial loading. This column, compared to the traditional column will be sustainable and beneficial at the locations demanding improved ductility, energy absorption and corrosion resistance.
31
Agrizzi, Ronqueti Larissa. "Study of grain boundary oxidation of high alloyed carbon steels at coiling temperature." Thesis, Compiègne, 2018. https://bibliotheque.utc.fr/Default/doc/SYRACUSE/2018COMP2405.
Анотація:
Les aciers à haute résistance (AHSS) ont été largement utilisés dans le cadre d’applications automobiles visant à améliorer la sécurité et l’allègement des structures. Afin d'atteindre les objectifs en termes de propriétés mécaniques, ces nouveaux aciers sont composés de teneurs en éléments d’alliages beaucoup plus élevés (par exemple silicium et manganèse) que les aciers usuels. En conséquence, l'AHSS est susceptible de subir une oxydation interne sélective lors du refroidissement des bobines d’acier. L'oxydation sélective interne, en particulier l'oxydation aux joints de grains (GBO), est actuellement l'un des principaux obstacles à la production de ces aciers. Elle réduit le nombre de cycles avant la rupture de fatigue et rend ainsi difficile l’obtention des spécifications du client. Par conséquent, ce travail de thèse était axé sur l'effet de plusieurs paramètres sur le comportement à l’oxydation interne sélective. Parmi eux, l'impact de la décarburation, l'influence de la température de bobinage et de la couche de calamine, l'effet de différentes teneurs en silicium et / ou en manganèse et leur comportement en diffusion. De plus, l'impact de la désorientation des joints de grains sur l'oxydation interne a également été étudié. Des alliages modèles à base de fer binaires / ternaires ainsi que des aciers industriels ont été étudiés via un large ensemble de techniques expérimentales. Ces analyses ont mis en évidence une décarburation stable pour tous les échantillons étudiés qui n'a pas d'impact sur l'oxydation interne sélective pour une longue exposition aux conditions isothermes. Les profondeurs d’oxydation aux joints de grain ont été examinées selon les différentes configurations de tests et se sont révélées sensibles aux teneurs en silicium ou en manganèse. Pour certaines d'entre elles, différents comportements de diffusion du silicium ont été identifiés vis-à-vis de l'oxydation des joints de grains, en fonction des températures. Considérant quelques hypothèses restrictives, l'application de la théorie de l'oxydation interne sélective de Wagner a permis de déterminer le coefficient de diffusion de l'oxygène aux joints de grain. Pour surmonter certaines limites du modèle de Wagner, un modèle d'oxydation sélective a été appliqué pour comprendre l'effet de différents paramètres sur la pénétration de l'oxygène à l'intérieur du métal et principalement sur la profondeur des joints de grain affectée par l'oxydation sélective. Les connaissances acquises à partir de ce travail de thèse aideront à comprendre et à limiter l'oxydation sélective interne (principalement l’oxydation aux joints de grain) dans les aciers avec des compositions complexes en éléments d’alliage. En outre, les résultats peuvent être utilisés pour évaluer les paramètres d’un modèle d'oxydation sélectiveAdvanced high-strength steels (AHSS) have been widely used in automotive industry to improve safety and fuel economy. In order to reach the mechanical properties targets, these new steels are composed by much higher alloy contents (e.g. silicon and manganese) than usual steels. As consequence, the AHSS may suffer of selective internal oxidation during the cooling of hot coil. The selective internal oxidation, especially the grain boundary oxidation (GBO), is currently one of the main obstacles to the production of these steels. It reduces the number of cycles before fatigue failure and thus, makes it difficult to reach the specifications of the customer. Therefore, this PhD work was focused on the effect of several parameters on selective internal oxidation behavior. Among them, the impact of decarburization, the influence of coiling temperature and the mill scale, the effect of different silicon and/or manganese contents and their diffusion behavior. Moreover, the impact of grain boundary misorientation on grain boundary oxidation was also investigated. Either binary/ternary iron-based model alloys as well as industrial steels were investigated by a large set of experimental techniques. This analysis showed a stable decarburization for all investigated samples that does not impact the selective internal oxidation for long exposure time in isothermal conditions. The GBO depths were examined according to the different test configurations and were found dependent for some cases on silicon or manganese content. For some of them, different silicon diffusion behaviors were identified with regards to grain boundary oxidation depending on temperatures. Considering some restrictive hypotheses, the application of Wagner’s theory of selective internal oxidation allowed determining the grain boundary diffusion coefficient of oxygen. To overcome some limitations of Wagner’s model, a model of selective oxidation has been applied to understand the effect of different parameters on the penetration of oxygen inside the metal and principally on the grain boundary depth affected by selective oxidation. The knowledge acquired from this PhD work will help to understand and limit the selective internal oxidation (mainly GBO) in new steels with complex alloy compositions. Furthermore, the results may be used to assess a model of selective oxidation
32
Rodriguez, Alvaro A. "Corrosion inhibition mechanism of a surfactant admixture on carbon steel alloy ASTM A36 [UNS K02600] coated with a high performance UV-cured coating." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460564870.
33
VanTrees, Craig. "Analysis of Precipitates and Waters Associated with an Alkaline Leachate, Gulf State Steel Property, Gadsden, Alabama: A Reconnaissance Study." Digital Archive @ GSU, 2010. http://digitalarchive.gsu.edu/geosciences_theses/25.
Анотація:
Calcite stalactites ranging in length from several inches to a foot long are found forming on the southeastern slag pile at the former Gadsden Steel Mill of the Gulf States Steel Corporation. Analyses of samples collected per EISOPQAM guidelines include the following: petrographic, conductivity, pH, XRD, XRF, TDS, and major cations and anions. Preliminary field pH and conductivity measurements indicate that waters near the slag pile have a pH ranging from 11-12 and a conductivity ranging from 1115-6300 μS/ cm. Titration data indicate that the maximum pH value is 12.5. These calcite stalactites and stream coatings result from the dissolution of the steelmaking slag by rainfall. These alkaline waters precipitate calcite when they are in contact with atmospheric CO2. Improper management of slag products can lead to aesthetically impacted environments and ecosystems. Several studies and this study show that steel slag could be used to sequester atmospheric CO2.
34
Gao, Shujun. "Thermodynamics and Kinetics of Hydrogen Sulfide Corrosion of Mild Steel at Elevated Temperatures." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1528836064560164.
35
Ghasemi, Sahar. "Innovative Modular High Performance Lightweight Decks for Accelerated Bridge Construction." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2248.
Анотація:
At an average age of 42 years, 10% of the nation’s over 607,000 bridges are posted for load restrictions, with an additional 15% considered structurally deficient or functionally obsolete. While there are major concerns with decks in 75% of structurally deficient bridges, often weight and geometry of the deck further limit the load rating and functionality of the bridge. Traditional deck systems and construction methods usually lead to prolonged periods of traffic delays, limiting options for transportation agencies to replace or widen a bridge, especially in urban areas.
The purpose of this study was to develop a new generation of ultra-lightweight super shallow solid deck systems to replace open grid steel decks on movable bridges and as well serve as a viable alternative in bridge deck replacements across the country. The study has led to a lightweight low-profile asymmetric waffle deck made with advanced materials. The asymmetry comes from the arrangement of primary and secondary ribs, respectively perpendicular and parallel to the direction of traffic. The waffle deck is made with ultrahigh performance concrete (UHPC) reinforced with either high-strength steel (HSS) or carbon fiber reinforced polymer (CFRP) reinforcement. With this combination, the deck weight was limited to below 21 psf and its overall depth to only 4 inch, while still meeting the strength and ductility demands for 4 ft. typical stringer spacing. It was further envisioned that the ultra-high strength of UHPC is best matched with the high strength of HSS or CFRP reinforcement for an efficient system and the ductile behavior of UHPC can help mask the linear elastic response of CFRP reinforcement and result in an overall ductile system. The issues of consideration from the design and constructability perspectives have included strength and stiffness, bond and development length for the reinforcement, punching shear and panel action. A series of experiments were conducted to help address these issues. Additionally full-size panels were made for testing under heavy vehicle simulator (HVS) at the accelerated pavement testing (APT) facility in Gainesville. Detailed finite element analyses were also carried out to help guide the design of this new generation of bridge decks. The research has confirmed the superior performance of the new deck system and its feasibility.
36
Sjoberg, Elf Julia, and Espinosa Kristoffer Wannheden. "Carbon capture and utilisation in the steel industry : A study exploring the integration of carboncapture technology and high-temperature coelectrolysisof CO2 and H2O to produce synthetic gas." Thesis, KTH, Energiteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-226729.
Анотація:
The present thesis studies the potential for introducing the technology of co-electrolysis of carbondioxide (CO2) and water (H2O) through a Solid Oxide Electrolyser Cell (SOEC) in a top gas recyclingblast furnace (TGR-BF) in a steel plant. TGR-BF, commonly presented in literature as a promisingcarbon capture and storage (CCS) pathway for the steel industry, can drastically decrease theseemissions by successively recycling up to 90 % of the top gas from a blast furnace (EU, 2014) andsequestering the CO2 from the highly carbon concentrated remaining top gas. Blast furnaces (BF)represent about 20 % of the total carbon dioxide emissions of a steel plant (Carpenter, 2012). Based onthe current research status of SOEC, this report aims at exploring the utilisation of carbon dioxidecaptured from TGR-BF through a simultaneous electrolysis of CO2 and H2O, a novel and highly efficientpathway of producing valuable synthetic gas (syngas), used in chemical and industrial applications.It is important to note that neither of the technologies is yet in commercialisation phase, and that thesuggested installation would presently not be possible, but nevertheless provides an interesting pathwaytowards closing the carbon cycle of steelmaking. To give an idea of the magnitude of the SOECinstallation and its syngas production if combined with TGR-BF, an analysis of existing case studies ofeach technology was made. The SOEC system modelled by Fu et al. (2010) was scaled to fit the CO2emissions of Ruukki Metals steel plant in Raahe, Finland, for which data is abundant and reliable. Tohighlight the integration potential of the two separate technologies, a conceptual process flow chart wasdesigned and a literature review of the respective technologies performed, allowing the identification ofintegration challenges, presented in the analysis. The literature study reveals that challenges for thesystem include: gas purity requirements, gas composition requirements, scalability, life-timecompatibility, plant complexity and high variation of plant infrastructure. In the discussion, difficultiesrelated to a technology shift in a traditional industry are considered. For further research, mathematicalmodelling of thermodynamics of the system as well as an economic assessment are recommended.Följande studie utforskar potentialen att implementera co-elektrolys av koldioxid (CO2) och vatten(H2O) genom en fastoxid elektrolyscell (SOEC) i en masugn där återvinning av masugnsgasen tillämpasgenom s.k. Top-Gas Recycling Blast Furnace (TGR-BF). Masugnen representerar omkring 20 % av detotala koldioxidutsläppen från ett stålverk (Carpenter, 2012) varför TGR-BF i flera studier beskrivs somen lovande teknik för avskiljning och lagring av koldioxid (CCS) i stålindustrin. TGR-BF har potentialenatt drastiskt minska utsläppen genom att återvinna upp till 90 % av masugnsgasen (BFG) och avskiljningav koldioxid från den CO2-rika gasen som återstår. Genom att kartlägga den senaste forskningen inomSOEC och analysera resultat från försöksanläggningar som tillämpar TGR-BF syftar denna studie attutforska möjligheten för ett kombinerat system där koldioxiden från masugnsgasen, genom en simultanco-elektrolys av CO2 och H2O, används för syntesgasproduktion; en viktig gas i många kemiska ochindustriella tillämpningar.Det är viktigt att poängtera att ingen av de två teknikerna idag är kommersialiserade och att enintegration av dessa för tillfället därför inte är genomförbar, men att studien tillhandahåller en intressantmöjlighet för minskade koldioxidutsläpp för stålindustrin. För att undersöka skalbarheten mellan de tvåteknikerna genomfördes en fallstudie på Ruukki Metal’s stålverk i Raahe, Finland kombinerat med ettSOEC-system som tillämpats av Fu m.fl. (2010) i deras modellering av syntesgas genom co-elektrolys.Fallstudien uppskattar att 2838 ton syntesgas per dag skulle kunna produceras från den infångadekoldioxiden i stålverket Raahe, Finland. Ett konceptuellt flödesschema utformades för att åskådliggöraintegrationspunkterna för de två teknikerna. En litteraturstudie gjordes i syfte att förstå vilka utmaningaren sådan integration skulle innebära. Dessa utmaningar, tillsammans med utmaningar för de två enskildateknikerna, presenteras i analysen. Litteraturstudien påvisade att utmaningar för det integrerade systemetinkluderar: krav på gasernas renhet samt sammansättning, systemens skalbarhet, livstid samtkomplexiteten och variationen mellan olika stålverk. Analysen och diskussionen behandlarsvårigheterna med stora teknikskiften i en traditionell industri. För vidare studier rekommenderas enmatematisk modellering av systemet där termodynamiska och ekonomiska aspekter behandlas.
37
Behrani, Vikas. "Surface Modifications of Steels to Improve Corrosion Resistance in Sulfidizing-Oxidizing Environments." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19708.
Анотація:
Industrial and power generation processes employ units like boilers and gasifiers to burn sulfur containing fuels to produce steam and syn gas (H2 and CO), which can generate electricity using turbines and fuel cells. These units often operate under environments containing gases such as H2S, SO2, O2 etc, which can attack the metallic structure and impose serious problems of corrosion. Corrosion control in high temperature sulfur bearing environments is a challenging problem requiring information on local gaseous species at the surface of alloy and mechanisms of degradation in these environments. Coatings have proved to be a better alternative for improving corrosion resistance without compromising the bulk mechanical properties. Changes in process conditions may result in thermal and/or environment cycling between oxidizing and sulfidizing environments at the alloy surface, which can damage the protective scale formed on the alloy surface, leading to increase in corrosion rates. Objective of this study was to understand the effect of fluctuating environments on corrosion kinetics of carbon steels and develop diffusion based coatings to mitigate the high temperatures corrosion under these conditions. More specifically, the focus was : (1) to characterize the local gaseous environments at the surface of alloys in boilers; (2) optimizing diffusion coatings parameters for carbon steel; (3)understand the underlying failure mechanisms in cyclic environments; (4) to improve aluminide coating behavior by co-deposition of reactive elements such as Yttrium and Hafnium; (5) to formulate a plausible mechanism of coating growth and effects of alloying elements on corrosion; and (6) to understand the spallation behavior of scale by measuring stresses in the scales. The understanding of coating mechanism and effects of fluctuating gaseous environments provides information for designing materials with more reliable performance. The study also investigates the mechanism behind the effect of REs on scale adhesion and sulfidation behavior. Thus, the present work will have a broad impact on the field of materials and coatings selection for high temperature industrial environments such as boilers and gasifiers, and provides information on RE-modified aluminized coatings on carbon steel as an alternative for the use of bulk superalloys under high temperature sulfur bearing environments.
38
Ng, Eric Eng Seng. "Laser welding of high carbon steels." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/2143/.
Анотація:
Laser welding, unlike conventional arc or gas welding, can be effectively utilised to produce high quality, clean and tough welds in high carbon steels. Results of welding high carbon steel are presented. The weld characteristics related to the fast cooling rate were critically evaluated and methods to reduce the rate of cooling were developed. The grain size produced in the fusion and narrow heat affected zones significantly affected the mechanical properties of the welded joint. Three lasers were used: Nd:YAG, CO2 and a high power laser diode (HPDL). The investigations were carried out using a pulsed, 400 W, Nd:YAG laser, a CW, 1.2 kW, CO2 laser and a CW, 1.4 kW high power diode laser. For the Nd:YAG laser, the dual beam delivery system was achieved with a step index fibre to produce in-line process heat-treatment during welding. The spatial and temporal temperature distribution was controlled in the weld region to generate the desired mechanical properties, without losing the benefits of this low distortion joining process. For the CO2 laser system, a dual beam system was successfully designed, fabricated and the performance of the multiple beam system was evaluated. The welding quality was characterised by quantifying the effect of different laser parameters and welding geometry, including flat, angular, clamped and unclamped. The welding performance of the Nd-YAG laser was dependent on the welding speed, pulse width and pulse repetition frequency (PRF). The effect of varying the laser parameters was quantified by measuring the hardness profiles, tensile strength, weld width, weld penetration and the rare of weld volume formation. Furthermore, microscopic examination was conducted at the welded joint. The quality of the welds was improved by increasing the pulse width and pulse repetition frequency (PRF), achieving a deeper penetration, wider weld width and greater weld volume formation rate and a tougher weld. At a slower welding speed, and for the higher pulse width and PRF, the hardness profiles were greatly reduced due to the greater spatial overlap of laser beam on the workpiece.
39
Pu, Xiaoxue. "Thermomechanical study of the gigacycle fatigue behavior of pure iron and carbon-manganese steels : influence of chemical composition and microstructure on damage and crack initiation mechanism." Thesis, Paris 10, 2019. http://www.theses.fr/2019PA100051.
Анотація:
Ce travail tente de mieux comprendre les dommages par fatigue dans les aciers à ferrite-perlite dans la fatigue à très grand nombre de cycles (VHCF). Les influences de deux paramètres, le pourcentage de phase perlite et le pourcentage d'atomes interstitiels libres dans une solution solide, sont étudiées pour comprendre les mécanismes de dissipation en fatigue à 20 kHz. Une thermographie infrarouge in situ est réalisée pour enregistrer les changements de température, tandis que des observations au microscope sont menées pour étudier le mécanisme de dissipation. Pour les matériaux de BCC, sous fortes amplitudes de contrainte, une augmentation soudaine de la température se produit sans initiation de fissure ni fracture. L’augmentation inévitable de la température jusqu’à des centaines de degrés aux fortes amplitudes de contrainte est principalement due à la mobilité des dislocations vis, qui est l’une des clés permettant d’expliquer le comportement en fatigue observée de la structure du BCC sous un chargement haute fréquence. Par conséquent, les PSB en surface et les micro-vides dans la matrice émergent en masse, accompagnant cette élévation abrupte de la température. Ces phénomènes sont considérés comme une transition du mécanisme de déformation du régime thermique au régime athermique. À faible amplitude, peu de PSB ou de rugosité de surface sont encore observés. Il a été constaté que les PSB sur le fer armco étaient susceptibles d’apparaître avant 1x107 cycles et que le seuil de PSB était inférieur à la limite de fatigue conventionnelle. La présence d'atomes interstitiels libres dans les aciers entraîne l'apparition d'une augmentation secondaire de la température dans la domain de la température stabilisée à 100-200 °C. Ce comportement semble être lié à l'interaction des dislocations coins avec des atomes interstitiels libres. De plus, on pense que le phénomène remarquable de durcissement-adoucissement-durcissement après l'élévation soudaine de la température jusqu'à plus de 300 °C est l'interaction de dislocations à vis multipliées et d'atomes interstitiels libresThis work attempts to a better understanding of the fatigue damage in ferrite-pearlite steels in the Very High Cycle Fatigue (VHCF) domain. The influences of two parameters, pearlite phase percentage and free interstitial atoms percentage in solid solution, are investigated to understand dissipative mechanisms under 20 kHz high frequency fatigue loading. In-situ infrared thermography is carried out to record the temperature changes, while fractography studies and microscope observations are conducted to investigate the dissipative mechanism on the surface of specimens.For body centered cubic (BCC) materials, under high stress amplitudes, a sudden increase of the temperature occurs without a crack initiation and fracture. The inevitable temperature increase up to hundreds of degrees at high stress amplitudes, is caused mainly by the screw dislocations mobility, which is the key to explaining the observed fatigue behavior and thermal response of BCC structure under high frequency loading. Therefore, PSBs on surface and micro-voids in matrix emerge massively, accompanying with this abrupt temperature increase. These phenomena are considered as transition of deformation mechanism from thermal regime to athermal regime. At low amplitudes, few PSBs or surface roughness are still observed on the specimen surface. Through the cycles of PSB appearance on armco-iron, it’s found that PSBs are inclined to appear before 1x10(7)cycles, and PSB threshold lies below the conventional fatigue limit. The increase of pearlite phase content weakens the temperature elevation, and strengthens the fatigue properties. The presence of free interstitial atoms in steels results in appearence of a secondary temperature increase in the stabilized temperature part (100-200 degree). This behavior seems to be related to the interaction of edge dislocations with free interstitial atoms. Moreover, the remarkable hardening-softening-hardening phenomenon after the sudden temperature elevation to above 300 degree is thought as the interaction of multiplicated screw dislocations and free interstitial atoms
40
Plennevaux, Cécile. "Etude des risques de corrosion et de rupture différée des aciers en présence d'H2S dans les conditions d'exploration de pétrole et de gaz à haute pression et haute température." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0101.
Анотація:
L'exploitation des champs de pétrole et de gaz sous haute pression (HP) et haute température (HT) a augmenté ces dernières années, nécessitant de réévaluer les risques de corrosion dans ces milieux de plus en plus sévères. Afin de contribuer à une meilleure évaluation des risques de rupture différée des aciers en présence d'H2S (SSC, Sulfide Stress Cracking) dans ces conditions, trois axes de recherche ont été suivis. Nous avons d'abord identifié un besoin d'amélioration de prédiction des conditions corrosives sous haute pression et haute température, et en particulier pour le calcul du pH in situ. Un modèle a été développé ; il prend en compte le comportement non-idéal des phases en équilibre, et permet un calcul plus précis du pH et de la fugacité des gaz acides à haute pression et haute température. Dans un deuxième temps, nous avons étudié l'effet de la pression partielle de CO2 (PCO2) sur les réactions de surface et sur les risques de SSC. Cette étude, réalisée à l'aide de mesures électrochimiques en l’absence d’un film de sulfure de fer, a permis de montrer que la présence de CO2 augmente sensiblement les cinétiques des réactions cathodiques à la surface de l'acier ainsi que le chargement en hydrogène, en particulier lorsque la pression partielle en H2S (PH2S) est faible. Enfin, des essais SSC ont été mis en œuvre dans des conditions fixes de pH et de PH2S, en faisant varier PCO2 entre zéro et 100 bar. L'objectif était de vérifier que la présence de CO2 sous forte pression augmentait bien les risques de fissuration, comme prévu par les résultats des essais électrochimiques. Les difficultés liées à la mise en œuvre d'essais en autoclave sous pression n'ont pas permis d'apporter une conclusion définitive. Néanmoins, ces travaux montrent qu'il peut exister un risque de sous-estimation de la sévérité des milieux dans les pratiques conventionnelles, lorsque PCO2 est significativement plus élevée que PH2S. Dans ces conditions spécifiques, les résultats de ce travail peuvent servir à améliorer les critères de choix de matériaux pour les milieux HP/HTThe production of high pressure (HP) and high temperature (HT) wells has considerably increased in the last decade. It is therefore needed to reassess the risks of corrosion in always more severe environments. This work was three fold to better assess the risk of Sulfide Stress Cracking (SSC) in these environments. Firstly, there was a need to improve prediction methods for the evaluation of HP/HT environments severity, especially the in situ pH calculation. A model was which taking into account the non-ideal behaviour of gas and liquid phases in equilibrium. The determination of the in situ pH and the acid gas fugacity at high pressure and high temperature is more accurate. In a second part of the work, the impact of CO2 partial pressure (PCO2) on surface reactions and hence on the risk of SSC was examined. Electrochemical and hydrogen permeation measurements in the absence of an iron sulphide film showed that CO2 induces an increase of both cathodic reactions kinetics and hydrogen charging in the steel, especially at low H2S partial pressure (PH2S). In the last part of this work, SSC tests were performed at constant pH and constant PH2S, with various PCO2 from 0 to 100 bar. The objective was to experimentally confirm that increasing PCO2 increases the SSC risk, as inferred from the electrochemical study. Unfortunately, experimental artefacts linked with autoclave test conditions did not lead to clear conclusions on this point. However, this work shows that conventional tools might lead to underestimate SSC risks at high PCO2 and low PH2S. In these specific conditions, the new results presented in this report may contribute to improve materials selection criteria for high pressure and high temperature conditions
41
Huang, Zhiyong. "Endommagement des aciers au C-Mn en fatigue oligocyclique et gigacyclique." Thesis, Paris 10, 2010. http://www.theses.fr/2010PA100088.
Анотація:
Dans les générateurs de vapeur des centrales nucléaires à eau pressurisée, les tuyauteries sont soumises à des chargements thermique et mécanique, qui sont variables et divisés en deux régimes différents : la fatigue oligocyclique et la fatigue gigacyclique. Les aciers au carbone – manganèse, type A42, A48 et Tu48 (normes françaises) sont souvent utilisés dans de telles applications. Les propriétés du matériau manifestent certains caractères spéciaux en mécanique et métallurgie comme le vieillissement dynamique conduisant à une augmentation de la valeur de la contrainte maximale et une diminution de la ductilité à la température 200 ℃. Le comportement en fatigue oligocyclique et gigacyclique sont étudiés à température ambiante et 200 ℃. Des essais de fatigue cumulée ont été mis en oeuvre pour étudier l’effet du cumul de dommage combinant des cycles de fatigue oligocyclique suivis de cycles en fatigue gigacyclique. Tous les résultats sont analysés en utilisant la mécanique de l’endommagement des milieux continus et l’analyse microfractographique. Les cycles d’hystérésis en fatigue oligocyclique sont dus à la déformation plastique de durcissement cinématique, ils peuvent être décrits par sous le modèle d’Armstrong – Frederick ; le durcissement isotrope est utile pour prédire l’évolution de l’amplitude de contrainte. Mais avec l’augmentation de la déformation plastique accumulée, le dommage ne peut être négligé. Le modèle de Chaboche d’endommagement par fatigue est utilisé pour décrire l’évolution des dommages oligocyclique et il est étendu au régime gigacyclique. Un modèle de fatigue cumulée des dommages a été développé à partir du modèle de Chaboche et appliqué à l’estimation des dommages de fatigue pour décrire le comportement de l’évolution de la contrainte en fonction du nombre de cycles. En fatigue oligocyclique à la température de 200 ℃, l’acier A48 est sensible au phénomène de vieillissement dynamique et il apparaît un durcissement secondaire, qui peut être prédit par la théorie des dislocations et est simulé dans la thése. L’analyse des surfaces de rupture est effectuée par fractographie au Microscope Electronique à Balayage pour les essais en oligocyclique, gigacyclique et cumul. En fatigue oligocylique, la fissure est initiée en surface. En fatigue gigacyclique, certaines fissures sont initiées sur des inclusions situées à l’intérieur d’éprouvettesIn steam generators of nuclear power plants, typical pipes components are subjected to thermal and mechanical loading which are variable and divided into two different regimes: low cycle fatigue and gigacycle fatigue. Carbon-manganese steels A42, A48 and Tu48 steels (French standards) are often used in such applications. The material properties manifest some special characters in mechanics and metallurgy such as Dynamic Strain Aging, increasing UTS values in 200℃ temperature domain. The LCF and VHCF behaviors are investigated respectively by test method at room temperature and 200℃. The cumulative fatigue tests are implemented through referencing the load as prior LCF following gigacycle fatigue from the steam generator pipes thermal loads in order to obtain the performance of material under accumulated fatigue damage. All the test results are analyzed by using plastic mechanics, continuums damage mechanics and microscopic analysis. Hysteresis loops are due to plastic deformation in LCF which is the effect of kinematic hardening and they can be described by Armstrong – Frederick form models; the isotropy hardening is used to predict the evolution of stress amplitude in LCF. But with rising of accumulated plastic deformation, the damage can not be neglected. The Chaboche fatigue damage model is applied to describe the damage evolution of LCF and extended to VHCF regime. The cumulative fatigue damage model is extended from Chaboche model and applies to the estimation cumulative fatigue damage. The constitutive relationship and isotropy rule are coupled with fatigue damage model that can describe the whole fatigue behavior. In 200℃ for LCF, A48 is sensitive to dynamic strain aging and its secondary hardening behavior is important which can be predicted by dislocation theory and is simulated in the paper. The fractographic analysis is performed by SEM for LCF, VHCF and cumulative fatigue tests. The LCF crack is initiated in surface. Some of cracks of VHCF are given birth from the inclusions located at interior of sample
42
El-Wazri, Abdelbaset M. "Processing and properties of high carbon microalloyed steels." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84240.
Анотація:
Five steels were used in the present work to investigate the dynamic, static and metadynamic recrystallization behavior of hypereutectoid steels of 1% carbon, alloyed with high silicon and microalloying levels of vanadium. Compression tests were performed using single and double hit schedules at temperatures between 875--1100ºC, strain rates of 0.01s-1 -1s-1, and inter-pass times of 0.1--500 seconds and 0.1--30 seconds for static recrystallization and metadynamic recrystallization, respectively. For dynamic recrystallization, it was found that an increase in carbon and vanadium content led to smaller grain sizes. Equations were generated that can be used to predict the critical strain for dynamic recrystallization. Of interest is the finding that there is an activation energy for deformation specifically associated with dynamic recrystallization (i.e. peak strain). This activation energy associated with the peak strain is lower than that associated with the steady state stress. This is contrary to Sellar's original observation that the peak strain is a function of the activation energy for deformation according to the Zener-Hollomon relationship. The static recrystallization kinetics were measured, and the appearance of 'plateau' regions where softening is arrested for a period of time was used to quantify the kinetics of strain-induced precipitation and generate the precipitation temperature time diagrams for the three steels. Despite the wide range of V levels, the steels exhibited very similar precipitation kinetics at all temperatures tested, being particularly close below 950ºC. A kinetic equation for static recrystallization is proposed which takes the V and Si concentrations into account. The metadynamic recrystallization results show that there is a transition strain region in which both static and metadynamic recrystallization take place during the inter-pass time. The results also revealed that V and Si have a strong solute dra
43
Lodwig, Geraint Wyn. "Hot dip coating of high strength low carbon steels." Thesis, Swansea University, 2004. https://cronfa.swan.ac.uk/Record/cronfa42742.
Анотація:
In response to increasing demand for high strength automotive steels, the development of galvanised dual phase steels has become more significant in recent years. At present, a requirement for galvanised high strength steels with tensile strengths in excess of 600 MPa exists within the automotive industry. The present programme focuses on seven C-Mn based steels, each steel varying in key additions such as silicon, chromium, vanadium, molybdenum and niobium. A composition range wt% of C (0.07-0.2), Mn (1.3-1.5), Si (0.05-1.3), Cr (0.05-0.45), V (up to 0.01), Mo (up to 0.01) and Nb (0.001-0.01) was studied. In order to attain these wide-ranging steel chemistries, both commercially produced and laboratory cast steels were used for this project. All steels had the required chemistry for dual phase steel production, but only if a suitable annealing cycle was used. As a result, all steels were subjected to a range of annealing cycles on a laboratory-annealing simulator, based on current continuous annealing/galvanising line schedules utilised by the Corus Group. Steels identified as dual phase steels from annealing experiments by microstructural and mechanical property analysis were subjected to laboratory galvanising. The zinc coating applied to these steels has been studied to evaluate the quality of the galvanised steel. This investigation, which has utilised a galvanising simulator, has demonstrated that during standard galvanising practices, problems known as dewetting affected the coating quality. Unfortunately, this issue was most prevalent with the steels displaying the most suitable metallurgical properties. Nevertheless, the wetting performance could be vastly improved by varying processing conditions such as annealing furnace dew point and strip entry temperature.
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Lencina, Rodrigo. "Optimization of high carbon austenitic manganese steels for comminution processes." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3424542.
Анотація:
Austenitic manganese steels are widely used in mineral comminution processes due to their good wear resistance and high toughness. The classical chemical composition for austenitic manganese steel in these applications is about 12%Mn and 1.2%C, steel first produced by R. Hadfield more than a century ago. Ever since, many efforts to improve its mechanical properties and wear resistance have been made, mostly driven by the continuous demand of the mining industry for bigger crushing equipment and lower production costs.
In this work, two types of austenitic manganese steels containing a relative high content of carbon are investigated. The high carbon content provided the steels good wear resistance, but compromises their mechanical properties. An important deleterious effect observed due to high carbon content was embrittlement due to the precipitation of carbides at grain boundary.
Another important feature of the steels under study was their difference in manganese content, which played an important role in stabilizing carbon in the austenitic matrix. Furthermore, both steels contained titanium, which contributed to increase wear resistance through the formation of a hard phase of stable carbides.
Heat treatments were performed, aimed to solubilize precipitated carbides and to improve quenching conditions, in order to avoid reprecipitation of these carbides, especially in thick castings. The results presented showed a correct selection of the temperature for austenitization and, additionally, a characterization of the kinetics of the re-precipitation phenomenon.
After the improvements of the microstructure, the steels were tested in pilot scale crushers to assess their wear properties. Additionally, field tests were performed as well in industrial applications: in a cone crusher, a horizontal shaft impactor and a hammermill.
The results of the metallurgical and tribological studies demonstrated the need for improvements in the chemical composition of the steels. For this reason, different elements, such as Nb, Al, Ni, Mo, were added to the composition of the steels. Finally, a cost estimation of the industrial production of these new steels was performed, in order to assess their economic feasibility.
The results showed that the phenomenon of carbide re-precipitation is the main reason for embrittlement. Manganese content was the most important variable to stabilize the microstructure. The addition of Ni to this steel resulted in an improvement of mechanical properties, while maintaining the good wear resistance.
Two appendixes are included with original research work that was secondary to the scope of the thesis project. The first, presents a mathematical model that simulates the granulometric curve of the product from a crusher, but taking in consideration the wear in the liners of the machine. The other, presents an ultrasound treatment, which had comminution effects in different types of mineral particles. Ultrasound was tested as well in a leaching process to investigate their kinetic enhancement effects.Gli acciai austenitici al manganese sono largamente utilizzati nell’industria mineraria poiché hanno un’elevata resistenza all’abrasione e un altissima tenacità. La composizione chimica più diffusa nell’attività mineraria è di circa 1.2% C e 12% Mn, composizione che è stata prodotta per prima volta da R. Hadfield più di un secolo fa. Da questo momento, molte ricerche sono state eseguite per migliorare le proprietà meccaniche e la resistenza all’usura di questi acciai. Soprattutto perché la industria mineraria attuale richiede costi di produzione più bassi e frantoi con più grande capacità. In questo studio, sono presentati due acciai austenitici al manganese, i cui contenuti di carbonio sono considerevolmente alti. Questo contenuto di carbonio fornisce agli acciai buona resistenza all’ usura, ma diminuisce le proprietà meccaniche. Un effetto non desiderato del alto contenuto di carbonio è il infragilimento dovuto alla re-precipitazione di carburi a bordo grano. Un'altra caratteristica importante degli acciai studiati è il loro contenuto di manganese, che ha avuto un ruolo preponderante nella stabilizzazione del carbonio nella matrice austenitica. Anche, entrambi acciai contenevano del titanio, elemento che ha contribuito a incrementare la resistenza all’usura tramite la formazione di carburi duri e stabili. Sono stati eseguiti dei trattamenti termici allo scopo di solubilizzare delle fasi precipitate e anche a migliorare la condicione di tempra in modo di evitare la re-precipitazione di questi carburi, specialmente nei getti di grosso spessore. I resultati ottenuti forniscono una temperatura ottimale per la austenitizazione degli acciai e anche, caratterizzano la cinetica di re-precipitazione dei carburi a bordo grano. Dopo le procedure di miglioramento della microstruttura, i due acciai sono stati testati a scala pilota utilizzando dei piccoli frantoi. Anche, sono stati eseguiti test sul terreno, in diverse machine a livello industriale: frantoio a cono, mulino a asse orizzontale e mulino a martelli. I resultati delle studi metallurgici e tribologici hanno dimostrato la necessita di miglioramenti nella composizione chimica degli acciai. Quindi, diversi elementi sono stati aggiunti agli acciai (Nb, Al, Ni, Mo). Alla fine, è stata eseguita una stimazione dei costi di produzione per gli nuovi acciai, allo scopo di valutare la loro fattibilità economica. Pertanto, è stato dimostrato che il fenomeno di re-precipitazione è la causa più importante del infragilimento. Il contenuto di manganese è stato la varabile più importante per stabilizzare la microstruttura. La aggiunta di nichel a questo acciaio a permesso la migliora delle proprietà meccaniche, e allo stesso tempo di mantenere la resistenza all’usura. Se inseriscono due appendici contenenti lavori di ricerca che non apparteneva allo scopo principale della tesi. La prima appendice tratta un modello matematico che simula la curva granulometrica del prodotto appartenete a un frantoio. Il modello prende in considerazione la perdita di qualità dovuta alla usura dei rivestimenti. L’altra appendice parla di un trattamento di ultrasuono eseguito allo scopo di macinare delle diverse particelle di rocce. Anche, questo trattamento è stato impiegato in uno sperimento idrometallurgico allo scopo di verificare l’incremento della cinetica di lisciviazione.
45
LIMA, LIANA M. F. G. de. "Estudo da evolução da textura, da microtextura e da mesotextura de recristalização, após baixos graus de deformação a frio, em dois aços ferríticos com baixo teor de carbono." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11269.
Анотація:
Made available in DSpace on 2014-10-09T12:50:07Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:02:06Z (GMT). No. of bitstreams: 1 10457.pdf: 13419642 bytes, checksum: 823b4f1fc4fdfe5858d116b42196a9c2 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
46
Bradley, Rusudan. "The effect of workpiece compostion of free-cutting steels on machinability using coated and uncoated high speed tools." Thesis, Liverpool John Moores University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388522.
47
Husain, Khaled Salman Adwan. "Microstructure and properties of low-carbon steels processed by high pressure torsion." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386907/.
Анотація:
In this study, low-carbon steel (0.1 wt.% C) in ferritic-pearlitic (FP) and ferritic-martensitic (FM) initial states were processed by high pressure torsion (HPT) up to 10 turns under a pressure of 6 GPa at room temperature (RT). The HPT-processed FM samples were tempered at 150oC to 550oC. The microhardness monotonically increased with the number of turns up to 10 turns. After 10 turns, the microhardness had increased to 3 times that of the initial state for both the FP and FM samples. The microhardness of the individual phases, ferrite and martensite, in the FM processed samples increased with strain. The nanoindentation measurement of the ferrite in the FP processed samples revealed that the ferrite nanohardness increased with the number of turns up to 10 turns. The microhardness was maintained when the FM sample processed up to 4 turns and tempered at 450oC while the microhardness slightly increased when tempering at 350oC. Similarly, the ferrite in the FM sample processed up to 4 turns and tempered at 350oC had a nanohardness value higher than that of the sample tempered at 250oC: this can be attributed to the limited formation of cementite particles in the ferrite matrix. Optical and scanning electron microscopy (SEM) revealed that cementite fragmentation in the FP samples started after 4 turns of HPT processing and increased with the number of turns, or strain. SEM investigation revealed the formation of cementite particles when the FM sample processed up to 4 turns and tempered at 450oC: these cementite particles coarsened when tempering at 550oC. The transmission electron microscopy (TEM) investigation of the microstructure in the FM processed samples revealed that the microstructure was characterised by high internal stresses and dislocation density. The dislocation cells evolved during the HPT processing up to 10 turns and the fraction of high angle grain boundaries increased with the number of turns. X-ray diffraction (XRD) analysis revealed that no appreciable lattice parameter (a) expansion occurs during the HPT processing of the ferrite of the FP samples. The lattice parameter of the ferrite of the FM processed samples increased with the number of turns, or strain. The lattice parameter of the ferrite of the FM sample processed up to 4 turns and tempered at 450oC was equal to that of pure α-iron which suggests that the cementite particles formed at the expense of the decomposition of the supersaturated Fe-C solid solution in ferrite. It is well documented in the literature that the strength or hardness significantly increases with the number of turns during HPT processing. However, so far no attempt has been made to predict the strength of low-carbon steels after HPT processing. In this study, the X-ray line profile analysis (XLPA) using the multiple whole profile fit (MWP-fit) was used, as an alternative tool to TEM, to determine the dislocation density in the HPT-processed samples. A model that incorporates both the dislocation and grain boundary strengthening was proposed to predict the strength of the HPT-processed samples. In this model, other strengthening contributions such as solid solution and Orowan strengthening due to different structures such as pearlite, martensite, and carbide particles in the ferrite matrix were taken into account. The strength/hardness model proposed in this study was applied to predict the strength/hardness of six low-carbon steel (0.1 wt.% C) samples in the ferritic-pearlitic or ferritic-martensitic initial states processed by HPT up to 1, 4, and 10 turns. Furthermore, the strength/hardness model was also applied to predict the strength of FM samples processed by HPT and tempered at different temperatures. The strength/hardness model proposed in the current study can be used to predict the strength of all the investigated samples to a good accuracy with an average error of ±8%.
48
Chamisa, Alfonce. "Development of ultra high strength steels for reduced carbon emissions in automotive vehicles." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/6274/.
Анотація:
Automotive steels with enhanced strength and ductility beyond the current bounds can be engineered through microstructural strategies that take into account the benefits brought about by nanoprecipitates formed during the transformation from austenite to ferrite. Three multiphase steel compositions were initially studied. A patented Ti-Al-Mo steel composition was selected as the baseline for comparison with the other two steels. It is claimed that this steel has exceptional mechanical properties. The Ti and V microalloyed steels were selected to check whether interphase precipitates (IP), which can yield a high degree of precipitation strengthening, could be produced. Results showed that Ti-Al-Mo had superior microstructure and properties as compared to the other two. The microstructure was composed of ferrite, martensite, bainite and retained austenite. Unlike the other two steels, IP was also observed and the UTS of 780MPa and uniform elongation of 21% previously reported by other authors were also confirmed. The V microalloyed steel composition was selected for the next part of the project since it would be commercially viable to produce for Tata Steel. The time/temperature/transformation behaviours of the V microalloyed steel were extensively studied. The microstructures developed were analysed and high precipitate number densities averaging 394 particles/m2 were recorded in the sample transformed at 700oC for 1200s. A high uniform elongation of 30.8% and the highest UTS of 627MPa were also reported on the same sample. The UTS value was attributed to the high precipitate number density which made an overall contribution to the yield strength of 270MPa. However, further studies need to be carried out, since the properties were not optimised and were inferior to some of the steels in current use for automotive applications. Questions were asked as to why IP was not observed. The low austenising temperature of 950oC was cited as the possible reason. Thermodynamic calculations using Thermo-Cal software had predicted that the optimum should have been 1050oC. As a result, 950oC was believed to be inadequate to effectively dissolve the carbides present to allow effective formation of interphase precipitates during the temperature hold in the α + γ temperature region. The high N content was cited as another possible reason, but this was not conclusive and shown in itself not to be true by work in the next stage of the project. It has since been established that Mo retards precipitate growth in both Nb and Ti alloyed steels. However, nothing has been reported on the effects of Mo on V microalloyed steels. As a result, the next stage of the project studied the effects of Mo on V microalloyed steels. Predominantly ferritic steels with Nb-V-Mo microalloying additions were produced and coiled at different temperatures. Samples microalloyed with Ti-Mo, Ti, V-Mo, V, Nb-Mo and Nb were also produced for comparison purposes. IP was observed in most of the Nb-V-Mo steels. IP with average interparticle distances of 8 ± 2nm and row spacing of 22 ± 3nm were observed in sample 10-630Nb+VMo. High YS of 925MPa, UTS of 1023MPa and total elongation of 16.8% were recorded for this sample. The exceptional mechanical properties were attributed to high number densities of fine IP averaging 1766 particles/m2. 82% of the precipitates had average sizes below 7nm and these made a contribution to YS of approximately 546MPa. It was then concluded that Mo additions were likely to have influenced the formation of fine precipitates that strengthened the ferritic steels. Hence Mo is likely to influence the high nucleation rate and slow precipitate growth in the same way that it influences Ti and Nb microalloyed steels. Since one of the steels studied at this stage had high N additions, it was also confirmed that the precipitate number densities in the previous V microalloyed steels batch had nothing to do with the N content; instead, it all had to do with the low austenising temperature which failed to put the carbides into solution.
49
Erkami, Ali Akbar. "The studies of high strain deformation in carbon steels containing differing amounts of pearlite." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303427.
50
Manoharan, Mohan. "Combined mode I - mode III plane strain fracture toughness of two high carbon steels /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970651702.