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Showing papers on "Austenite published in 2006"


Journal ArticleDOI
TL;DR: The morphology and crystallography of lath martensite in two Mn-containing interstitial free steels and a maraging steel were examined in detail by a combination of transmission electron microscopy, electron backscatter diffraction in a scanning electron microscope and optical microscopy.

641 citations


Journal ArticleDOI
TL;DR: In this paper, a novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described, which can be used to generate microstructures with martensites/austenite combinations giving attractive properties.
Abstract: A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.

618 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructure and the strength of lath martensite in Fe 0.2C and Fe 1.2Mn alloys were analyzed as a function of the prior austenite grain size.
Abstract: The microstructure and the strength of the lath martensite in Fe–0.2C and Fe–0.2C–2Mn alloys were analyzed as a function of the prior austenite grain size. The size of martensite packets formed within individual austenite grains was controlled by the austenite grain size but not affected by the Mn addition. However, the further subdivision of packets into blocks differed significantly in the two alloys, and at a given austenite grain size a smaller block size was observed in the Mn containing alloy. The yield strength of the two alloys was related to the packet size and the block size, respectively, and the results suggested that the block size is the key structural parameter when analyzing the strength–structure relationship of lath martensite in low carbon steels.

496 citations


Reference BookDOI
28 Sep 2006
TL;DR: In this article, the authors discuss the effects of Alloying elements on the heat treatment of steel and present a classification and mechanism of steel transformation, which is based on the Liscic' Heat Treatment with Gaseous Atmospheres.
Abstract: Revised! Steel Nomenclature A. Kumar Sinha, C. Wu, and G. Liu New! Classification and Mechanisms of Steel Transformation S.S. Babu Fundamental Concepts in Steel Heat Treatment A.V. Sverdlin and A.R. Ness Effects of Alloying Elements on the Heat Treatment of Steel A.V. Sverdlin and A.R. Ness Hardenability B. Liscic' Steel Heat Treatment B. Liscic' Revised! Heat Treatment with Gaseous Atmospheres J. Grosch Revised! Nitriding Techniques, Ferritic Nitrocarburizing, Austenitic Nitrocarburizing Techniques and Methods D. Pye Quenching and Quenching Technology H.M. Tensi, A. Stich, and G.E. Totten New! Distortion of Heat-Treated Components G.E. Totten and M. Narazaki New! Tool Steels E. Essadiqi and G.E. Totten New! Stainless Steel Heat Treatment A.F. Padilha, R.L. Plaut, and R.R. Rios New! Heat Treatment of Powder Metallurgy Steel Components J.W. Newkirk and S.N. Thakur APPENDICES Common Conversion Constants Temperature Conversion Table Volume Conversion Table Hardness Conversion Tables: Hardened Steel and Hard Alloys Recommended MIL 6875 Specification Steel Heat Treatment Conditions Colors of Hardening and Tempering Heats Weight Tables For Steel Bars Round and Square Bars, Specific Gravity 7.85 Index

317 citations


Journal ArticleDOI
M. Michiuchi1, Hiroyuki Kokawa1, Zhi Wang1, Yutaka S. Sato1, K. Sakai1 
TL;DR: In this article, twin-induced grain boundary engineering utilizing optimized one-step thermomechanical processing with 3% pre-strain and subsequent annealing at 1240 K for 72h was introduced into type 316 austenitic stainless steel.

251 citations


Journal ArticleDOI
TL;DR: In this article, a unique martensitic transition from the ferromagnetic austenite phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced reverse transition was confirmed in a high magnetic field.
Abstract: Magnetic and martensitic transition behaviors of a Ni46Mn41In13 Heusler alloy were investigated by differential scanning calorimetry and vibrating sample magnetometry. A unique martensitic transition from the ferromagnetic austenite phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced “reverse” transition was confirmed in a high magnetic field. In addition, a large positive magnetic entropy change, which reached 13J∕kgK at 9T, was observed to accompany reverse martensitic transition. This alloy shows promise as a metamagnetic shape memory alloy with magnetic-field-induced shape memory effect and as a magnetocaloric material.

244 citations


Journal ArticleDOI
TL;DR: In this article, the stacking fault energy of austenitic stainless steels has been determined using a quantum mechanical first-principles approach, identifying the electronic, magnetic and volume effects responsible for the compositional dependence of the SFE.

210 citations


Journal ArticleDOI
TL;DR: In this paper, a theory for the mechanical stabilisation of plastically deformed austenite by balancing the force which drives the transformation interface against the resistance from dislocation debris in the Austenite was developed.
Abstract: A theory has been developed for the mechanical stabilisation of plastically deformed austenite by balancing the force which drives the transformation interface against the resistance from dislocation debris in the austenite. The work has been used to explain why very large strains are required to mechanically stabilise certain stainless steels, and also to interpret the subunit mechanism of bainite growth.

209 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of isothermal treatment at 750 °C on the microstructure of duplex stainless steels has been investigated, and the qualitative and quantitative analysis of precipitations nucleated after aging was carried out, where two kinds of Cr- and Mo-enriched intermetallic phases, σ and χ, were found to precipitate preferentially at ferrite-austenite interface and within the ferrite phase.

192 citations


Journal ArticleDOI
TL;DR: Arcelor Research, in conjunction with TKS, has recently developed an ultra high strength Fe-Mn-C austenitic steel with excellent formability for automotive applications.
Abstract: The current strong demand for vehicle lightening from the automobile sector requires flat carbon steel manufacturers to develop new advanced grades capable of fulfilling the increasingly stringent technical requirements of this market. Two basic approaches are possible: - short term strategies for incremental improvements in the mechanical properties of existing products which can then be produced in thinner gauge strips with equivalent functional properties, - longer term solutions involving the development of breakthrough products such as ultra high strength ductile austenitic steels or low-density steels alloyed with light elements (Al, Mg, Si). Arcelor is actively pursuing both these avenues of research. Restricting the discussion to the second point, it is clear that there are many technical hurdles and conflicting requirements to be overcome in order to produce a marketable product. Arcelor Research, in conjunction with TKS, has recently developed an ultra high strength Fe-Mn-C austenitic steel with excellent formability for automotive applications. The X-IP TM 1000 steel composition is optimised to provide the best compromise in ultimate tensile strength (>1000 MPa) and total elongation (>50%) at room temperature. These properties are achieved through the optimisation of the TWIP (TWinning Induced Plasticity) effect by careful control of the stacking fault energy (SFE) and the final microstructure. The austenite matrix is fine grained (grain size <10 µm for hot strips and <3 µm for cold strips), contains little or no cementite and is exempt from martensitic transformations under cold working. The steel can be processed on conventional industrial lines (continuous casting, hot and cold rolling and continuous annealing) in a wide range of formats. In this paper we present the factors that determine the choice of composition (phase stability diagrams and SFE modelling) and we describe the evolution of the microstructure at different stages in the production process. The relationship between the microstructure and the final mechanical properties is discussed. X-IP

184 citations


Journal ArticleDOI
TL;DR: In this paper, high-resolution transmission electron microscopy and three-dimensional atom probe observations show that a reverse transformation of body-centred cubic ferrite to face-centered cubic austenite occurs during severe plastic deformation of a pearlitic steel resulting in a nanocrystalline structure.

Journal ArticleDOI
TL;DR: In this paper, the solubility of nitrogen in austenitic stainless steel was investigated thermogravimetrically by equilibrating thin foils of AISI 304 in ammonia/hydrogen gas mixtures.
Abstract: The solubility of nitrogen in austenitic stainless steel was investigated thermogravimetrically by equilibrating thin foils of AISI 304 and AISI 316 in ammonia/hydrogen gas mixtures. Controlled dissolution of colossal amounts of nitrogen under metastable equilibrium conditions was realized, with nitrogen contents as high as corresponding to an occupancy of y N=0.61 of the interstitial sublattice, i.e., about 38 at. pct N. Associated with the dissolution of these unprecedented nitrogen contents in an austenitic matrix a reversible volume expansion of the austenite lattice occurred for y N > 0.17. A simplistic model based on a statistical distribution fo the nitride forming elements over the octahedrons constituting the solid state agrees favorably with the experimental data.

Journal ArticleDOI
TL;DR: In this article, the stability and rate of transformation of the austenite particles in low-alloy multiphase transformation-induced-plasticity (TRIP) steels have been investigated experimentally, with special attention paid to the effect of the chemical composition, the temperature, and the size of the particles.
Abstract: Low-alloy multiphase transformation-induced-plasticity (TRIP) steels offer excellent mechanical properties in terms of elongation and strength. This results from the complex synergy between the different phases, i.e., ferrite, bainite, and retained austenite. The precise knowledge of the austenite-to-martensite transformation kinetics is required to understand the behavior of TRIP steels in a wide array of applications. The parameters determining the stability of the metastable austenite were reviewed and investigated experimentally, with special attention paid to the effect of the chemical composition, the temperature, and the size of the austenite particles. The results show that the stability and rate of transformation of the austenite particles in TRIP steels have a pronounced composition dependence: austenite particles transform at a faster rate in CMnSi TRIP steel than in TRIP steels in which Si is fully or partially replaced by Al and P. The results clearly support the view that (1) both a high C content and a submicron size are required for the room-temperature stability of the austenite particles and (2) the effect of the chemical composition on the transformation is due to its influence on the intrinsic stacking-fault energy. In addition, the composition dependence of the Md 30 temperature was derived by regression analysis of experimental data. The influence of the size of the retained austenite particles on their Ms σ temperature was studied by means of a thermodynamic model. Both the analysis of the transformation-kinetics data and the microstructural analysis by transmission electron microscopy revealed the very limited role of autocatalysis in the transformation.

Journal ArticleDOI
TL;DR: In this article, the sigma phase precipitation of three stainless steels: austenitic type 316L (17Cr−12Ni−2·5Mo, wt-%), superferritic type DIN W. Nr. 1·4575 (Nb−28Cr−4Ni-2Mo, Wt-%) and duplex type Din W.Nr.1·4462 or UNS S31803 (22Cr−5·5Ni-3Mo-0·14N, wT-%).
Abstract: The present work studies, in a comparative manner, the sigma phase precipitation of three stainless steels: austenitic type 316L (17Cr–12Ni–2·5Mo, wt-%), superferritic type DIN W. Nr. 1·4575 (Nb–28Cr–4Ni–2Mo, wt-%) and duplex type DIN W. Nr. 1·4462 or UNS S31803 (22Cr–5·5Ni–3Mo–0·14N, wt-%). In austenitic stainless steel, the formation of sigma phase occurred both at austenite grain boundaries and inside delta ferrite islands. In superferritic stainless steel, sigma phase occurred both at grain boundaries and in the grain interior. In the ferrites, both in the duplex and in the austenitic steel, sigma phase formation occurred by eutectoid reaction ferrite→sigma + austenite. The tendency towards precipitation of the sigma phase in the three types of steel investigated can be placed in the following sequence: duplex>superferritic>austenitic.

Journal ArticleDOI
TL;DR: In this paper, the Mecking-Kocks theory was used for the simulations of the stress-strain curves of the separate phases of a multiphase transformation-induced plasticity (TRIP) steel.

Journal ArticleDOI
TL;DR: In this article, the electronic structures of both cubic austenite and tetragonal martensite Mn2NiGa were calculated by self-consistent full-potential linearized-augmented plane-wave (FP-LAPW) method.
Abstract: Both experimental and theoretical studies have been carried out to study the structure and magnetic properties of Mn2NiGa alloys. We have found, instead of forming L2(1) structure where both A and C sites are occupied by Mn atoms, the alloy favor a structure where the C site is occupied by Ni atoms and Mn atoms at A and B sites. The electronic structures of both cubic austenite and tetragonal martensite Mn2NiGa were calculated by self-consistent full-potential linearized-augmented plane-wave (FP-LAPW) method. Austenite Mn2NiGa materials show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn atoms at A and B sublattices. The magnetic moment of Mn atoms decrease greatly upon martensitic transformation to a tetragonal structure with a 50% reduction in Mn moments at the A site and almost completely suppressed Mn moments at B sites. Consequently, martensite Mn2NiGa alloys show ferromagnetic coupling. Different magnetic orderings in martensite and austenite also lead to very different temperature dependence, with which the abnormal behavior of magnetization upon martensitic transformation can be understood. In the off-stoichiometric samples with composition between Ni2MnGa and Mn2NiGa, we show that additional Mn atoms that substitute for Ni atoms in Ni2MnGa have the same magnetic behaviors as Mn in Mn2NiGa phase, which successfully explains the dependence of the magnetization on Mn composition.

Journal ArticleDOI
TL;DR: In this paper, the micro-fracture mechanisms of an UFAF pipeline steel are investigated by in situ tensile testing in a transmission electron microscope, and the results indicate that a grain-boundary-film structure composed of martensite/austenite could significantly influence the crack propagating behavior in the UfaF steel, consequently lowering the fatigue-crack growth rate by enhancing roughness-induced crack closure during cyclic loading.

Journal ArticleDOI
TL;DR: The microstructure of the white etching layer (WEL) on the contact surface of a head-hardened pearlitic rail was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a three-dimensional atom probe (3DAP) as mentioned in this paper.
Abstract: The microstructure of the white etching layer (WEL) on the contact surface of a head-hardened pearlitic rail was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a three-dimensional atom probe (3DAP). The WEL was confirmed to be composed of severely deformed pearlite lamellae as well as nanocrystalline martensite, austenite and cementite. The carbon atoms in the topmost surface of the WEL were distributed nearly uniformly. A few atomic percent of carbon was dissolved in the ferrite of the deformed pearlite lamellae. The maximum hardness was observed in the deformed pearlite region within the WEL rather than on the topmost surface layer. The microstructural feature of the WEL and the reason why the deformed layer shows a white contrast in optical microscopy are discussed.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the amount of reformed austenite in the heat-affected zone (HAZ) of submerged arc welded (SAW) duplex stainless steel 2205.
Abstract: The aim of the present work was to evaluate the amount of reformed austenite in the heat-affected zone (HAZ) of submerged arc welded (SAW) duplex stainless steel 2205. The model is based on calculations of the nucleation and growth of austenite. The present results are compared with other studies to evaluate the toughness properties and the probability of precipitation of brittle, intermetallic sigma phase. The results indicate that cooling the weld in air provides a satisfactory amount of reformed austenite and prevents formation of sigma phase.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the mechanism of surface modification associated with the high-current pulsed electron beam (HCPEB) treatment of a D2 steel with increasing numbers of pulses.

Journal ArticleDOI
TL;DR: In this paper, a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used.

Journal ArticleDOI
TL;DR: In this paper, the role of different constituents of dual phase steel during the BH effect was investigated in detail by means of precision dilatometry and X-Ray Diffraction (XRD).
Abstract: The increase in the yield stress of dual phase (DP) steels, resulting from the static strain ageing phenomenon, commonly referred to as bake hardening (BH), gives an important contribution to the additional in-service strength of outer auto body parts, e.g. with respect to the dent resistance of the components made with DP steel. In order to understand this large BH effect, the role of the different constituents of the DP steel during this process needs to be considered. The various stages of tempering phenomena taking place in the martensite phase were investigated in detail by means of precision dilatometry and X-Ray Diffraction (XRD). The succession of the various tempering reactions that are characterised by typical volume changes was determined using both constant heating rate and isothermal dilatometric tests. The measurements made it possible to distinguish five distinct stages of structural changes during tempering: (I) the redistribution of carbon atoms, (II) the precipitation of η- or e-carbide, (III) the formation of Hag-carbide, (IV) the decomposition of retained austenite, and (V) the transformation of transition carbides to cementite.

Journal ArticleDOI
TL;DR: In this article, the effect of heating mode on the densification, microstructure, strength and hardness of austenitic and ferritic stainless steel compacts was compared in a radiatively heated (conventional) and a 2.45 GHz microwave furnace.

Journal ArticleDOI
TL;DR: In this paper, the effect of deep cryogenic treatment on the hardness and wear resistance of carburized steels used in gears was studied and it was suggested the possibility of creation of nuclei sites during the 200-°C tempering, where new segregations of carbon and alloying elements could cluster during the cryogene treatment producing an increase in the hardness.

Journal ArticleDOI
TL;DR: In this article, the effect of hydrogen on the fatigue properties of alloys which are used in fuel cell (FC) systems has been investigated, and the results showed that there was a degradation in fatigue crack growth resistance due to hydrogen in the case of SUS304 and SUS316 austenitic stainless steels.

Journal ArticleDOI
TL;DR: In this paper, an AISI 301 metastable stainless steel is 90 pct cold-rolled and subsequently annealed at temperatures varying from 600 °C to 900 °C for a dwelling time of 30 minutes.
Abstract: Nano/submicron austenitic stainless steels have attracted increasing attention over the past few years due to fine structural control for tailoring engineering properties. At the nano/submicron grain scales, grain boundary strengthening can be significant, while ductility remains attractive. To achieve a nano/submicron grain size, metastable austenitic stainless steels are heavily cold-worked, and annealed to convert the deformation-induced martensite formed during cold rolling into austenite. The amount of reverted austenite is a function of annealing temperature. In this work, an AISI 301 metastable austenitic stainless steel is 90 pct cold-rolled and subsequently annealed at temperatures varying from 600 °C to 900 °C for a dwelling time of 30 minutes. The effects of annealing on the microstructure, average austenite grain size, martensite-to-austenite ratio, and carbide formation are determined. Analysis of the as-cold-rolled microstructure reveals that a 90 pct cold reduction produces a combination of lath type and dislocation cell-type martensitic structure. For the annealed samples, the average austenite grain size increases from 0.28 µm at 600 °C to 5.85 µm at 900 °C. On the other hand, the amount of reverted austenite exhibits a maximum at 750 °C, where austenite grains with an average grain size of 1.7 µm compose approximately 95 pct of the microstructure. Annealing temperatures above 750 °C show an increase in the amount of martensite. Upon annealing, (Fe, Cr, Mo)23C6 carbides form within the grains and at the grain boundaries.

Journal ArticleDOI
TL;DR: In this article, a case was constructed by a high volume fraction of Fe4N, Cr2N and CrN nitrides, leading to a low distortion of the parent austenitic phase, maintaining the original cubic lattice.
Abstract: Plasma nitriding of an AISI 316L austenitic stainless steel at low (400 °C) and high temperatures (550 °C) was performed under different nitriding gas mixtures. Nitrided surfaces were characterized by XRD using the Rietveld method. Expanded austenite “γN” with a special triclinic (t) crystalline structure was formed during the low-temperature nitriding treatment. Minor volume fractions of Fe3N, Fe4N and Cr2N nitrides were also found. The expanded austenite phase showed a distortion e of the lattice angles due to a very high nitrogen content dissolved in austenite, supersaturating the solid solution and leading to a 10% lattice distortion and to high compressive residual stresses at the surface. After nitriding the specimens at 550 °C the case was composed primarily by a high volume fraction of Fe4N, Cr2N and CrN nitrides, leading to a low distortion of the parent austenitic phase, maintaining the original cubic lattice.

Journal ArticleDOI
TL;DR: In this article, the electrochemical corrosion behavior of the NC 309 stainless steel (309SS) coating and the bulk steel in solutions of 0.25 M Na(2)SO(4) + 0.05 M H 2 SO(4 ) and 0.5 M NaCl+ 0.

Journal ArticleDOI
TL;DR: In this paper, the deformation microstructures of an Fe-27% Cr-9% Ni dual-phase stainless steel, which was bar rolled/swaged to a total strain of 6.9 at ambient temperature, were studied.

Journal ArticleDOI
TL;DR: In this paper, the structural and magnetic properties of Heusler alloy series Ni50 Mn50−x Snx (numbers indicate at. %) and Ni 50 Mn 50−x Inx have been studied and magnetization and calorimetric measurements have been carried out in order to study the magnetic and structural transitions properties.
Abstract: The structural and magnetic properties of Heusler alloy series Ni50 Mn50−x Snx (numbers indicate at. %) and Ni50 Mn50−x Inx have been studied. Magnetization and calorimetric measurements have been carried out in order to study the magnetic and structural transitions properties. The behaviour of the studied compounds is compared with that of the Ni–Mn–Ga alloy. Data for entropy and magnetization changes at the martensitic transition are reported. It is found that, as opposed to Ni–Mn–Ga, for Ni–Mn–In and Ni–Mn–Sn the magnetic moment in martensite is lower than in austenite.