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Thermal analysis of the chip formation in austenitic stainless steel

Chagas, G M P; Barbosa, Adilson Macedo Hampe; Carvalho, Alberto Barbosa de; Machado, Izabel Fernanda
Fonte: Amsterdam Publicador: Amsterdam
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.56%
The most important property of austenitic stainless steels is corrosion resistance. In these steels, the transition between paramagnetic and ferromagnetic conditions occurs at low temperatures. Therefore, the use of austenitic stainless steels in conditions in which ferromagnetism absence is important can be considered. On the other hand, the formation of strain-induced martensite is detected when austenitic stainless steels are deformed as well as machined. The strain-induced martensite formed especially in the machining process is not uniform through the chip and its formation can also be related to the Md temperature. Therefore, both the temperature distribution and the gradient during the cutting and chip formation are important to identify regions in which martensite formation is propitiated. The main objective here is evaluate the strain-induced martensite formation throughout machining by observing microstructural features and comparing these to thermal results obtained through finite element method analysis. Results show that thermal analysis can give support to the martensite identified in the microstructural analysis.; 14th CIRP Conference on Modeling of Machining Operations (CIRP CMMO)

Characterization of a new Fe-C-Mn-Si-Cr bearing alloy: tempered martensite embrittlement susceptibility

Marcomini, José Benedito; Goldenstein, Helio
Fonte: New York Publicador: New York
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.37%
Bearing steels containing 1% C and 1.5% Cr have been the usual material of choice for machine components submitted to rolling and contact fatigue, for more than a century. As a rule these steels are quenched from the intercritical gamma + carbide region and tempered at low temperatures (less than 250 °C), in order to retain the high hardness of the martensite matrix and avoid the tempered martensite embrittlement (TME) phenomena, which compromise the toughness of steels tempered at higher temperatures. A new high Si alloy was developed for bearing applications. The inhibiting and/or retarding effect of Si on the kinetics of cementite precipitation leads to a higher temperature of TME occurrence, allowing the tempering of the components at a higher temperature, thus increasing the toughness, without sacrificing the high hardness. The purpose of this work was to confirm the TME resistance of the new alloy. In this work, impact tests result for commercial SAE/AISI 52100 (0.25% Si) and for a modified 52100 containing 1.74% Si, were compared. No evidence of TME was detected on the Si-modified steel.; CNPq

Caracterização da nova liga Fe-C-Mn-Si-Cr: fragilização da martensita revenida e curvas de revenimento.; A new Fe-C-Mn-Si-Cr alloy characterization: tempered martensite embrittlement and tempering curves.

Marcomini, José Benedito
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/03/2012 PT
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O aço SAE/AISI 52100 é utilizado para a fabricação de rolamentos como também na fabricação de outras peças e dispositivos como cames de eixo comando de válvulas. Um dos problemas desta liga é a necessidade de revenimentos em temperaturas muito baixas para obtenção de alta dureza e para evitar o fenômeno da fragilização da martensita revenida (FMR), em detrimento da tenacidade. Foi projetada uma nova liga Fe-C-Mn-Si-Cr (AISI/SAE 52100 modificado com 1,74% de Si e 0,96% de Mn) baseada na mesma ideia do aço 300M em relação ao SAE/AISI 4340. O efeito do Si na cinética de precipitação da cementita retarda a fragilização da martensita revenida (FMR), além de aumentar a dureza e mantê-la com valores relativamente altos mesmo quando do revenimento em temperaturas mais altas. A proposta do presente trabalho foi comprovar a resistência desta nova liga frente à FMR e demonstrar a resistência ao amolecimento perante o revenimento (curvas de revenimento). Com o intuito de estudar o efeito do Si na dureza do novo aço, foram elaboradas curvas de revenimento medindo-se essa propriedade em amostras do novo aço e do aço comercial após têmpera em temperaturas de austenitização na faixa de 825ºC e 960ºC, seguida por tratamento criogênico em nitrogênio líquido (-196ºC) durante doze horas e revenidas em temperaturas na faixa de 250ºC a 500ºC. Foram obtidas durezas acima de 60HRC...

Efeitos da temperatura de laminação na formação e na reversão de martensita induzida por deformação no aço inoxidável austenítico AISI 304L.; Effects of the rolling temperature on the formation and on the reversion of strain induced martensite in a AISI 304L stainless steel.

Gomes, Tiago Evangelista
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/02/2012 PT
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37.72%
Objetivo principal desta dissertação foi verificar os efeitos da temperatura de laminação na formação de martensita induzida por deformação e na sua posterior reversão da martensita para austenita no aço inoxidável austenítico AISI 304L. O estudo foi predominantemente microestrutural e para análise e caracterização foram utilizadas as técnicas de microscopia óptica, microscopia eletrônica de varredura, difração de raios X, medidas de dureza Vickers e medidas de fases ferromagnéticas por ferritoscopia. As amostras foram inicialmente solubilizadas a 1100 ºC por uma hora, visando a dissolução de uma pequena quantidade residual de ferrita encontrada nas amostras na condição como recebida, depois laminadas em diferentes temperaturas, determinando-se curvas de endurecimento por deformação e de formação de martensita induzida por deformação em função do grau de deformação. Em seguida, foram realizados pré-recozimentos a 600 ºC, favorecendo apenas a reversão da martensita para austenita, de maneira que não ocorresse a recristalização. A quantidade e a temperatura de deformação apresentaram forte influência na quantidade de martensita formada, no endurecimento por deformação e na cinética de amolecimento durante o recozimento. Os pré-tratamentos realizados a 600 ºC causaram acentuada reversão da martensita...

Estudo da formação e reversão de martensita induzida por deformação na austenita de dois aços inoxidáveis dúplex.; The study of formation and reversion of the strain induced alpha-prime martensite in duplex and super duplex stainless steels

Aguiar, Denilson José Marcolino de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/08/2012 PT
Relevância na Pesquisa
37.63%
No presente trabalho foram estudados os fenômenos de encruamento e, principalmente, a formação e reversão da martensita alfa-linha (a', cúbica de corpo centrado, CCC, ferromagnética) induzida por deformação em um aço inoxidável dúplex UNS S31803 e um super dúplex UNS S32520. Inicialmente, as microestruturas dos dois materiais na condição solubilizada foram caracterizadas com auxílio de várias técnicas complementares de análise microestrutural. Foram determinadas fração volumétrica, estrutura cristalina, composição química, tamanho e morfologia das duas fases (ferrita e austenita). Posteriormente, os dois aços foram deformados por dois métodos: a laminação a frio, dividida em vários estágios, com menores graus de deformação e a limagem, sendo que o cavaco limado resultante apresenta altos graus de deformação. Algumas amostras deformadas foram recozidas. Os fenômenos de encruamento, formação e reversão de martensita induzida por deformação na austenita, recuperação, recristalização da austenita e da ferrita no cavaco limado foram estudados predominantemente por difratometria de raios X e usando o método de Rietveld. A difratometria de raios X também foi utilizada para determinação das microdeformações residuais e tamanhos de cristalito (subgrão)...

Martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys

Adorno, A. T.; Silva, R. A G
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1087-1093
ENG
Relevância na Pesquisa
37.48%
The martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys was studied using microhardness measurements, classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and in-situ high-temperature X-ray diffractometry (XRD). The results for the Cu-10%Al alloy indicated a process dominated by the martensite ordering assisted by migration of quenched-in vacancies and followed by the consumption of the α phase. For the Cu-10%Al-10%Ag alloy the dominant process is the consumption of the α phase associated with a decrease in the ordering degree of the martensitic phase. © 2007 Springer Science+Business Media, LLC.

Formation and reversion of strain induced martensite on Fe-Cr-Ni alloys

Brollo,Gabriela Lujan; Mei,Paulo Roberto
Fonte: Escola de Minas Publicador: Escola de Minas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2013 EN
Relevância na Pesquisa
37.56%
Austenitic stainless steels represent a significant portion of the alloys used in the aeronautical, chemical, shipbuilding, food processing and biomechanical industries. They combine good mechanical properties with high corrosion resistance. When subjected to cold deformation, these steels exhibit a metastable phase called: strain induced martensite (ferromagnetic), whose formation increases mechanical strength and formability, allowing for a wide range of applications. Heated from room temperature, the strain induced martensite transforms to austenite (non-magnetic). It is easy to find information in literature about the strain induced martensite for 18Cr/8Ni austenitic steels, but there is no data for high nickel alloys like A286 (26Ni, 15Cr), Incoloy 800 (30-40 Ni, 21Cr) and Inconel (50Ni, 19Cr). Therefore, this study aimed to verify the formation of strain induced martensite after cold working in Fe-18Cr base alloys with the addition of up to 60 %Ni. The reversion of this phase to austenite after annealing up to 600 ºC was also studied. Optical microscopy, magnetic characterization tests, and x-ray diffraction were used to analyze the transformations.

Deformation induced martensite in an AISI 301LN stainless steel: characterization and influence on pitting corrosion resistance

Abreu,Hamilton Ferreira Gomes de; Carvalho,Sheyla Santana de; Lima Neto,Pedro de; Santos,Ricardo Pires dos; Freire,Válder Nogueira; Silva,Paulo Maria de Oliveira; Tavares,Sérgio Souto Maior
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2007 EN
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37.68%
In austenitic stainless steels, plastic deformation can induce martensite formation. The induced martensite is related to the austenite (gamma) instability at temperatures close or below room temperature. The metastability of austenite stainless steels increases with the decreasing of stacking fault energy (SFE). In this work, the deformation induced martensite was analyzed by X ray diffraction, electron back scatter diffraction (EBSD), magnetic methods and atomic force microscope (AFM) in samples of a low SFE austenitic stainless steel, AISI 301LN and compared with a medium SFE stainless steel, AISI 316L. Both techniques, X ray diffraction and EBSD, presented similar quantities for the alpha’-martensite. Texture results indicate that the crystallographic orientation of the formed alpha’-martensite is {001}<110> and {103}<110>. The morphology of alpha’-martensite was analyzed by AFM. Corrosion tests showed that deformation reduces pitting corrosion and generalized corrosion resistance in both steels.

Formal analysis of isothermal martensite spread

Rios,Paulo Rangel; Guimarães,José Roberto Costa
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 EN
Relevância na Pesquisa
27.63%
A formal kinetic approach was applied to the spread of isothermal martensite over the neighboring austenite grains in a Fe-23.2 wt. (%) Ni-2.8 wt. (%) Mn alloy. The number of grains in a spread event changed with parent austenite grain size. However, isothermal martensite spread formed from fine-grained parent austenite and athermal martensite from a Fe-31 wt. (%) Ni-0.02 wt. (%) C alloy studied in a previous work followed the same microstructural path. The number of grains per spread- event found in the present study was shown to be consistent with the number of neighbors of the grain originating the spread event by means of a simple geometrical model of the parent austenite grain network. The study of the kinetics of isothermal martensite spread showed that the nucleation rate of the spread-event in isothermal martensite remained constant during the transformation. This result parallels the constant nucleation rate of the spread-event also found using the same methodology in athermal martensite formed in a Fe-31 wt. (%) Ni-0.02 wt. (%) C alloy studied in a previous work.

Quantitative interpretation of martensite microstructure

Guimarães,José Roberto Costa; Rios,Paulo Rangel
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2011 EN
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This work reviews issues and advances a formalism for quantitative interpretation of martensite microstructure, heeding the influence of transformation uniformity and the interaction of martensite with its surroundings. The relationship of volume fraction and number density of martensite units required for kinetics analysis is derived. Additionally we apply the new model to obtain the microstructural path function (MPF) of martensite, and to analyze the autocatalytic spread of the transformation during the martensite burst in Fe-31 wt. (%) Ni-0.02 wt. (%) C. The growth of an autocatalytic spread event relates to the chemical driving force, whereas the number of such events relates to the probability of finding a nucleation site to initiate the reaction.

Effect of initial microstructures on the properties of Ferrite-Martensite Dual-Phase pipeline steels with Strain-Based design

Hu,Yueyue; Zuo,Xiurong; Li,Rutao; Zhang,Zhanzhan
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2012 EN
Relevância na Pesquisa
37.68%
This study aims to investigate the effect of initial microstructures on the properties of ferrite-martensite dual-phase pipeline steels with strain-based design. For this purpose, the as-received acicular ferrite steels were first austenitized at 920 ºC for 15 minutes followed by air cooling and water quenching to produce ferrite-pearlite and ferrite-martensite microstructure, respectively. Subsequently, the steels with ferrite-pearlite, ferrite-martensite and as-received acicular ferrite microstructure were intercritically annealed at 820 ºC for 10 minutes followed by water quenching to produce three different ferrite-martensite dual-phase microstructures. Tensile tests, Vickers hardness and Charpy impact tests were carried out to investigate the mechanical properties. Scanning electron microscope was used to analyze the microstructures and tensile fractographs. The results showed that all the tensile specimens of these three different ferrite-martensite dual-phase steels fractured in ductile mode, however, their microstructures and mechanical properties varied significantly. By contrast, the ferrite-martensite dual-phase steel derived from acicular ferrite initial microstructure had optimal combination of the strength, toughness and deformability...

The martensite transformation in Ni-based coatings & bulk alloys

Clancy, Marie
Fonte: University of Limerick Publicador: University of Limerick
Tipo: info:eu-repo/semantics/doctoralThesis; ul_published_reviewed; ul_theses_dissertations
ENG
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peer-reviewed; This thesis examines the formation of martensite in Ni-based super-alloys in both an alloy-coating system and in the bulk alloy, NiPtAl. The alloy-coating study was designed to test the hypothesis that an extra layer of Ni could favourably alter diffusion gradients within the alloy-coating system in order to preferentially promote martensite(ß ’) formation. Such martensite formation would have the advantage of delaying the development of y’-Ni3Al, and reducing precipitation of the brittle topologically close packed phases, on subsequent heat-treatment. The work was a success in that deposition of a layer of Ni on the alloy, prior to aluminising did alter the diffusion profile of the coating-alloy system. During the aluminising process, a layer of very Ni-rich y’ formed at the coating/alloy interface. As the diffusivity of elements through this phase is notably lower than that of elements diffusing through the Al-rich ß -NiAl phase, the coating produced was thinner and had a higher Al content. These effects resulted in a coating that retained a ß +ß ’ majority composition for a longer period of oxidation, than its un-plated equivalent. As the molar volume change of the ß - ß ’ transformation is less than that of ß - y’...

Microstructural Path Analysis of Martensite Dimensions in FeNiC and FeC Alloys

Guimarães,José Roberto Costa; Rios,Paulo Rangel
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2015 EN
Relevância na Pesquisa
27.78%
The properties of steels that undergo martensite transformation after or during processing depend on characteristics and arrangement of martensite units within the microstructure. In this work, the global microstructure descriptors of martensite transformation are related to the individual dimensions of the martensite units, the "intrinsic dimensions", – radius, thickness and aspect ratio – compensated for interactions among those units. In other words, the dimensions a martensite unit would have if it grew without impingement. This is accomplished by means of the microstructural path method. The methodology was applied to experimental data of martensite transformation in FeNiC and FeC alloys. The analysis of martensite dimensions permitted observing that the microstructural path of martensite includes a thermally activated step. We conclude that this thermally activated step does not mean that martensite itself has thermally activated growth step but that arrest of the martensite thickening process, owing to dislocation interaction with the interface motion may be thermally activated.

Effect of cooling rate on (ε, α') martensite formation in twinning/transformation-induced plasticity Fe-17Mn-0.06C steel

Dafé,Sara Silva Ferreira de; Sicupira,Felipe Lucas; Matos,Flávia Cristina Silva; Cruz,Naiara Silva; Moreira,Débora Rezende; Santos,Dagoberto Brandão
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
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The cooling rate, density of stacking faults, austenite grain size, and temperature strongly influence the γfcc → εhcp → a'bcc martensite transformation in austenitic alloys. During cooling, austenitic Fe-Mn steels can partially transform to ε and α'martensites within a restricted chemical composition. Martensite formation will influence the mechanical behavior of the alloy. The microstructure evolution under three cooling rates of a hot-rolled austenitic steel, Fe-17.0Mn-0.06C (wt%), was analyzed by optical microscopy and scanning electron microscopy/electron backscatter diffraction. The volume fraction of martensite and austenite were measured by X-ray diffraction line profile analysis by directly comparing the as-cast alloy, alloy subjected to different cooling conditions, and this processed with hot rolling.

Texture analysis of deformation induced martensite in an AISI 301L stainless steel: microtexture and macrotexture aspects

Abreu,Hamilton Ferreira Gomes de; Silva,Marcelo José Gomes da; Herculano,Luís Flávio Gaspar; Bhadeshia,Harry
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2009 EN
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Experiments have been conducted to study the strain induced transformation from austenite to martensite in a metastable AISI 301LN austenitic stainless steel, deformed by uniaxial tension applied along rolling direction. Samples deformed 10 and 20% have shown the presence of α´ martensite phase. Measured pole figures of martensite phase were compared to calculated ones, assuming no variant selection and selection of variants where interaction between stress and the plate of martensite adds to the driving force transformation variants. EBSD (electron back scatter diffraction) microtexture experiments and macrotexture X-ray diffraction were performed. The orientation distribution functions (ODFs) from measured pole figure data were calculated. The measured results were compared with calculated results in both polycrystalline and single crystal samples of austenite. The results showed that the calculated textures based in a process of variant selection consistent with Patel and Cohen's theory, which emphasizes a mechanical component of free energy, were in good agreement with measured texture.

Role of stress-assisted martensite in the design of strong ultrafine-grained duplex steels

Yen, Hung-Wei; Ooi, Steve Woei; Eizadjou, Mehdi; Breen, Andrew; Huang, Ching-Yuan; Bhadeshia, H. K. D. H.; Ringer, Simon P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.56%
This work explains the occurrence of transformation-induced plasticity via stress-assisted martensite, when designing ultrafine-grained duplex steels. It is found that, when the austenite is reduced to a fine scale of about 300 nm, the initial deformation-induced microstructure can be dominated by parallel lamellae of epsilon martensite or mechanical twinning, which cannot efficiently provide nucleation sites for strain-induced martensite. Hence, alpha martensite nucleation occurs independently by a stress-assisted process that enhances transformation-induced plasticity in ultrafine-grained austenite. This metallurgical principle was validated experimentally by using a combination of transmission Kikuchi diffraction mapping, transmission electron microscopy, and atom probe microscopy, and demonstrated theoretically by the thermodynamics model of stress-assisted martensite.; Comment: We've updated a correct manuscript

Residual stress induced stabilization of martensite phase and its effect on the magneto-structural transition in Mn rich Ni-Mn-In/Ga magnetic shape memory alloys

Singh, Sanjay; Kushwaha, Pallavi; Sceibel, F.; Liermann, Hanns-Peter; Barman, S. R.; Acet, M.; Felser, C.; Pandey, Dhananjai
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/05/2015
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27.63%
The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magneto-structural transition that is accompanied with a steep drop in magnetization (i.e., 'delta M') around the martensite start temperature (Ms) due to the lower magnetization of the martensite phase. In this communication, we show that 'delta M' around Ms in Mn rich Ni-Mn based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above the Ms and the austenite finish (Af) temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder diffraction patterns reveals stabilized martensite phase fractions as 97, 75 and 90% with corresponding residual microstrains as 5.4, 5.6 and 3% in crushed powders of the three different Mn rich Ni-Mn alloys, namely, Mn1.8Ni1.8In0.4, Mn1.75Ni1.25Ga and Mn1.9Ni1.1Ga, respectively. Even after annealing at 773 K, the residual stress stabilised martensite phase does not fully revert to the equilibrium cubic austenite phase as the magneto-structural transition is only partially restored with reduced value of 'delta M'. Our results have very significant bearing on application of such alloys as inverse magnetocaloric and barocaloric materials.

Design and modelling of ultra-high strength steels: nanoprecipitation and plasticity

Kim, Bij-Na
Fonte: University of Cambridge; Department of Materials Science and Metallurgy; Lucy Cavendish College Publicador: University of Cambridge; Department of Materials Science and Metallurgy; Lucy Cavendish College
Tipo: Thesis; doctoral; PhD
EN
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27.63%
Understanding the changes occurring in the mechanical properties during martensite tempering is essential in the development of new industrial grades. The aim of this research was to develop new ultra-high strength steels via nanoprecipitation control, which requires an understanding of the processing-microstructure-property relationship in medium carbon (0.5-0.6 wt.%) steels throughout tempering. Much of the work has been centred in understanding the role of silicon at the precipitation level and in the recovery of martensite. By using an existing spring steel grade, the effect of interrupted ageing (IA) in tempered martensite has been studied. In IA, an intermediate step between quenching and tempering is introduced, where quenched martensite is left to rest at room temperature for a defined period of time. By allowing carbon segregation into dislocation cores, the incorporation of IA resulted in a more stable microstructure and hardness improvement. The effect of silicon in the epsilon to cementite carbide transition has also been studied. The classical nucleation theory was applied in order to model cementite formation under paraequilibrium conditions, thus incorporating silicon during nucleation. Characterisation using high energy X-rays showed the inhibiting effect of silicon in the overall cementite precipitation. The second effect of silicon was observed in the martensite recovery. A series of experiments were carried out in order to capture the various microstructural changes taking place during tempering: precipitation...

Combining bainite and martensite in steel microstructures for light weight applications

Santofimia,M.J.; van Bohemen,S.M.C.; Sietsma,J.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2013 EN
Relevância na Pesquisa
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Multiphase microstructures in steel have been intensively studied in the past years, but combining non-equilibrium phases still offers a great potential for further development of these steel grades. Thus, improved combinations of mechanical properties can be obtained with microstructures formed by bainite or martensite, in combination with retained austenite. In particular, microstructures on the basis of carbon-depleted martensite and retained austenite can be produced by the very promising production process named quenching and partitioning (Q&P). Originally, the Q&P process aimed to avoid the formation of bainite during the heat treatment. However, the process does provide the possibility for (carbide-free) bainite formation during the partitioning step, i.e. in the presence of martensite. This article evaluates this approach, considering that the formation of bainite from austenite is strongly influenced by the preceding formation of martensite. Although the accelerating effect of the presence of martensite during bainite formation has been observed, it is not yet fully understood, and experimental and theoretical studies are being performed in order to come to a more effective exploitation of these processes for the formation of multiphase microstructures.

Surface martensite white layer produced by adhesive sliding wear-friction in aisi 1065 steel

Sipos,Konstantin; López,Marta; Trucco,Mauricio
Fonte: Universidad Simón Bolívar; ; Publicador: Universidad Simón Bolívar; ;
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2008 EN
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37.37%
White layers (WLs) produced in hard steels by adhesive sliding wear without lubricants  have been characterized using microindentation, optical microscopy, scanning electron microscopy (SEM) and chemical analysis through energy dispersive spectroscopy (EDS). The WL is found to have a hardness of values ranging between 825 to 916 HV and ultrafine grained structure with layer size ranged around 50 μm. These two characteristics of white layers distinguish it from martensite structure formed in steels by heat treatment. The formation of this untempered martensite with ultrafine structure is based on a large strain deformation and stress at elevated temperature states that promote conditions of severe wear by friction.