Dissertations / Theses: 'Steel alloying'

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Marsden, Charles F. "Laser surface alloying of stainless steel." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47176.

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Gregg, John Martin. "Ferrite nucleation on non-metallic inclusions in steel." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/221878.

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Chen, Jhewn-Kuang. "Effects of alloying elements upon austenite decomposition in high strength low alloy steels." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-10102009-020227/.

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Nounezi, Thomas. "Light Weight and High Strength Materials Made of Recycled Steel and Aluminum." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20523.

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Recycling has proven not only to address today’s economical, environmental and social issues, but also to be imperative for the sustainability of human technology. The current thesis has investigated the feasibility of a new philosophy for Recycling (Alloying-Recycling) using steel 1020 and aluminum 6061T6. The study was limited to the metallurgical aspects only and has highlighted the potential of recycled alloys made of recycled aluminum and steel to exhibit substantially increased wear resistance and strength-to-weight ratio as compared to initial primary materials. Three alloy-mixtures are considered: TN3 (5wt% 1020 +95wt% 6061T6); TN5 (0.7wt% 1020 + 99.3wt% 6061T6); and TN4 (10wt% 6061T6 + 90wt% 1020). A Tucker induction power supply system (3kW; 135-400 kHz) is used to melt the alloy mixtures for casting in graphite crucibles. Heat treatment of the cast samples is done using a radiation box furnace. Microscopy, Vickers hardness and pin-on-disc abrasive wear tests are performed. Casting destroyed the initial microstructures of the alloys leading to a hardness reduction in the as-cast and solution heat-treated aluminum rich samples to 60 Hv from 140 Hv. Ageing slightly increased the hardness of the cast samples and provided a wear resistance two times higher than that of the initial 6061T6 material. On the steel rich side, the hardness of the as-cast TN4 was 480 Hv, which is more than twice as high as the initial hardness of steel 1020 of 202 Hv; this hints to strong internal and residual stress, probably martensite formation during fast cooling following casting. Solution heat treatment lowered the hardness to the original value of steel 1020, but provided about ten (10) times higher wear resistance; this suggests higher ductility and toughness of normalised TN4 as compared to 1020. In addition, TN4 exhibits about 25% weight reduction as compared to 1020. The actual recycling process and the effect of non-metallic impurities shall be investigated in future works. Also, the casting and heat treatment processes need to be improved.

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Dong, Yangchun. "Towards multi-functional stainless steel surface : plasma surface alloying with N, Ag and Cu." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1455/.

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Hospital-acquired infections, a large proportion of which are derived from contact transmission, represent a massive global challenge. It has been proved that surface modification of biomaterials with Ag or Cu has evolved as a potentially effective method for preventing bacterial proliferation on the devices surfaces. However, thin antimicrobial coatings on materials such as austenitic stainless steels can be easily worn and removed in relative motion with other surfaces. The purpose of this study is to develop multi-functional stainless steel surfaces which combine greatly improved wear resistance, at least maintain corrosion resistance and provide long-lasting, high efficacy, antimicrobial effects. In this thesis a series of surface engineering technologies, including active screen co-alloying, active screen plasma duplex alloying and double glow plus active screen duplex plasma alloying, were developed for surface alloying stainless steel with Ag or Cu and N; the phase constitution, microstructure, composition, and surface roughness of the alloyed surfaces were fully characterized, and the surface hardness, wear resistance, bonding strength, antimicrobial efficiency and corrosion behaviour of the treated surfaces were evaluated. In addition, further inspection of the wear mechanisms and corrosion mechanisms were conducted on post-exposure surfaces. It was found that the adhesive wear mechanism of austenite can be reduced by this alloying combination and the wear resistance was improved by up to 1000 times, and the Ag/Cu alloyed surface was bactericidal and growth-inhibitive for many pathogens including E. coli NCTC 10418 and S. epidermidis NCTC 11047 effectively up to 99%/6h. The mechanism of bactericidal efficiency of Ag/Cu is found dependent on the structure of the bacterial membrane and a higher efficiency of antibacterial agents is found associated with the higher elemental concentration of copper and silver. With regard to corrosion, it is affected largely by the configuration of surface structure and several corrosion mechanisms were evolved. One principal conclusion was that it is feasible to generate long lasting antimicrobial stainless steel surface to fulfil growing demands from industry for practically robust multifunctional medical device surfaces.

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van, Niekerk Cornelis Janse. "In-situ alloying of AISI 410L martensitic stainless steel with nitrogen during laser cladding." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61341.

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The feasibility of in-situ alloying of AISI 410L martensitic stainless steel with nitrogen during Nd-YAG laser cladding was investigated with the aim of achieving a nitrogen content of at least 0.08 wt% and fully martensitic microstructures in the final clad deposit. Two in-situ nitrogen alloying techniques were studied. In the first set of experiments, the absorption of nitrogen from nitrogen-rich gas atmospheres was studied. Laser cladding with commercially available AISI 410L powder was performed using nitrogen-rich shielding and carrier gas. A marginal increase in deposit nitrogen content was observed, with the clad deposit displaying low hardness and mostly ferritic microstructures. Poor nitrogen absorption from nitrogen-containing atmospheres during Nd-YAG laser cladding is generally attributed to the short thermal cycle and to suppression of plasma formation above the weld pool. In the remaining experiments, Si3N4 powder was investigated as an alternative source for nitrogen during cladding. The addition of Si3N4 to the AISI 410L powder feed resulted in clad microstructures consisted of columnar -ferrite grains with martensite on the grain boundaries, higher hardness and an increase in deposit nitrogen content (to a maximum of 0.064 wt% nitrogen). Higher nitrogen contents in the clad deposit, however, significantly increased the volume percentage porosity in the clad layer. This prompted an investigation into the feasibility of raising the nitrogen solubility of the alloy through additions of manganese and nickel to the powder feed. Thermodynamic modelling revealed that the addition of manganese to AISI 410L powder increases the nitrogen solubility limit due to its negative interaction parameter with nitrogen. The addition of up to 3.5 wt% manganese to AISI 410L powder containing Si3N4 significantly increased the nitrogen solubility in the deposit. A martensitic microstructure with 0.12 wt% nitrogen and a peak hardness of 410 HV was achieved without any adverse increase in porosity in the clad layer. The clad nitrogen content easily exceeded the minimum requirement of 0.08 wt%. High nickel concentrations in AISI 410L stainless steel expand the austenite phase field at the expense of -ferrite and alter the solidification mode from ferritic to austenitic-ferritic. The addition of up to 5.5 wt% nickel, or combinations of nickel and manganese, to the nitrogen-alloyed AISI 410L powder feed raised the deposit nitrogen content, but not to the same extent as those deposits alloyed with manganese only. Since more austenite is present on cooling in nickel-alloyed AISI 410L deposits, less nitrogen is rejected to the liquid phase on solidification, resulting in higher nitrogen contents and less porosity in the room temperature microstructures. The amount of dilution during single-track laser cladding is mainly influenced by the specific energy per unit mass delivered by the laser beam. The clad height is strongly influenced by the powder deposition rate, whereas the bead width is influenced by the wettability of the deposits during laser cladding. During multi-track cladding, the observed percentage porosity is a function of the aspect ratio of the individual beads making up the clad layer, the deposition rate and the clad height. High deposition rates result in thicker layers, increasing the distance that N2 gas bubbles have to travel to escape to the atmosphere, while a high aspect ratio favours interbead porosity. The results suggest that in-situ nitrogen alloying during laser cladding should preferably be performed at low deposition rates to ensure higher clad nitrogen contents and hardness, lower clad heights, less dilution and less porosity. Dissertation (MEng)--University of Pretoria, 2016. Materials Science and Metallurgical Engineering MEng Unrestricted

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Voyevodin, V. N., A. N. Velikodniy, M. A. Tikhonovskiy, A. S. Kalchenko, S. V. Starostenko, and N. I. Danilenko. "Effect of Alloying Oxides Y2O3 and ZrO2 on the Microstructure of Austenitic Steel 18Cr10NiTi." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42782.

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Nanomaterials are materials of new generation with unique characteristics which are not characteristic for other materials. Nanofilms, nanoprocessors, nanorobots – the more well known technologies, but demands of modern industry, electronic industry, power industry dictate the development of nanomaterials in higher scales. The use of nanomaterials is very promising direction in nuclear power. Conditions of operation of structural materials in nuclear reactors, namely, high temperature (higher 300°C for thermal reactors and higher 600°C for fast reactors) which together with high density of neutrons (~1021-1022 neutrons/cm-2) cause the degradation of initial physical-chemical characteristics and the significant dimension changes. These factors influence considerably on safe and long-term operation period of reactor.

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Heikkilä, Irma. "The Positive Effect of Nitrogen Alloying of Tool Steels Used in Sheet Metal Forming." Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-198747.

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Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes. A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced. The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation. The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives. The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides. The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.

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Viano, David Michael. "The influence of alloying additions on the microstructure and mechanical properties in high current GTA welding of structural steel /." Title page, abstract and contents only, 1998. http://web4.library.adelaide.edu.au/theses/09ENS/09ensv617.pdf.

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Solheim, Ulrika, Anna Willman, and Marja Wedberg. "An evaluation of alloying elements in shredded steel scrap : Economic and environmental aspects of the recycling process for the steel scrap category E40." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209825.

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Bergman, Ola. "Studies of oxide reduction and nitrogen uptake in sintering of chromium-alloyed steel powder." Licentiate thesis, KTH, Materials Science and Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9555.

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The powder metallurgy (PM) process route is very competitive for mass production of structural steel components with complex shape, due to efficient material utilisation, low energy consumption, and short overall production time. The most commonly used alloying elements are the processing friendly metals Cu, Ni and Mo. However, the prices for these metals are today high and volatile, which threatens to make the PM process less competitive compared to conventional metal forming processes. Consequently, there is a strong desire in the PM industry to increase the use of less costly alloying elements. Cr is an attractive alternative since it, besides low cost, provides high hardenability and also recyclable components. The drawback is that Cr has high affinity for oxygen, which makes oxidation and oxide reduction in PM processing of Cr-alloyed materials a challenging issue. Furthermore, the interaction between nitrogen and Cr-alloyed powder during processing is important to consider, since Cr also has high nitrogen affinity and is prone to form nitrides.The aim of the research work presented in this thesis was to study oxide reduction and nitrogen uptake in sintering of Cr-alloyed steel powder. Water-atomized powder grades pre-alloyed with 1.5-3% Cr were used as test materials. Sintering experiments were performed in N2/H2 (90/10) atmospheres with test bars pressed to density 7.0-7.2 g/cm3. The oxygen content of the sintering atmosphere was varied and different sintering temperatures and cooling rates were applied. The experimental study has been complemented with thermodynamic calculations using the software Thermo-Calc.The oxygen partial pressure should be below 4 x 10-18 atm in order to have reducing conditions during sintering at 1120°C of steel powder pre-alloyed with 3% Cr. With graphite added to the powder, conditions are reducing at higher oxygen partial pressures (up to 10-16 atm) due to favourable conditions locally in the material. Sintering at 1120°C for 30 minutes leads to incomplete reduction of Cr-oxides in the Cr-alloyed PM grades, but remaining oxides are not detrimental for mechanical properties of the PM components. Increased sintering temperature is beneficial for the oxide reduction kinetics and practically all oxides are reduced after sintering for 30 minutes above 1200°C. Nitrogen uptake by Cr-alloyed steel powder from N2-based sintering atmospheres is strongly dependent on the cooling rate applied after sintering. No nitrides appear in the sintered material and mechanical properties are not affected when normal cooling rates (0.5-1°C/s) are applied. Very low cooling rates (such as 0.05°C/s) may lead to grain boundary precipitation of Cr-nitrides in the sintered material.

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Aiso, Toshiharu. "Workpiece steels protecting cutting tools from wear : A study of the effects of alloying elements on material transfer and coating damage mechanisms." Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-306190.

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The vision of this thesis is to improve the machinability of workpiece steels. Workpiece material frequently transfers to the cutting tools during machining, and the transfer layers then forming on the tools may give both good and bad effects on machining performance and tool life. The objective of this work is to understand the effects of alloying element additions to workpiece steels on material transfer and the roles of the formed transfer layers on friction characteristics and wear of tools. To isolate and study the influence of the individual alloying elements, model steels are specifically designed. These steels include one reference with C as the only alloying element and others alloyed also with single additions or combined additions of 1 mass% Si, Mn, Cr and Al. The experiments are performed using both a sliding test, simulating the material transfer in milling, and a turning test. In a sliding contact, the mode of transfer is strongly dependent on the normal load and sliding speed. Material transfer initiates extremely fast, in less than 0.025 s, and characteristic transfer layers develop during the first few seconds. The different steel compositions result in the formation of different types of oxides in the transfer layers. At the workpiece/tool interface where the conditions involve high temperature, high pressure and low oxygen supply, easily oxidized alloying elements in the steel are preferentially transferred, enriched and form a stable oxide on the tool surface. The degree of enrichment of the alloying elements in the oxides is strongly related to their tendencies to become oxidized. The difference in melting temperature of the oxides, and thus the tendency to soften during sliding, explains the difference in the resulting friction coefficient. The widest differences in friction coefficients are found between the Si and Al additions. A Si containing oxide shows the lowest friction and an Al containing oxide the highest. The damage mechanism of coated tools is chiefly influenced by the form and shear strength of the transferred material. Absence of transfer layer or non-continuous transferred material leads to continuous wear of the coating. Contrastingly, continuous transfer layers protect it from wear. However, transfer layers with very high shear strength result in high friction heat and a large amount of steel transfer. This leads to rapid coating cracking or adhesive wear.

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Chychko, Andrei. "Energy and environmental optimization of some aspects of EAF practice with novel process solutions." Doctoral thesis, KTH, Materialens processvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24486.

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The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming. QC 20100914

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Husák, Roman. "Mechanické legování a zhutňování kovových kompozitních prášků." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231362.

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Master´s thesis is focus on the proces of mechanical alloying. It is the proces of modifying a hetegeneous mixture of powder materials into a homogeneous composite powder. Experiments are focus on three types of composite materials. A magnetic soft alloy Permalloy, ODS steel based on commercially available powder steel 434 LHC and low-activation high-chrome ODS steel 14Cr-2W. On composite powders are made a series of mechanical tests and chemicel analysis. Based on this tests and analysis it was possible to confirm the milling time needed to create fully homogeneous composite powder. Next step is compaction of composite powder into compact volume and another mechanical tests ana analysis of microstructure. In these analyzes to determine whether i tis necessary to use protective atmosphere during mechanical alloying. All three type of materials succesfull prepared by mechanical alloying. It was found that for created of a fully homogeneous composite powder is necessary to perform mechanical alloying for 24 hours. When processing of corrosion resistant materials, i tis possible to perform mechanical alloying in an air atmosphere. During mechanical alloying materials which are subject to oxidation, i tis necessary to use protective atmosphere.

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Giard, Baptiste, and Sofia Karlsson. "Machine learning for the prediction of duplex stainless steel mechanical properties : Hardness evolution under low temperature aging." Thesis, KTH, Materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298415.

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Duplex stainless steels, DSS are stainless steels that consist of the two phases austenite and ferrite. The DSS have superb properties and are widely used in industries such as nuclear power and in pressure vessels, pipes and in pipelines. The use of DSS are limited due to embrittlement which occurs at temperatures from 250 to 550 oC. This imposes a general limited service temperature of 250 oC. The mechanism mainly responsible for the embrittlement is a phase separation occurring in the ferrite phase. Furthermore, there is a direct link between the phase separation and the mechanical properties: the ferrite hardness increases whereas the toughness decreases under low temperature aging. In this thesis, the low-temperature embrittlement of duplex stainless steels was studied through machine learning modelling and experimental hardness- and microscopy measurements. The resulting model describes the data with an accuracy, R-squared = 0.94. In combination with the experimental results, nickel was identified as an important parameter for the hardness evolution. This work aims to provide a fundamental study for understanding the importance of alloying elements on the phase separation in DSS, and provides a new methodology via a combination of machine learning and key experiments for the material design. Duplexa rostfria stål är rostfria stål som består av de båda faserna ferrit och austenit. De har extraordinära egenskaper och används brett inom industrin, t ex. i kärnkraftverk och i tryckkärl och pipelines. Användningen av duplexa rostfria stål är begränsad p.g.a. försprödning som uppstår i legeringarna vid temperaturer mellan 250-550 oC, vilket medför att den tillåtna temperaturen vid användning begränsas till under 250 oC. Den främsta orsaken till försprödningen är en fasseparation i den ferrita fasen under åldring vid låg temperatur. Vidare leder fasseparationen till mekaniska förändringar i ferritfasen: hårdheten ökar medan segheten minskar. I den här rapporten undersöks försprödningen av duplexa rostfria stål vid åldring med hjälp av datormodellering med maskininlärning samt av experimentella hårdhets- och mikroskopiska mätningar. Modellen hade en noggrannhet (determinationsko- efficienten, R2) på 0.94. Resultatet från modellen visade tillsammans med de experimentella resultaten att nickel är ett legeringsämne som har stor betydelse för hårdhetsökningen. Detta arbete syftar till att utgöra en grundläggande studie för att förstå påverkan från olika legeringsämnen på fasseparationer i DSS, och bidrar med en ny metodik för materialdesign som kombinerar maskininlärning och utvaldaexperiment. EIT RawMaterial Project ENDUREIT

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Nilsson, Hultén Leo. "Nitrogen Without Oxygen : The effect of ferroalloys added after vacuum treatment on cleanliness of nitrogen-alloyed tool steel." Thesis, KTH, Materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298093.

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Nitrogen-alloyed tool steel is made at Uddeholms AB by adding high-nitrogen ferroalloy after vacuum degassing where introduced impurities are hard to remove. In this thesis two types of high-nitrogen ferrochromium are compared, a solid version and a powder cored wire. They are examined in crossection and 16 samples from four charges are examined with Pulse Distribution Analysis as well as systematic microscopy of polished cross sections. The PDA results missed smaller spinel inclusions shown in previous research to be detrimental. The wire form shows promise but more charges need to be evaluated before a conclusion is drawn. Kvävelegerat verktygsstål tillverkas hos Uddeholms AB genom tillsats av kväverika ferrolegeringar efter vakumavgasning, och orenheter som introduceras i detta steg är svåra att avskilja. I den har uppsatsen jämförs två typer av kväverikt ferrokrom varav en i form av stycken och en i form av tråd med pulverkärna. De undersöks i tvärsnitt och totalt 16 prov från fyra charger undersöks med PDA (pulsfördelningsanalys) och systematisk mikroskopering i tvärsnitt. Resultaten från PDA missade mindre inneslutningar av spinell vilka tidigare har visat sig problematiska. Trådformen verkar lovande men fler charger behöver undersökas för att kunna dra en definitiv slutsats.

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Kisko, A. (Anna). "Microstructure and properties of reversion treated low-Ni high-Mn austenitic stainless steels." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526212159.

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Abstract In this thesis, the influence of reversion and recrystallization annealing on microstructure and mechanical properties was studied in metastable austenitic low-Ni high-Mn stainless steels, some alloyed with up to 0.45 wt.% Nb. Further, the effect of the various microstructures created by reversion and recrystallization on strain-induced martensite transformation in tensile testing was investigated. The aim was to achieve excellent combinations of strength and ductility in the steels and to improve understanding of the behaviour of ultrafine-grained austenitic stainless steels during deformation. All the steels were cold-rolled up to 60% thickness reduction producing up to 60% strain-induced α’-martensite in the austenitic structure. Annealing was carried out using a Gleeble thermomechanical simulator between 450–1100 °C for durations of 0.1–1000 s. The resultant microstructures were examined using different research equipment and methods. Regardless of the amount of Nb alloying, shear- and diffusion-controlled reversion could be completed by annealing at 700 °C, although at this temperature no recrystallization of the untransformed cold-rolled austenite occurred. At 800 °C, however, the cold-rolled austenite recrystallized, producing a non-uniform grain structure comprising ultrafine-grained areas formed via reversion and coarser ones formed by recrystallization of the retained austenite. At 900 °C, a uniform fine austenite grain size of about 2 μm was obtained. At higher annealing temperatures of 1000–1100 °C, normal grain growth of fine grains took place during prolonged annealing in steel with no Nb. However, grain growth was effectively retarded by alloying with 0.28 wt.% Nb. The non-uniform structures consisting of reverted and retained austenite exhibited excellent combinations of yield strength and uniform elongation. The results also showed that tensile strain-induced martensite nucleation sites and α’-martensite formation vary in a complex way depending on grain size Tiivistelmä Väitöstyössä tutkittiin reversiohehkutuksen vaikutusta metastabiilin 1% nikkeliä ja 9% mangaania sisältävien austeniittisten ruostumattomien terästen mikrorakenteeseen ja mekaanisiin ominaisuuksiin sekä austeniitin raekoon ja mikrorakenteen vaikutusta muokkausmartensiitin syntyyn vetokokeessa. Koeteräksistä osa oli lisäksi niobiseostettuja. Tavoitteena oli nostaa teräksien lujuutta ja ymmärtää ultrahienorakeisen austeniittisten ruostumattomien terästen käyttäytymistä muokkauksessa. Teräkset kylmämuokattiin 60% valssausreduktiolla, jolloin austeniittiseen rakenteeseen muodostui muokkausmartensiittia enimmillään 60%. Reversiohehkutukset tehtiin Gleeble termomekaanisella simulaattorilla lämpötiloissa 450–1100 °C ja 0.1–1000 s pitoajoilla. Saatuja mikrorakenteita tutkittiin eri tutkimuslaitteistoilla ja -menetelmillä. 700 °C hehkutuksessa leikkautumalla ja diffuusion välityksellä tapahtuva reversio oli nopea myös niobi-seostetuilla teräksillä, mutta rekristallisaatiota ei tapahtunut. 800 °C hehkutuksessa muokkauksessa teräksiin jäänyt austeniitti rekristallisoitui, mutta raerakenne muodostui epätasaiseksi koostuen reversion tuottamasta ultrahienoista rakeista ja jäännösausteniitin rekristallisaation tuottamista karkeammista rakeista. Sitä vastoin hehkutus 900 °C:ssa tuotti tasainen 2 μm austeniitin raekoon. Pitkissä hehkutuksissa korkeammissa lämpötiloissa 1000–1100 °C niobi-seostamattomissa teräksissä tapahtui hienojen rakeiden normaalia rakeenkasvua. Kuitenkin 0.28p-% niobi-seostuksen havaittiin oleva riittävä estämään rakeenkasvu. Reversion ja osittaisen rekristallisaation tuottamilla raerakenteilla saatiin erinomaiset myötölujuus-tasavenymäyhdistelmät. Vetokokeissa martensiitin ydintymispaikat ja -nopeus vaihtelivat monimutkaisella tavalla raekoosta riippuen

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Husák, Roman. "Pokročilé kompozitní konstrukční oceli pro použití v taveninách těžkých kovů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401604.

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Doctoral thesis was focused on preparing of new advanced ODS steels for use in heavy metal liquids enviroments. Possibility of new course for creating oxide dispersion in microstructure was verified by the course of internal oxidation of elements. By the internal oxidation method were prepared new ODS steels strengthened by complex oxides which were created by elements of IIIB and IVB group of elements. Based on analysis of damage ODS steels in LBE were designed surface protection of ODS steel by the oxide layer. The ODS steel protected by oxide layer was subjected to a corrosion test in LBE. For the experiments were chosen class of chromium steels: ferritic-martensitic steel 9Cr1WMnVTa and ferritic steels 14CrWTi and 17Cr1Mo. Steels without oxide dispersion and steel strenghtened by the dispersion based on Y-Ti-O oxides were prepared. On the steels were made series of mechanic tests which should reveal the effectivity of oxide dispersion on the strenght of steel prepared by the internal oxidation method and by the direct addition of oxide elements. It was found that significantly harder oxide material couldn't be fully disrupted through the mechanical alloying and fine oxide dispersion couldn't be created. There was verified fine oxide dispersion could be created by the internal oxidation method and by the direct adding of oxide elements. Same kind of steels strenghtened by new kind of complex oxides based on Y, Ce, Hf, La, Sc and Zr were prepared. The chemical analyses have proven that all added elements could created complex oxide by the reaction with yttrium. The computational analyses for observing of matrix influence and oxide phase influence on strenghtening of steels were performed. These computational analyses were based on microstructural analyses of ODS steels. There was found that the oxide particles could very effectively improve strenght of steels at room temperature and especialy at high temperature. Based on corrosion tests of 14Cr ODS steel in liquid Pb and LBE enviroment were designed surface protection of ODS steel. The effectiveness of protective layer was verified by the high temperature corrosion test of PM2000 in LBE. No damage of oxide layer was observed although Pb and Bi diffused through protective layer.

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Кравченко, В. С. "Дослідження процесу зносу деталей системи колінчастого вала та його впливу на ресурс та надійність автомобіля /комплексний проєкт/". Thesis, Чернігів, 2021. http://ir.stu.cn.ua/123456789/23218.

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Кравченко, В. С. Дослідження процесу зносу деталей системи колінчастого вала та його впливу на ресурс та надійність автомобіля /комплексний проєкт/ : випускна кваліфікаційна робота : 274 «Автомобільний транспорт» / В. С. Кравченко ; керівник роботи В. І. Кальченко ; НУ "Чернігівська політехніка", кафедра автомобільного транспорту та галузевого машинобудування. – Чернігів, 2021. – 130 с. В результаті проведеної роботи отримано значення певних показників систем та характеристик автомобіля; вони порівнювалися зі значеннями відповідно до прототипу та корегувалися таким чином, щоб досягти технічного та економічного ефекту в проектуванні. В першому розділі проведено аналітичний огляд легкових автомобілів модельного ряду ВАЗ та поставлені задачі щодо модернізації рульового керування. В другому розділі проводиться визначення масових показників та параметрів автомобіля та двигуна. За прийнятими геометричними параметрами автомобіля побудовано креслення «Загального вигляду автомобіля». В третьому розділі проведено розрахунок зовнішньої швидкісної характеристики двигуна, силового балансу автомобіля та визначення параметрів трансмісії. За результатами розрахунків побудовано креслення «Зовнішньої швидкісної характеристики двигуна та силового балансу». В четвертому розділі проведено розрахунок тягово-динамічних характеристик та побудовано креслення «Динамічних характеристик автомобіля». В п’ятому розділі проведено розрахунок гальмівних властивостей і паливної економічності автомобіля та побудовано креслення «Гальмівних властивостей і паливно-економічних показників автомобіля». В шостому розділі проведено розрахунок елементів рульового керування автомобіля-прототипу та побудовано схему «Рульове керування». В сьомому розділі проведено розрахунок модернізованого рульового керування. Результат модернізації зображений на креслені «Рульовий механізм». В восьмому розділі проведено дослідження вибору матеріалу і термообробки колінчастого вала. За результатами проведеної роботи зроблено висновок та сформовано пропозиції щодо вибору матеріалу і термообробки колінчастого вала. As a result of the work, the values of the parameters of the systems and the characteristics of the car were taken into account; The stench was corrected according to the meanings according to the prototype, which was corrected in such a rank, so that the technical and economical effect in the design was achieved. In the first section, an analytical survey of passenger cars of the VAZ model range was carried out and the tasks were set for the modernization of the steering wheel. In another section, the measurement of mass indicators and parameters of the car and engine is carried out. For the accepted geometric parameters of the car, the armchair "General view of the car" was prompted. In the third section, the development of the most important characteristics of the engine, the power balance of the car and the value of the parameters of the transmission were carried out. Based on the results of the calculations, the chair "External speed characteristics of the engine and power balance" was prompted. In the fourth section the calculation of traction-dynamic characteristics is carried out and the drawing "Dynamic characteristics of the car" is constructed. In the fifth section, the calculation of the braking properties and fuel efficiency of the car and a drawing of the "Braking properties and fuel and economic performance of the car." In the sixth section, the calculation of the steering elements of the prototype car and the scheme "Steering". In the sixth section, the calculation of the steering elements of the prototype car and the scheme "Steering". In the seventh section, the calculation of the modernized steering is performed. The result of the modernization is depicted in the drawing "Steering gear". In the eighth section, a study of the choice of material and heat treatment of the crankshaft. Based on the results of this work, a conclusion was made and proposals for the choice of material and heat treatment of the crankshaft were formed.

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Anttila, S. (Severi). "Influence of minor elements on some weldability issues of intermediate purity stabilized ferritic stainless steels." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526219738.

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Abstract Stabilized ferritic stainless steel grades are attractive alternatives to common austenitic grades in sheet metal applications. Compared with older unstabilized ferritic grades, the mechanical and corrosion properties are usually improved. The impurity level, mainly the amount of interstitial carbon and nitrogen, plays an important role in these steels. There are notable issues in the welding of these steels, the most apparent difference to austenitic steels is the susceptibility to brittle failure. This research focused on the influence of minor elements, especially aluminium, calcium, silicon, titanium, niobium, nitrogen and oxygen, on the weldability of modern intermediate purity level stabilized ferritic stainless steels. The research proceeded in several stages. At first, the general characteristics and performance data about the welds in currently manufactured 11 to 21 mass percent chromium ferritic stainless steels in Europe was obtained. The research then focused on novel high chromium stabilized ferritic stainless steels. Lastly, the influence of various steelmaking practices on weldability were investigated. The results showed that in stabilized ferritic stainless steels, slag islands are frequently seen in the molten weld pools. These islands can have many origins, e.g. deoxidation, calcium treatment and stabilization practices, and they can be roughly assessed from the chemical composition of the steel. The nature and the influence of these slags varies and can be related to irregularities in the weldability and molten metal fluid flow. Large grain size and titanium carbonitride particles impair the toughness of the heat-affected zone. Generally, stabilization with niobium is preferred. However, solely niobium stabilized steel welds run the risk of forming coarse columnar grains in welds deteriorating some of the properties. A breakdown of the columnar grains is possible to achieve in autogenous welds with minor titanium and aluminium alloying, provided that small amounts of nitrogen and oxygen are induced from the shielding gas. However, grain refinement may not improve the properties, if it is accomplished with an increase in the total interstitial content Tiivistelmä Stabiloidut ferriittiset ruostumattomat teräkset soveltuvat korvaamaan tavanomaisia austeniittisia ruostumattomia teräksiä ohutlevysovelluksissa. Näillä teräksillä keskeiset mekaaniset ja korroosio-ominaisuudet ovat usein paremmat kuin varhaisilla, stabiloimattomilla ferriittisillä teräksillä. Hiili ja typpi ovat näissä teräksissä kuitenkin epäpuhtauksia. Toisin kuin austeniittiset teräkset, ferriittiset teräkset ovat alttiita haurasmurtumalle, erityisesti hitsatuissa rakenteissa. Tässä väitöstutkimuksessa keskityttiin mikroseosaineiden ja epäpuhtauksien vaikutukseen keskipuhtaiden stabiloitujen ferriittisten teräslajien hitsauksessa. Tutkimus kohdistui erityisesti alumiinin, kalsiumin, piin, titaanin, niobin, typen ja hapen vaikutuksiin. Aluksi tutkittiin kaupallisten terästen hitsien keskeisiä ominaisuuksia. Tämän jälkeen tutkittiin uusia ns. korkeakromisia stabiloituja ferriittisiä teräslajeja. Lopuksi tutkittiin teräksen valmistuksen vaikutuksia stabiloitujen ferriittisten ruostumattomien terästen hitsattavuuteen. Tutkituilla teräksillä hitsauksen aikana muodostui runsaasti kuonalauttoja. Näillä kuonilla on monta alkuperää, esim. deoksidointi, kalsiumkäsittely ja stabilointiaineet. Hitsien kuonaisuutta voidaan karkeasti arvioida teräksen kemiallisen koostumuksen perusteella. Muodostuvilla kuonilla on useita vaikutuksia hitsauksessa, mm. epäjatkuvuuksiin ja sulan virtauksiin. Hitsauksessa muodostuva suuri raekoko ja stabiloinnin titaanikarbonitridipartikkelit heikentävät oleellisesti hitsin muutosvyöhykkeen sitkeyttä. Stabilointi käyttäen pääasiassa niobia on toivottavaa, mutta jos stabilointiin käytetään vain niobia, tulee hitsin mikrorakenteesta karkea ja hitsin ominaisuudet voivat heikentyä. Karkean mikrorakenteen hienontaminen on mahdollista käyttäen suojakaasuna argonia, jossa on hieman typpeä ja happea, mikäli teräkseen on seostettu hieman alumiinia ja titaania. Raerakenteen hienontaminen ei kuitenkaan yksiselitteisesti paranna hitsin ominaisuuksia, mikäli hienontaminen saavutetaan kasvattamalla epäpuhtauspitoisuutta tarpeettoman korkeaksi

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21

Hausmann, Katharina [Verfasser], Ewald [Akademischer Betreuer] Werner, and Wolfgang [Akademischer Betreuer] Bleck. "TRIP-assisted Thin Sheet Steel with a Bainitic and/or Martensitic Matrix : Effects of Alloying Elements and Heat Treatment on Phase Transformations, Microstructures, and Mechanical Properties / Katharina Hausmann. Gutachter: Wolfgang Bleck ; Ewald Werner. Betreuer: Ewald Werner." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/107165148X/34.

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Hausmann, Katharina Verfasser], Ewald [Akademischer Betreuer] [Werner, and Wolfgang [Akademischer Betreuer] Bleck. "TRIP-assisted Thin Sheet Steel with a Bainitic and/or Martensitic Matrix : Effects of Alloying Elements and Heat Treatment on Phase Transformations, Microstructures, and Mechanical Properties / Katharina Hausmann. Gutachter: Wolfgang Bleck ; Ewald Werner. Betreuer: Ewald Werner." München : Universitätsbibliothek der TU München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20150430-1232002-1-0.

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23

Evin, Harold. "Low Cr alloys with an improved high temperature corrosion resistance." Thesis, Dijon, 2010. http://www.theses.fr/2010DIJOS082/document.

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Les aciers ferritiques à faible teneur en chrome tel que le T/P91 sont largement utilisés dans les centrales de productions d’électricité pour leurs bonnes propriétés mécaniques et leur faible coefficient d’expansion thermique. Cependant, la demande croissante en énergie alliée à la nécessité de réduire les émissions de gaz à effet de serre, conduisent à envisager l’augmentation des conditions d’utilisation (température et pression) de ces matériaux. Des études ont montré qu’en modifiant la température de fonctionnement et la pression de vapeur d’eau de 538°C/18.5 MPa à 650°C/30 MPa, le rendement des centrales thermiques progressait d’environ 8%. Se pose alors la question de la tenue à la corrosion à haute température des aciers à 9% de chrome. Au cours de ces travaux, le comportement d’un acier ferritique/ martensitique à 9% de chrome a été étudié à 650°C sous air sec et sous vapeur d’eau de matière isotherme et en conditions de cyclage thermique. La prise de masse des échantillons renseigne sur la cinétique de la réaction d’oxydation et l’adhérence des couches d’oxydes formées. Les produits de corrosion ont été caractérisés par plusieurs techniques d’analyses dans l’optique de clairement identifiés les oxydes en présences et leurs mécanismes de formation. Des oxydes mixtes de fer et de chrome (Cr,Fe)2O3 sont dans un premier temps formés et assurent s’avèrent être temporairement protecteur. Pour des longs temps d’oxydation ou des températures supérieures à 650°C, la magnétite Fe3O4 et l’hématite Fe2O3 sont les principaux oxydes formés, montrant ainsi l’inadéquation des nuances à faible teneur en chrome pour une utilisation dans des conditions aussi drastiques. Dans l’optique d’augmenter la résistance à la corrosion à haute température de cet alliage, diverses solutions ont été envisagées tel que l’aluminisation par cémentation en caisse, les revêtements d’oxydes de terre rare par MOCVD, ou encore l’ajout d’éléments d’addition. Ces solutions ont été également testées à 650°C sous air sec et sous vapeur d’eau The improvement of high temperature oxidation resistance of low chromium content steels, such as T/P91, is of great interest in regards with their application in thermal power generating plants. Indeed, they possess good creep properties, and low thermal expansion coefficient. Important needs in energy together with environmental issues place power generation plants under constraints which lead to develop high efficiency systems. A usual way to increase the efficiency consists in increasing temperature and pressure parameters of the power generating plant. Studies has shown that the total efficiency of a plant increases by nearly 8 % when changing the steam parameters from 538°C/18.5 MPa to 650°C/30 MPa. Then, the problem of corrosion resistance of 9% chromium steel in those conditions is asked. In this work, the behavior of a ferritic / martensitic 9% chromium steel has been studied at 650°C in dry air and in water vapor containing environment in both isothermal and thermal cyclic conditions. The weight gain of samples provides information on the kinetics of the oxidation reaction and the adhesion of formed oxide scale. Corrosion products were characterized by several analytical techniques in order to identify oxides with accuracy and to understand their formation mechanisms. Mixed iron and chromium oxides (Cr, Fe) 2O3 are initially formed and provide temporary protection to the substrate. For long time exposure or temperatures above 650°C, magnetite, Fe3O4 and hematite Fe2O3 are the main oxides formed, highlighting the fact that low chromium steel are inappropriate for applications in such drastic conditions. In order to increase the high temperature corrosion resistance of this alloy, various solutions have been proposed as aluminizing by pack cementation, reactive element oxides coatings of by MOCVD, or addition of alloying elements in the steel composition. These solutions were then tested at 650 ° C in dry air and in water vapor environments

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Yonekubo, Ariane Emi. "Caracterização microestrutural do aço inoxidável superdúplex UNS S32520 (UR 52N+) processado por moagem de alta energia." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2010. http://tede2.uepg.br/jspui/handle/prefix/1399.

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Made available in DSpace on 2017-07-21T20:42:33Z (GMT). No. of bitstreams: 1 Ariane Emi Yonekubo.pdf: 14387414 bytes, checksum: 915c8e68747eb2fccc91d9829eb93469 (MD5) Previous issue date: 2010-09-10 Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná Superduplex stainless steels are often used in applications where is necessary high mechanical strength combined with corrosion resistance. They are formed by a ferrite (a) BCC and austenite (g) FCC mixture, have a yield stress about of the double of the austenitic and ferritic stainless steels, larger plasticity that the one of the martensitic and precipitation hardening, high resistance to the intergranular corrosion, pitting and the stress-corrosion cracking. However, during hot deformation, these steels recrystallize forming a lamellar microstructure with anisotropic properties. Through the high energy milling, accomplished with Spex, Attritor and Planetary ball mills, it was aimed to obtain a homogeneous and with fine grains superduplex stainless steel. Initially, in this work, chips were made by machining of a UR 52N+ (UNS S32520) commercial superduplex stainless steel rolled sheet, without previous heat treatment, which will be submitted to the high energy milling adjusting the milling parameters and subsequently it was accomplished the heat treatment at temperatures of 1200 °C e 1250 °C for 1 hour in argon atmosphere and 1200 °C for 1 hour in argon with 2% of hydrogen. The obtained powders were analyzed by scanning electron microscopy, observing that the smaller and more homogeneous particles were obtained by Spex milling for 16 and 32 hour; the compressibility curve showed that after a long time milling, the material can present compaction difficulty and this way, great final porosity. The x ray diffraction presented peaks with a bottom widening due to the small size of the obtained particles. The porosity percentage determined by optical microscopy, reduced after heat treatment at 1200 °C in argon atmosphere with 2% hydrogen, however the scanning electron microscopy showed a fine porosity that could not be observed only in the optical microscopy analysis. The differential scanning calorimetry and the differential thermal analysis showed formation and revertion of strain induced martensite peaks and using atomic force microscopy, magnetic ferrite and paramagnetic austenite phases were observed by a non destructive test. The milling of the chips in Spex milling for 16 hours provided a refined microstructure with equiaxial grains and size of 11 μm after heat treatment at 1200 °C for 1 hour in argon atmosphere. Aços inoxidáveis dúplex são frequentemente utilizados em aplicações onde é necessária elevada resistência mecânica combinada a resistência à corrosão. São formados por uma mistura de ferrita (a) CCC e austenita (g) CFC, apresentam limite de escoamento cerca de o dobro dos aços inoxidáveis austeníticos e ferríticos, maior plasticidade que a dos martensíticos e dos endurecíveis por precipitação, elevada resistência à corrosão intergranular, à corrosão localizada e à corrosão sob tensão. Porém, durante a deformação a quente, estes aços recristalizam-se formando uma microestrutura lamelar com propriedades anisotrópicas. Através da moagem de alta energia, realizada com moinhos de bolas dos tipos Spex, Attritor e Planetário, objetivou-se obter um aço inoxidável superdúplex de grãos homogêneos equiaxiais e finos. Inicialmente, neste trabalho, foram feitos cavacos por usinagem da chapa laminada de um aço inoxidável superdúplex comercial UNS S32520 (UR 52N+), sem tratamento térmico prévio, os quais foram submetidos à moagem de alta energia acertando-se os parâmetros de moagem e posteriormente realizou-se o tratamento térmico em temperaturas de 1200 °C e 1250 °C, por tempo de 1 hora em atmosfera de argônio, e a 1200 °C por 1 hora em atmosfera de argônio com 2% de hidrogênio. Analisaram-se os pós obtidos por microscopia eletrônica de varredura, observando que as partículas menores e mais homogêneas foram obtidas após as moagens no Spex por 16 e 32 horas; a curva de compressibilidade mostrou que após um tempo muito grande de moagem, o material pode apresentar dificuldade de compactação e desta maneira, maior porosidade final. A difração de raios x apresentou picos com alargamento na base devido ao tamanho pequeno de partículas obtidas. A porcentagem de porosidade, determinada por micrografia óptica, diminuiu após tratamento térmico a 1200 °C em atmosfera de argônio com 2% de hidrogênio,porém a microscopia eletrônica de varredura mostrou uma porosidade fina que não pôde ser observada somente através da microscopia óptica. As análises térmicas por calorimetria exploratória diferencial e por análise térmica diferencial mostraram picos de formação e reversão de martensita induzida por deformação e pela microscopia de força atômica, foram observadas as fases ferrita magnética e austenita paramagnética por ensaio não destrutivo. A moagem dos cavacos em moinho do tipo Spex por 16 horas forneceu uma microestrutura refinada com grãos equiaxiais e tamanho de 11 μm após tratamento térmico a 1200 °C por 1 hora em atmosfera de argônio.

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Sandberg, Natalia. "On the Machinability of High Performance Tool Steels." Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-172427.

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The continuous development of hot forming tool steels has resulted in steels with improved mechanical properties. A change in alloying composition, primarily a decreased silicon content, makes them tougher and more wear resistant at elevated temperatures. However, it is at the expense of their machinability. The aim of this study is to explain the mechanisms behind this negative side effect. Hot work tool steels of H13 type with different Si content were characterised mechanically, and evaluated analytically and by dedicated machining tests. Machining tests verified that materials with low Si content displayed reduced machinability due to their stronger tendency to adhere to the cutting edge. Three hypotheses were tested. The first hypothesis, that the improved toughness of the low Si steels is the reason behind their relatively poor machinability, was rejected after machining tests with one low Si steel heat treated to the same relatively low toughness as conventional hot work tool steels. The second hypothesis, that a change in oxidation properties, also associated with the change in Si composition, lies behind the reduced machinability was investigated by dedicated tests and evaluations. It was found that the oxide thickness increased with reduced Si content and that there was an enrichment of Cr at the oxide/steel interface. The differences in oxide thickness and the possible differences in oxidation properties may influence the machinability of the materials through their different abilities to adhere to the cutting edge. The third hypothesis, that a high enough temperature to initiate phase transformation from ferrite to austenite is generated during machining of the tool steels, was also investigated. This may lead to a reduced machinability because higher austenite content is directly related to higher compressive stresses and higher cutting forces. This causes accelerated tool wear. This hypothesis was verified by ThermoCalc calculation of austenite content in the steels, which showed a good agreement with Gleeble compression tests and cutting force measurements. This thesis confirms that a reduced Si content in conventional H13 steel improves the toughness, reduces the oxidation resistance and lowers the ferrite-to-austenite transformation temperature. The reduction in austenite temperature is probably the most important factor behind the reduced machinability.

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McGinnis, Alexander L. "Diffusion Couple Alloying of Refractory Metals in Austenitic and Ferritic/Martensitic Steels." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6832.

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This thesis utilized the diffusion couple approach to evaluate the addition of molybdenum, niobium, tantalum, and tungsten to 316 stainless (316SS) and alloy HT9 steels. Refractory elements have been previously studied as alloying candidates to mitigate problems such as radiation-induced segregation, void swelling, and irradiation creep in reactor steels. Diffusion couples were characterized via energy dispersive x-ray spectroscopy (EDS) and nanoindentation to examine refractory element solubility, diffusivity, and the effects these elements have on hardness and elastic modulus in 316SS and alloy HT9. Molybdenum and tungsten samples showed significantly higher solubility and diffusivity than niobium and tantalum, with evidence of multiphase regions several hundred microns from the diffusion couple interface. Nanoindentation revealed evidence of hardening as a function of increasing concentration for some, but not all of the refractory elements. Diffusion of the refractory elements in alloy HT9 was significantly higher than in 316SS, which suggests that alloy HT9 retained its ferritic structure even at high temperatures, i.e., 1100C.

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Emenike, Cornelius O. I. "The effects of alloying elements on the properties of pipe line steels." Thesis, Aston University, 1987. http://publications.aston.ac.uk/11927/.

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Lai, Libang. "Low temperature embrittlement of duplex stainless steels : A study of alloying elements’ effect." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289565.

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Duplex stainless steels (DSSs), consisting of an equal amount of ferrite and austenite phases, have wide applications in e.g. vehicles, chemical engineering as well as nuclear plant because of the combination of excellent mechanical properties and corrosion resistance. However, low temperature embrittlement has existed for a few decades restricting the application of DSSs over about 250 ºC. When the service temperature ranges from around 250 to 500 °C, DSSs would become brittle because of the phase separation in the ferrite phase. The phase separation is the main reason for the low temperature embrittlement, and the kinetic of this phase separation achieves the fastest rate at about 475°C, so it is also termed as ‘475°C embrittlement’. Plenty of research has been performed in this field, but the problem remains. The mechanism of phase separation is due to the existence of a miscibility gap in the iron chromium binary system, and previous research has reported some alloying elements can have the potency to delay the phase separation and the goal of my thesis is to investigate the influence of different alloying elements and select one which could be a plausible one to retard phase separation, and subsequently try to mitigate the low temperature embrittlement problem of DSSs. This work includes the literature survey of different alloying elements which could influence the microstructure and mechanical properties of DSSs in general. Subsequently the thermodynamic calculation was performed to identify the effect of the selected alloying elements addition on phase formation during heat treatment. Vanadium was selected to be a potentially suitable alloying element to be added into DSSs and experimental investigations were performed on the heat treatment process and the effect of V alloying. The main conclusions of the proposed thesis can be drawn as follow: The elemental addition of Al, Si, V, Nb and Ti are calculated by Thermo-Calc, they are all ferrite stabilisers and V addition seems most likely to be effective due its combination with the interstitial elements C and N. In the experimental part, vanadium additions combined with intermediate temperature solution treatment could be effective to retard the age hardening effect and the impact toughness test has a consistent tendency. Also, according to Thermo-Calc calculations and experimental results, the more interstitial elements that combine with V and precipitate from the ferrite phase the better was the performance of the duplex stainless steels. Duplexa rostfria stål (DSS), bestående av lika stor mängd ferrit- och austenit, har bredtillämpning inom t.ex. fordon, kemiteknik samt kraftverk på grund av kombinationen av utmärkta mekaniska egenskaper och korrosionsbeständighet. Försprödning vid låg temperatur begränsar emellertid tillämpningen av DSS över 250 °C. När driftstemperaturen varierar från cirka 250 till 500 ° C så kan DSS bli spröda på grund av fasseparation i ferritfasen. Fasseparationen är den främsta orsaken till lågtemperaturförstöring, och kinetiken för denna fasseparation uppnår den snabbaste hastigheten vid cirka 475 °C, så den kallas också '475 °C-försprödning'. Mycket forskning har utförts inom detta område, men problemet kvarstår. Mekanismen för fasseparation beror på förekomsten av ett blandningslucka i det binära järn-krom-systemet, och tidigare forskning har rapporterat att vissa legeringselement kan ha förmågan att fördröja fasseparationen. Målet med mitt examensarbete är att undersöka påverkan av olika legeringselement och välja ett som kan användas för att fördröja fasseparationen och därav mildra problemet med lågtemperaturförsprödning hos DSS. Detta arbete inkluderar litteraturundersökning av olika legeringselement som kan påverka mikrostrukturen och mekaniska egenskaper hos DSS i allmänhet. Därefter termodynamiska beräkningar för att identifiera effekten av de valda legeringselementen på fasjämvikt under värmebehandlingen. Vanadin valdes som ett potentiellt lämpligt legeringselement som kan tillsättas i DSS. Experimentella undersökningar utfördes på värmebehandlingsprocessen och effekten av V-legering. De huvudsakliga slutsatserna av examensarbetetär: tillsatsen av Al, Si, V, Nb och Ti beräknades av Thermo-Calc, de är alla ferritstabiliserande och V-tillsats verkar kunna vara effektiv på grund av dess kombination med de interstitiella elementen C och N. I den experimentella delen studerades vanadintillsatser i kombination med värmebehandling för att fördröja den hårdnandet och försprödningen. Enligt Thermo- Calc-beräkningar och experimentella resultat så kan prestanda förbättras desto merinterstitiella element som kombineras med V.

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Kubíček, Antonín. "Vliv podmínek mechanického legování na kontaminaci práškových směsí a bulk materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-416663.

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This thesis deals with the influence of process parameters on the contamination level of powder materials produced by mechanical alloying (MA) technology. For this purpose austenitic stainless steel 316 L and equiatomic CoCrFeNi high-entropy alloy (HEA) were prepared by high-energy ball milling. Both materials were milled in argon and nitrogen atmospheres from 5 to 30 hours. Spark plasma sintering method (SPS) was then used for consolidation of chosen powder samples. Chemical analysis of contamination within MA was carried out using combustion analysers for determination of carbon, oxygen, and nitrogen contents after different lengths of milling. Also differences in chemical composition of powder and corresponding bulk samples were measured. The microstructure analysis using scanning electron microscopy (SEM) of both powder and bulk materials was executed with focus on oxide and carbide presence and dispersion. Increasing content of carbon with increasing milling time was observed across all measured samples. This contamination is attributed to using milling vial made of tool steel AISI D2 (containing 1,55 wt. % of carbon). Increase of carbon content within consolidation using SPS was also observed. Milling of specimens using N2 as milling atmosphere caused higher contamination level in both AISI 316 L and HEA compared to milling in argon.

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PANELLI, RENATO. "Processamento do aco AISI M2 com adicao de 10 porcento vol. NbC utilizando a tecnica de mechanical alloying." reponame:Repositório Institucional do IPEN, 1999. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10748.

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Made available in DSpace on 2014-10-09T12:43:36Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T13:58:20Z (GMT). No. of bitstreams: 1 06531.pdf: 4466032 bytes, checksum: a6e28ab0187aa788035c1d0e3ed8764f (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Dissertacao (Mestrado) IPEN/D Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP FAPESP:96/08958-1

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31

Walser, David Jordan. "Investigating the Relationship Between High Temperature Flow Stress and Friction Stir Weldability in HSLA Steels." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5943.

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The feed rate at which a defect free friction stir weld can be run (friction stir weldability) on an HSLA steel plate can vary widely between heats that meet the same specified physical properties. Consequently, every time a new heat of HSLA steel is obtained, exploratory welds must be run to determine the proper feed rate for that plate. Previous research suggests that the varying levels of alloying elements related to high temperature physical properties between the different heats causes the observed change in friction stir weldability. Because of this, it was hypothesized that the high temperature physical properties of HSLA steels are related to their friction stir weldability.High temperature physical propeties of HSLA steels are a function of the alloying content of the steel. To determine the relationship between high temperature physical properties and alloying content, eight different heats of HSLA steel with different chemical compositions were obtained. In particular, percent additions of molybdenum, vanadium, niobium, and titanium were varied between the heats in a factorial design. Gleeble compression tests were run on each heat to determine their high temperature properties. Based on these tests, experimental models wereconstructed to estimate the high temperature properties of HSLA steels based on composition and temperature. These models were used to determine the high temperature physical properties of HSLA heats with known friction stir weldability. The high temperature physical properties werecompared to the friction stir weldability of each heat. No correlation was found in this study between the high temperature properties examined and friction stir weldability in HSLA steels.

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32

Guo, Xiaofei [Verfasser]. "Influences of Microstructure, Alloying Elements and Forming Parameters on Delayed Fracture in TRIP/TWIP-Aided Austenitic Steels / Xiaofei Guo." Aachen : Shaker, 2012. http://d-nb.info/1066197296/34.

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Daniel, Geoffrey Morrall. "Evaluation of material properties of mechanically alloyed SUS304L with Zr addition." Kyoto University, 2019. http://hdl.handle.net/2433/242327.

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34

Pech, Filip. "Nové kompozice pokročilých oxidicky zpevněných ocelí na bázi prvků vzácných zemin." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318785.

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The main objective of present diploma thesis is to prepare three different classes of steels, differing by their content of chromium: 9Cr, 14Cr, 17Cr steels and their oxide dispersion strengthened variants. Steels were prepared from atomic and pre-alloyed powders by the mechanical alloying and compacted by the spark plasma sintering method. Used strengthening elements were yttrium, which is most commonly used, and aluminium. Preparation of oxide dispersion was done in two ways: direct adding of yttria and alumina and inner oxidation of aluminium and yttrium. In the experimental part has been found, that it is possible to make oxide dispersion by both ways, but aluminium strengthened steel has to be prepared by inner oxidation to ensure fine oxide dispersion.

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35

Saikoff, Elsa, Edvin Andersson, Felix Bengtsson, et al. "Cobalt in High Speed Steels." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355124.

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One of the most important additives in High Speed Steels (HSS) is cobalt, mainly for its effect on the hot properties. Based on statistic data about the increased price of cobalt and its negative effect on human health, an ethical and financial barrier in the steel industry have occurred. In order to solve the problem, it is of great importance to examine the future cobalt price and accessibility, as well as examine the possibility of finding alternative substitutes to cobalt. The purpose of this project was therefore to examine alternatives to cobalt as an alloying element in HSS. A qualitative literature study was performed by analyzing the economy of cobalt, studying the main reasons for cobalts tendency to improve the hot properties of the steel and finding alternative elements to replace, or at least reduce, cobalt in HSS without degrading the hot properties. Cobalt is used both in the chemical and metallurgical business. But the demand of cobalt is largely driven by chemical purposes with the focus on its rechargeable battery applications. The analysis shows that there is nothing pointing at a significant decrease of the price of cobalt. Lithium ion batteries stands for about 50% of current cobalt supply, which is why the price has surged the recent years. The market for electric vehicles and rechargeable batteries has skyrocketed. To decrease the price of cobalt, a substitute for cobalt in rechargeable batteries would need to be found, which is not very likely for the time being. The effect of cobalt in HSS is mainly on the red hardness and tempering resistance. Cobalt increases the bonding strength in the steel matrix and changes the microstructure of the finer secondary carbides. Also the growth rate and coalescence rate of the carbides decreases. This causes the red hardness and the tempering resistance to increase. To replace cobalt, several alternative alloying elements have been researched. Among the most promising are niobium, nitrogen and aluminium, where niobium were found to be of most interest, due to the broad support of relevant articles in the field of powder metallurgical processing. The positive effect of niobium could be regarded as three-fold. The first contribution is the refinement of grain size and homogeneity of the primary carbides, which increases the overall hardness. The second effect is that the addition of niobium shifts the phase equilibria in such a way that the precipitation of primary carbides mainly will be in the form of hard and stable NbC. The majority of the other alloying elements will hence be precipitated as secondary carbides during tempering. The final effect is an increase in secondary hardness, as a consequence of the large amounts of vanadium and smaller amounts of niobium that is being precipitated during tempering to the secondary carbides. This enables a high matrix hardening potential in the optimal state of tempering.

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36

Hamada, A. S. (Atef Saad). "Manufacturing, mechanical properties and corrosion behaviour of high-Mn TWIP steels." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514285844.

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Abstract Austenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique. The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes. The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired. Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution.

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ARAUJO, EDVAL G. de. "Efeito das adicoes de portadores de fosforo e da alumina na sinterizacao do aco rapido M2." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10766.

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Made available in DSpace on 2014-10-09T12:43:48Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T14:09:59Z (GMT). No. of bitstreams: 1 06776.pdf: 13953559 bytes, checksum: fbb8c77f5b5bada8939f5c8e246ef8e6 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Tese (Doutoramento) IPEN/T Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP FAPESP:95/03947-9

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38

Barguet, Laurianne. "Contrôle acoustique et vibratoire de la mécano-synthèse des matériaux composites à matrice métallique nanostructurés." Thesis, Le Mans, 2015. http://www.theses.fr/2015LEMA1027/document.

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Lors de la synthèse des aciers ODS, la première étape consiste à réaliser un broyage actif, appelé mécano-synthèse, entre les matériaux de départ qui sont la poudre métallique et les renforts d’oxyde. Ce procédé peut se réaliser au moyen d’un broyeur à boulets, constitué d’une cuve cylindrique à l’intérieur de laquelle des billes en acier sont introduites. Le broyage résulte des combinaisons de chocs entre billes, poudre et paroi de la cuve, ce qui conduit à une évolution de la de la taille, de leur forme et de leur polydispersité. La première partie de cette thèse s’est attachée à élaborer un moyen de caractérisation de la poudre par des mesures ultrasonores. Une méthode qui consiste à sonder un échantillon de poudre métallique pour la mesure des paramètres acoustiques s’est avérée être adaptée pour la qualification de la poudre métallique en cours de broyage. Une dépendance des paramètres acoustiques avec les caractéristiques morphologiques du milieu a également été mise en évidence pour des échantillons granulaires. Dans une deuxième partie, l’optimisation du procédé par l’identification de la vitesse optimale de rotation de la cuve est recherchée dans un premier temps. Une mise en parallèle des signaux acoustiques et vibratoires en fonction de la vitesse de rotation de la cuve avec le mouvement des billes, montre que les énergies acoustique et vibratoire sont des indicateurs pouvant conduire à la vitesse de rotation optimale. Puis, il est montré comment des mesures acoustiques et vibratoires durant un broyage permettent de caractériser l’évolution de la nature des poudres et d’identifier la présence de colmatage de la poudre sur les parois de la cuve During the ODS steel (Oxide Dispersion Strengthened) synthesis, the first stage consists in an active milling between original materials, which are metallic powder and oxide to obtain reinforced micro/nanoscale dispersions. This process, known as mechanical alloying, could be realized by balls milling composed by a cylindrical tank rotating around its main axis, within which steel beads are introduced. The grinding results from different combinations of collisions between beads and powders on the tank walls, that lead to morphological grain powder evolution (grain size and shape). The first part of this thesis proposes an ultrasonic method to characterize the metallic powder. An experimental method, which consists in acoustic probing for measuring linear acoustic parameters (longitudinal wave velocity and elastic modulus) of a slab of powder sample, appears to be suitable to follow different mechanical alloying stages. A dependence of the acoustic parameters on the morphological characteristics of metallic powder (grain shape and grain size distribution) is shown with the same sample preparation and the same confining pressure. In the second part, optimization process by identification of ball milling optimal rotation speed is researched in a first step. Correlation between acoustic or vibration signals and bead motion versus rotation speed, shows that acoustic and vibration energy are good indicators that can be used to find the optimal rotation speed. In a second step, acoustic and vibration measures are used to follow grain material properties evolution during a grinding (for a period of 176hrs) and to identify powder clogging mechanism on a milling tank

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39

Shieh, Cheng-Hung, and 謝政宏. "Laser Surface Alloying of Stainless Steel with Silicon Nitride." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/53919229607451551214.

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40

Adebiyi, Damilola Isaac. "Laser surface alloying of martensitic stainless steel for improved service performance." Thesis, 2012. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000185.

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M. Tech. Metallurgical Engineering Martensitic stainless steel (MSS) metal matrix composite coatings that can accommodate most applications were developed using TiC and stellite 6 as reinforcement powders and Nd: YAG solid state laser for surface alloying. The alloyed surfaces were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). The microstructures of the alloyed zones show even distribution and super saturation of titanium carbide and other complex carbides of chromium (Cr23C6), niobium (Nb6C5), and iron (Fe7C3) in the matrix of the MSS A significant increase in the hardness was achieved by the addition of stellite 6, although with cracks in the alloyed layer. The cracks formation was due to high heat build-up during the laser alloying process. As a result of the addition of TiC powder in the form of premixed ratio, the heat build-up in the work-piece was minimized. This is due to the high absorptance of laser irradiation by the TiC powder. The alloyed zone of the premixed ratio was free from cracks with microhardness increase of more than 150% of that of the substrate. Multiple tracks of 50% and 75% overlap were fabricated. Three-body abrasive wear study of the overlapped coatings revealed the wear mechanism of the laser coatings to be adhesion, mild abrasive and less degree of deformation showing less plastic ploughing and cutting compared to the as-received. The wear mechanism of the as-received is adhesion, severe abrasive and plastic deformation, showing distinct grooves and damaged spots in the form of craters. The wear resistance of the MMC obtained by alloying with the TiC powder was significantly improved with the 75% overlap, about 90% better than the native material.

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Chang, Ya-Ling, and 張雅齡. "The Analysis of Lenticular Martensite Submicron Structure in AISI 440C Alloying Steel." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/54775878294644411087.

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博士 國立臺灣大學 材料科學與工程學研究所 103 This work mainly focuses on the investigation of the microstructure and transformation of lenticular martensite in AISI 440C stainless steel. The research can be divided into two parts. The goal of the first is to analyze the transformation and morphology of lenticular martensite; the goal of the second is to observe the evolution of carbide formation in lenticular martensite during tempering treatment. In the first part, by controlling the homogenization temperature, an appropriate lenticular martensite structure was obtained, facilitating the following observation. The influences of the alloying element content on Ms temperature and the transformed martensite morphology were analyzed with electrical microscopy. Due to the high alloying element content of AISI 440C stainless steel, even after homogenization treatment, the M7C3 carbides are still distributed in the austenite matrix and therefore become the nucleation sites of lenticular martensite. During the martensite transformation process, the initial nucleation product is plate martensite, which then grows into a lenticular martensite structure. Lenticular martensite contains three regions: a midrib (which can be seen as the former plate martensite structure), a twinned region, and an untwinned region. These three regions differ not only in their morphologies but also in their misorientation distribution. Transmission election microscopy (TEM) and electron backscatter diffraction (EBSD) techniques were applied to explore the misorientation in these regions and the crystal orientation relationship between austenite and martensite. In our observations, a single lenticular martensite grain shows an elliptical morphology. Furthermore, a specimen polished with the focus ion beam (FIB) method provides 3-D images information and confirms that lenticular martensite is shaped like a thick shell. The crystallography of lenticular martensite formed in coarse austenite grains was investigated using electron backscattered diffraction (EBSD). Although the spread in diffracted intensity within pole figures was significant, due to the orientation gradient within lenticular martensite, the trend of pole figures indicated that the lenticular martensite approximately adopted a Kurdjumov-Sachs (K-S) orientation relationship with respect to the austenite matrix. The orientation relationships of variant pairings (zigzag, spear, and kink types) have been analyzed. The aim of the second part of this research is to discuss the effects of tempering treatment on lenticular martensite. After tempering at 400ºC, there exist two different kinds of cementite: the "needle" type, which does not transform into M7C3 even after a long tempering treatment, and the "rice" type, which first nucleates at twins in the midrib region and dislocations in the untwinned region, continues to grow during tempering treatment, and finally becomes a parallelogram-shaped M7C3 carbide. The discrepancies between the two types of cementites in shape and crystallographic relationship can be attributed to the nucleation and growing mechanisms. With electrical microscopy analysis, the displacive mechanism and diffusion mechanism are applied to elucidate the formation of cementites in lenticular martensite.

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42

huang, Kuiyu, and 黃奎育. "Processing of TiC dispersion strengthened 304 stainless steel composite alloy by mechanical alloying." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/mg4c26.

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碩士 國立臺北科技大學 材料及資源工程系研究所 98 304 stainless steel Austenitic stainless steel stress due to heat and stress effects phase transformation. Deformation at room temperature will cause the process of martensite phase change, then, and then make the appropriate changes in return to heat treatment will change back to austenite. In this study, the alloy by mechanical means to try to observe the phase change of 304 stainless steel powder, and add the TiC strengthening phase, the mechanical properties of the difference. In this experiment, planetary ball milling 304 stainless steel powder form, using stainless steel milling tank(250 ml) and balls (5 mm) with BPR 15:1, milling speed of 400 rpm, at different milling time: 0,2,4,6,8,10 hours, and with XRD, SEM and laser particle size analyzer of observed the changes in 304 stainless steel powder. In addition to planetary ball mill to steel powder and TiC powder mixture, using stainless steel milling tank(250 ml) and balls (5 mm) by 400 rpm, milling time：0, 6,10 hours, the ratio of TiC powder were 0 %, 10% weight percentage (equivalent to about 15% volume percentage). With XRD, SEM, density and hardness of the differences between the mechanical properties observed. The results showed that the milling time 2,4,6 小時 of 304 stainless steel powder, with the increase of plastic strain, so that by the austenitic microstructure to martensite. Milling time 8,10 小時 of 304 stainless steel powder, with increasing temperature, to bring the organization back into austenite. Found that the milling time 6,10 hours of 304 +10 wt% TiC composite alloy sintered at 1335℃ temperature and holding temperature 2 hours under vacuum sintering relative density of 98% to high density. Shows that, after the ball milling process of the strengthening phase TiC effective dispersion strengthening phase in 304 stainless steel base, effectively hinder dislocation slip, significantly improve their mechanical properties.

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Li, Kuen-Da, and 李昆達. "Processing of TiC Dispersion Strengthened 440C Stainless Steel Composite Alloy by Mechanical Alloying." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/xkxz92.

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碩士 國立臺北科技大學 材料科學與工程研究所 95 The composite powders that 440C high chromium stainless steel with different amounts (25, 35 and 45vol.%) of TiC has been successfully produced by Mechanical alloying Method. As a result in experiment when milling speed fixed on 600rpm, BPR80 and temperature control is under 30℃, the composite powders were form within 16hr. Then the composite powders were shaping and vacuum sintered at 1200, 1300 and 1400℃, followed by HIP processes. Finally, the composite alloys were form. Various materials characterization techniques were used in order to evaluate the materials properties and microstructures, including apparent porosity, hardness test, transverse rupture strength (TRS) test, XRD and SEM. The results show that a high hardness was obtained when the 35vol.% TiC composite powder was sintered at 1400℃. a high TRS value was obtained when the 25vol.% TiC composite powder was sintered at 1200℃.

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Wu, T. L., and 吳宗樑. "The microstructure of laser alloying high speed steel with nickel coated aluminium powder." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/05890472246946524150.

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碩士 國立臺灣科技大學 機械工程研究所 83 A 1500 W CW-CO2 laser was used to surface remelt and alloy nickel coated aluminum powder on W-Mo-Co high speed steel , then post heat treated at 560 ℃ for two hours and three times. Optical metallography (OM) , scanning electron microscope (SEM) , Vicker's microhardness (Hv) , energy- dispersive spectrometer (EDS) , electron probe microanalyzers (EPMA , and transmission electron mircroscope (TEM) were employed to characterize the remelted and alloyed layer. The microstructure of the remelted layer was a preponderance of cells. The hardness of laser=remelted layer was increased from 750-900Hv to 1100-1200Hv and the alloyed layer was increased from 550Hv to 620Hv after the 560 ℃ post heat treatment. And the EDS and EPMA results reveal that the cells were composed of Fe,Al,Ni and the cellular seregaations of W,Mo,V,Cr were observed in the laser-alloyed zone. And from the electron diffraction crystal structure determination , a B2 (Fe,Ni)Al superlattice structure was identified and its lattice parameter is 2.876A.

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CHEN, ZHI-MING, and 陳志明. "A study on surface alloying of high-Mn steel by plasma transferred Arc melting." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/30761091523663201547.

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Li, Chien-pu, and 李建溥. "Effects of Alloying Elements on the Wear Resistance of SK85 High-Carbon Tool Steel." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/fmu6nz.

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碩士 國立高雄第一科技大學 機械與自動化工程所 96 Due to high hardness and wear resistance, high carbon tool steel is widely applied in woodworking tools. High carbon tool steel with poor hardenability can not achieve good microstructure and wear resistance through the oil quenching process. Although high carbon steel can be well hardened by water quenching, dimensional change and quenching cracking are concerned. The hardenability of high carbon steel can be approved by the addition of molybdenum and chromium. With alloying elements addition higher martensite percentage and good wear resistance can be obtained. In this study wear resistance of SK85, SK85+0.15wt%Cr, SK85+0.25wt%Cr, SK85+0.15wt%Cr+0.20wt%Mo, SK85+ 0.20wt%Mo, and SK85+0.40wt%Mo are analyzed. The aims of this study are (1) to establish the heat-treatment parameters for quenching and tempering processes, (2) to analyze the effects of Cr and Mo on the wear resistance (3) to observe the size and distribution of carbide by TEM and X-ray (4) to establish the wear mechanis.

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47

Elger, Ragna. "High temperature corrosion in biomass-fired energy applications : Alloying effects and test environment comparisons." Doctoral thesis, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-186318.

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To reduce the greenhouse effect, the use of renewable fuel has to be increased. As renewable fuel has different characteristics compared to fossil fuel regarding content of trace metals, alkali, chlorine and sulphur, the corrosion characteristics in high temperature energy processes have to be evaluated. This thesis concerns high temperature corrosion in the superheater region of a boiler and the syngas cooler area of a gasifier. For the superheater region, laboratory exposures were performed. The methods included a salt dip exposure, where samples were dipped in an equimolar solution of ZnCl2 and KCl, and two salt bed exposures with different chlorine concentrations, 10 and 20 wt%. Ranking of the materials showed that a Ni content above 10 wt% and Cr above 20 wt% reduced corrosion rates in the salt dip and in the 10% Cl salt bed exposure. For exposure in the 20% Cl bed, even higher alloying was needed. An alumina forming austenitic steel showed future potential in sulphidising-chlorinating environments. For the gasifier region, the effect of HCl in a simulated gasifier atmosphere was studied and also samples exposed in the syngas section of a biomass gasifier were investigated. Metal loss was low for all exposures and it was observed that chlorine had minor influence. For the plant exposed samples, a difference compared to that reported for coal gasifiers was the absence of FeS for the lowest alloyed steel. Instead, a deposit with pronounced content of Zn, Ca, S and O was present on the surface. Zinc was suggested to mitigate corrosion. Thermodynamic modelling was used to explain phases present and to predict the nitridation behaviour of an alumina forming austenitic steel. Equilibrium and kinetic modelling of the nitridation showed good coherence with the observed microstructures. However, the kinetic modelling resulted in larger nitridation depths than observed experimentally which was attributed to the presence of a thin oxide layer on the surface of the samples. QC 20160510

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Hu, Long-Yu, and 胡隆羽. "The Relationship Between Alloying Elements and the Amount of Retained Austenite in SUS420 Stainless Steel Welds." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/14462185843363078590.

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Chou, Shao-Cheng, and 周紹誠. "The effect of heat treatment on the mechanical properties of a steel alloying with Mn element." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/qt9eve.

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碩士 國立中山大學 材料與光電科學學系研究所 102 The purpose of this study is to develop third generation advanced high strength steel alloyed with medium Mn content. In this study, the steel alloying with Mn element were processed by cold rolling combined with heat treatment to control the microstructure and the stabilization of austenite. The microstructure obtained consisted of ferrite, austenite, and carbide after 700oC heat treatment. The austenite obtained can be stabilized at room temperature. The steel exhibits high tensile strength and high elongation, which attribute to the occurrence of the strain-induced martensite phase transformation which can significantly increase the work-hardening rate and postpone necking during deformation.

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Tsai, Yi-yung, and 蔡益元. "The Effects of Alloying Elements on Wear Resistance Performance in Medium Carbon Steel Cladded with Ceramics Powder." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/51598909612998582785.

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碩士 國立臺灣科技大學 機械工程系 88 This thesis investigated the medium carbon wear resistance, which improved by WC and TiC powders cladding with gas tungsten arc welding (GTAW) method. Various metal powder with different percentage were added to the based powder to prepare the cladding powder, which were used to study the influence of various metal powder effect on cladded surface wear resistance ability. Then, rotating type tribometer was used to evaluate the wear behaviors of the different caldded specimens under dry sliding conditions. Optical microscope and scanning microscope (SEM) were used to identify the microstructure and wear mechanism. It also, however, EPMA used to analysis the compositions of second phases in cladded region. According the results, the specimen clad by WC based powder contains certain Ti metal powder, had the best wear resistance performance in all specimens. However, in low sliding speed, the TiC based powder contains certain W powder cladding specimen had the better wear resistance performance; on the other hand, in high sliding speed the TiC based powder contain Cr powder cladding specimen had the better wear resistance performance. In addition, oxidation wear always occurs in high sliding speed condition such that the wear rate reduced compare with low sliding speed condition.

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Dissertations / Theses on the topic 'Steel alloying'

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