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Cryogenic turning of metastable austenitic stainless steels can improve wear resistance of the resulting surface due to the phase transformation of γ‐austenite into α'‐ and/or ϵ‐martensite in the near surface layer. By using a cryogenic two‐step turning process, the amount of deformation‐induced α'‐martensite in the subsurface regime can be further increased. To determine the influence of the implemented and optimized two‐step turning strategy on the tribological properties of countersurfaces for radial shaft seals, an evaluation of wear behavior of the shaft seal countersurface as well as microstructural analyses in subsurface regime is presented and compared to the cryogenic single step turning process. The results show that not only the integral phase transformation in the overall subsurface region, but also the local phase distribution plays an important role when it comes to the surface performance in tribological applications. [ABSTRACT FROM AUTHOR]

The effects of heat treatment with continuous laser radiation on samples of the Fe–18Cr–10Ni alloy of the austenitic-martensitic class that have undergone preliminary megaplastic torsional deformation in the Bridgman chamber are investigated. It is established that the combined application of deformation (deformation in the Bridgman chamber) and thermal (laser heating) effects to the alloy forms the structure of metastable austenite (γ phase), which differs from stable austenite in higher strength characteristics. The nature of this phenomenon is discussed. [ABSTRACT FROM AUTHOR]

In recent years, medium manganese steels (MMSs) have garnered increased attention and interest due to their relatively low cost and superior combination properties compared to other steels. In particular, MMSs have been recognised as ideal wear-resistant materials employed in the mining industry. However, the studies on their wear performance have a lack of systematic documentation. This review provides an extensive overview of recent advances in the wear performance of MMSs, starting from discussions on applicable wear testing methods and typical wear testing results, followed by a further discussion on the wear mechanisms of MMSs based on five wear characteristics, including abrasive wear, adhesive wear, corrosive wear, fatigue wear and impact wear. The effects of hardness and hardened layers on the wear mechanisms are also discussed. Finally, the influence of phase constitution and microstructure on the wear performance of MMSs are comprehensively elaborated in terms of transformation induced plasticity (TRIP), twinning induced plasticity (TWIP), alloy elements and heat treatment. The key factors that affect the wear performance of MMSs include the elemental composition in MMSs and the phase transformation occurred during TRIP and TWIP as well as various heat treatment processes. The current review of key factors affecting the wear performance of MMSs sheds some light on new strategies to enhance the service performance and longevity of wear resistant steels in various engineering applications. [ABSTRACT FROM AUTHOR]

This paper evaluates the suitability of the X-ray diffraction (XRD) technique to characterize the phase transformation during the metal forming of the metastable austenitic steel AISI 304L. Due to plastic deformation, phase transformation from γ-austenite into α′-martensite occurs. The XRD peaks at specific 2θ diffraction angles give information about the phase amount. Analyses of the results with different characterization techniques such as microscopic analysis, including electron backscatter diffraction (EBSD), macro- and microhardness tests and magneto-inductive measurements of α′-martensite, were carried out. A qualitative and quantitative correlation to compute the amount of α′-martensite from the XRD measurements was deduced. XRD was validated as a suitable technique to characterize the phase transformation of metastable austenites. Additional data could provide necessary information to develop a more reliable model to perform a quantitative analysis of the phases from XRD measurements. [ABSTRACT FROM AUTHOR]

Introduction: A full three-dimensional (3D) microstructure characterization that captures the essential features of a given material is oftentimes desirable for determining critical mechanisms of deformation and failure and for conducting computational modeling to predict the material’s behavior under complex thermo-mechanical loading conditions. However, acquiring 3D microstructure representations is costly and time-consuming, whereas 2D surface maps taken from orthogonal perspectives can be readily produced by standard microscopic procedures. We present a robust and comprehensive approach for such 3D microstructure reconstructions based on three electron backscatter diffraction (EBSD) maps from orthogonal surfaces of two-phase materials.Methods: It is demonstrated that processing surface maps by spatial correlation functions combined with principal component analysis (PCA) results in a small set of unique descriptors that serve as a representative fingerprint of the 2D maps. In this way, the differences between surface maps of the real microstructure and virtual surface maps of a reconstructed 3D microstructure can be quantified and iteratively minimized by optimizing the 3D reconstruction.Results: To demonstrate the applicability of the method, the microstructure of a metastable austenitic steel in the two-phase region, where austenite and deformation-induced martensite coexist at room temperature, was characterized and reconstructed. After convergence, the synthetic 3D microstructure accurately describes the experimental system in terms of physical parameters such as volume fractions and phase shapes.Discussion: The resulting 3D microstructures represent the real microstructure in terms of their characteristic features such that multiple realizations of statistically equivalent microstructures can be generated easily. Thus, the presented approach ensures that the 3D reconstructed sample and the associated 2D surface maps are statistically equivalent.

The two‐body abrasive wear properties of metastable austenitic steels (MAS) against SiC abrasive paper are investigated at different wear loads. To ensure a metastable austenitic microstructure, the alloying compositions are chosen such that the martensite start temperature of the MAS is approximately at room temperature, while the proportions of carbon, manganese, and aluminum change. The abrasion test results are compared to martensitic (40MnB5) and austenitic steel (Hadfield steel). An up to four times lower weight loss is found for the MAS compared to the Hadfield steel and up to 6.7 times lower weight loss compared to the martensitic steel. It is found that the wear resistance of the MAS increases significantly with wear load. Wear resistance of over 1300 Nm mm−3 is achieved at the highest wear load of 32 N. The wear properties of the MAS are associated with an increase in the surface hardness resulting from a mechanically induced austenite to martensite phase transformation. It is shown that the addition of aluminum to the MAS reduces the wear resistance. This is explained by an increase in stacking fault energy and the associated restriction of the mechanically induced transformation to martensite. [ABSTRACT FROM AUTHOR]

In recent years, medium manganese steels (MMSs) have garnered increased attention and interest due to their relatively low cost and superior combination properties compared to other steels. In particular, MMSs have been recognised as ideal wear-resistant materials employed in the mining industry. However, the studies on their wear performance have a lack of systematic documentation. This review provides an extensive overview of recent advances in the wear performance of MMSs, starting from discussions on applicable wear testing methods and typical wear testing results, followed by a further discussion on the wear mechanisms of MMSs based on five wear characteristics, including abrasive wear, adhesive wear, corrosive wear, fatigue wear and impact wear. The effects of hardness and hardened layers on the wear mechanisms are also discussed. Finally, the influence of phase constitution and microstructure on the wear performance of MMSs are comprehensively elaborated in terms of transformation induced plasticity (TRIP), twinning induced plasticity (TWIP), alloy elements and heat treatment. The key factors that affect the wear performance of MMSs include the elemental composition in MMSs and the phase transformation occurred during TRIP and TWIP as well as various heat treatment processes. The current review of key factors affecting the wear performance of MMSs sheds some light on new strategies to enhance the service performance and longevity of wear resistant steels in various engineering applications.

This paper evaluates the suitability of the X-ray diffraction (XRD) technique to characterize the phase transformation during the metal forming of the metastable austenitic steel AISI 304L. Due to plastic deformation, phase transformation from γ-austenite into α′-martensite occurs. The XRD peaks at specific 2θ diffraction angles give information about the phase amount. Analyses of the results with different characterization techniques such as microscopic analysis, including electron backscatter diffraction (EBSD), macro- and microhardness tests and magneto-inductive measurements of α′-martensite, were carried out. A qualitative and quantitative correlation to compute the amount of α′-martensite from the XRD measurements was deduced. XRD was validated as a suitable technique to characterize the phase transformation of metastable austenites. Additional data could provide necessary information to develop a more reliable model to perform a quantitative analysis of the phases from XRD measurements.

This study investigated the effect of dislocation density on microstructural transformation and mechanical properties of Fe-7.23Mn-4.42Al-0.09C-1.99Si (wt.%) steel. By the tempering treatment, the dislocation density was reduced. The effect of of dislocation density on the plasticity of the steel was analyzed. The dislocation density was reduced from 2.3 × 10−16 m−2 to 1.6 10−16m−2 by tempering. Reducing dislocation density in the metastable austenite resulted in a higher metastable austenite transformation rate. And the low dislocation density steels exhibited a longer strain length during tensile deformation. It was obvserved that the dislocation density of the test steel decreased by 30% after tempering, the austenite transformation rate increased to 53.3%, and tensile strength and elongation increased to 1010 MPa and 44% respectively. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the principle universality of obtaining in the steel and cast iron structure, along with other constituents of residual metastable austenite undergoing dynamic deformation martensitic transformation or DDMT (self-hardening effect under loading or SHL) to increase their abrasive wear resistance. It was established that to provide increased resistance to abrasive wear, it is necessary, along with tempered martensite, lower bainite, and carbides, to obtain in the structure 20–40% of metastable austenite (35–42% in cast irons and 60–100% in manganese steels), a significant part of which transformed under abrasive action into deformation martensite. The wear resistance can be increased by 1.2–1.7 times. The practical significance of the proposed principle lies in the fact that it opens new possibilities in increasing the abrasive wear resistance of many steels and cast irons by obtaining metastable austenite in their structure at its optimal amount and stability. The principle can be implemented by various harden-ing heat treatment technologies used in the industry, the modes of which must ensure obtaining the appropriate structure, and not achieving the highest hardness, as is customary in many cases. [ABSTRACT FROM AUTHOR]

Steels with a certain amount of retained metastable austenite derived from e.g. heat treatment can undergo martensitic transformation induced by mechanical loads. Pre-machining is of high relevance for the following processes. Milling and grinding were chosen here for the pre-machining with subsequent deep rolling of 18CrNiMo 7-6 (AISI 4820) in carburized and carbonitrided states. Deep rolling is used to improve the surface and subsurface strength by inducing compressive residual stresses, strain hardening, and in this case martensitic transformation. The results of this paper show clearly that the pre-machining is sufficient to generate mechanically induced martensite and enhance the surface regarding the resulting hardness. These changes of the surface integrity are affecting the following deep rolling process, which is why a constant pre-machining is necessary for future investigations in order to compare deep rolling processes across each other. [ABSTRACT FROM AUTHOR]

The paper studies the transformation-induced plasticity of steel chromium-nickel-molybdenum structure depending on the reduction ratio during warm rolling. Optical and atomic force microscopies provide the surface profiling information. The parameters of the main structural elements such as the austenite grain size and martensite laths, width and height of twins are determined in this paper. It is shown that the reduction ratio has no significant effect on the volume fraction of the martensite phase, but changes martensite into lath martensite with high dispersity. The austenite strain hardening during rolling causes a four-fold increase in the yield point and a two-fold increase in the microhardness as compared to the initial state of the austenite steel. [ABSTRACT FROM AUTHOR]

It is shown that the wear resistance of graphitized steel under abrasive action and dry sliding friction can be increased by heat treatment that forms an increased content of metastable residual austenite in the steel structure, which undergoes dynamic strain martensitic transformation (DSMT), the self-quenching effect under loading, (SQL). In order to obtain an optimal content of metastable retained austenite (36%) in the structure of graphitized steel along with tempered martensite and graphite, as well as to achieve the highest relative abrasive wear resistance (εa = 4.8) and wear resistance in dry sliding friction (εdsf = 2.8) than occurs after routine heat treatment (εa = 3.5) and (εdsf = 2), heating to 950°С is required before quenching. Isothermal quenching, including austenitization at 850°C, cooling in water to an isothermal temperature of 300°C, holding for 10 min at this temperature in a furnace, and a subsequent cooling in air led to a slight increase in the relative abrasive wear resistance (εa= 3.8) as compared to the standard heat treatment (εa = 3.5). This procedure provides a significantly higher relative wear resistance of graphitized steel under dry sliding friction (εdsf = 3.6) than one could provide by routine quenching from a commonly used temperature (εdsf = 2), or by quenching from an elevated temperature (εdsf = 2.8) together with low-temperature tempering. The use of the proposed treatment procedures for graphitized steel should provide an increase in the durability of tools made of such a material and reduce the costs for purchasing it. [ABSTRACT FROM AUTHOR]

A novel concept of hybrid treatment for steels is presented. The goal is to produce a hard interstitially hardened/stabilized austenite layer, with an expected improved wear and corrosion resistance, in the surface of high‐hardenability steels. The novelty is in the fact that the thermochemical treatment is performed in the steel metastable austenite field, above the martensite start temperature, during the isothermal step of the martempering or austempering hardening treatment. As a proof of concept, CA6NM martensitic stainless steel samples are subjected to the novel hybrid treatment. The whole treatment is plasma assisted and the chosen thermochemical treatment is nitriding. In the presented case, the produced hard layer is constituted of N‐stabilized austenite. During the paraequilibrium thermochemical treatment step, the metastable austenite surface is converted into a hard interstitially hardened/N‐stabilized austenite. Once concluded the whole treatment, as the component is cooled down to the room temperature, surface does not undergo phase transformation, whereas the nonchemically altered substrate bulk undergoes metastable austenite to martensite phase transformation. So, by means of this case study, the feasibility and potentiality of this novel concept of hybrid treatment is proved. [ABSTRACT FROM AUTHOR]

It has been established that heating of a low-carbon deposited metal containing ~5, ~8 % Mn and additionally ~3% Cr having a martensitic structure to an intercritical temperature interval (ITI) provides a secondary metastable austenite, which undergoes a dynamic deformation martensitic transformation (self-hardening effect under loading). This significantly increases the wear resistance at dry sliding friction and impact abrasive action of the shot stream. The deposited metal with a higher manganese content (~14%) yield to the wear resistance under conditions of dry sliding friction of a metal containing 5% and 8% of manganese, but has a higher wear resistance than it when subjected to impact-abrasive action of the shot stream. [ABSTRACT FROM AUTHOR]

The change in the structure of welds made with a new welding wire and subjected to high-velocity impact was investigated by optical and scanning electron microscopy and X-ray diffraction analysis. It is shown that after welding, a structure consisting of martensite, δ -ferrite, and metastable austenite is formed in the weld metal. The subsequent severe impact leads to hardening of the weld metal due to the transformation of metastable austenite to strain-induced martensite. Kinetic microindentation of the weld was performed. [ABSTRACT FROM AUTHOR]

Abstract—The possibility of increasing the wear resistance of ductile VCh500-7 iron by isothermal quenching using a new method is studied. It differs in that cooling and holding are carried out according to the water–furnace scheme, not in a molten salt and alkali, as in the current technology. An increased level of wear resistance is achieved by obtaining in the structure, along with lower bainite and graphite, 20–37% metastable residual austenite. The isothermal quenching according to the new method is environmentally friendly and more economical than that currently used. [ABSTRACT FROM AUTHOR]

Introducing reverted austenite at lath martensite boundaries has been shown to be an effective method to increase the ductility of martensitic steels. However, significant strength reductions can also be introduced during the reversion process in martensitic stainless steels. To overcome the strength-ductility trade-off, we explore the effects of alloying elements in delaying the overaging of the precipitates and accelerating the austenite formation. To this end, we carry multi-objective optimization considering (1) lattice misfit and diffusivity for kinetics of precipitation, and (2) austenite fraction and thermodynamic driving force of austenite reversion for austenite formation. With the insights from calculations, model alloy compositions are then proposed, and mechanical testing and microstructural analysis are applied. The model alloy confirms that a relatively higher volume fraction of austenite can form prior to overaging, which doubles the total elongation without significant strength loss. [Display omitted] [ABSTRACT FROM AUTHOR]

• Low cycle fatigue of metastable austenitic steel. • Instrumented strain-controlled fatigue testing. • Fatigue life evaluation by short time evaluation procedures. • Open circuit potential as NDT parameter. Due to aging nuclear power plants there is an increasing need for methods to evaluate the integrity of components and structures of nuclear engineering. During power plant operation, nuclear materials are exposed to the effects of temperature, corrosion and cyclic loading. These lead to microstructural changes resulting in material degradation, which can be detected by suitable nondestructive testing (NDT) methods. Fatigue testing setups for ambient temperature, distilled water and 300 °C were designed to represent relevant environmental conditions and instrumented with in-situ measurements of temperature, electric, micromagnetic and electrochemical NDT parameters. Constant amplitude and strain increase tests with specimens of metastable austenitic stainless steel AISI 347 (X6CrNiNb18-10, 1.4550) typically used for pipe components were conducted in total strain control. Data obtained were employed in short-time evaluation procedure StrainLife to generate fatigue life data. To establish an understanding between microstructure evolution and NDT data, scanning electron microscopic methods such as electron backscatter diffraction and energy dispersive X-ray spectroscopy were used. Electrochemical data yields fatigue life results as good as conventionally used parameters like stress and strain. These findings could enable usage of presented parameters for mobile or even online testing systems, since accessibility depending on application case can be much improved. [ABSTRACT FROM AUTHOR]

Phase transitions during crystallization and subsequent thermal and deformation effects under the influence of various mechanical loads in welded joints of the plates of medium carbon steel by a consumable electrode in shielding gases with a flux-cored wire based on Fe–C–Cr matrix are studied. The test results for weldability, abrasive wear resistance, and stress state formation and the results of metallographic, electron microscopic, and X-ray diffraction studies are analyzed. It is shown that the structure of welded seam consists of metastable austenite, δ-ferrite, and high-strength carbon–chromium martensite. Welded joints have a high capability of intense hardening under local deformation owing to the TRIP effect (transformation-induced plasticity). [ABSTRACT FROM AUTHOR]

Diffusion and homogenization in "iron (5 μm–nickel (5 μm or 50 nm)" powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the "iron–nickel" powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels. [ABSTRACT FROM AUTHOR]

Some developments by Academician V.N. Antsiferov and his scientific school are considered from the viewpoint of their further development when fabricating structural powder materials and products. The prospects of work for the fabrication of concentration-inhomogeneous and trip steels are noted. There is great potential in the possibility of controlling the thickness and volume of the zone of the deformation martensite transformation occurring during the fracture. It is advisable to continue works on the fabrication of fullerene-containing and nitrogen-containing powder compositions, as well as on studying the structural heredity of powder steels. The possibility of synthesizing fullerene-containing phases during the liquid-phase sintering of "iron–cast iron" and "iron–graphite" compositions and their subsequent redistribution in the material bulk during dynamic hot pressing deserves attention. It is reasonable to fabricate nitrogen-containing steels by the mechanical activation of powders with subsequent sintering in dissociated ammonia not only when forming wear-resistant and corrosion-resistant steels, but also heat-resistant materials. Works on studying the decomposition of supercooled austenite in powder steels of various alloying systems having different process prehistories (sintered, hot-deformed, infiltrated, etc.) are promising. Works on studying hot deformed concentration-inhomogeneous materials fabricated, in particular, based on powders of the Distaloy type, are promising. Original procedures developed by the school of Academician V.N. Antsiferov are valuable. This is, in particular, the procedure of determining the concentration variation coefficient, as well as the magnitometric complex and mathematical model providing the possibility to forecast the decomposition of supercooled austenite. Works by V.N. Antsiferov can be in-demand when solving the problem of lean alloyed powder steels with a lower bainite structure, which provide the optimal combination of strength and viscosity. [ABSTRACT FROM AUTHOR]

Optical and scanning electron microscopy, as well as X-ray diffraction analysis, have been used to study the structural changes in the welded joints of steel structures subjected to a local severe dynamic action. It has been shown that after welding, a structure consisting of martensite, δ ferrite, and metastable austenite is formed in the weld metal. The subsequent severe dynamic action leads to a strengthening of the weld metal, which is caused by the transformation of metastable austenite into strain-induced martensite. [ABSTRACT FROM AUTHOR]

Stainless steel with appropriate phase composition and improved physicomechanical properties for use in the production of titanium sponge is developed. A production system is proposed for 03Kh17N3G9MBDYuch steel, taking account of the martensitic transformation in cold deformation. [ABSTRACT FROM AUTHOR]

Abstract A fine-grained AISI 304 austenitic stainless steel (ASS) was fabricated by cryogenic-rolling and cycle annealing. The fine-grained ASS was pre-strained to various strains of 0–0.16, and the corresponding microstructures, kinetics of strain-induced α ′-martensite (SIM α ′) and work-hardening behavior were investigated based on quantitative characterization, interrupted-tensile tests and physical metallurgy. We find that the yield strength of the ASS can be enhanced by combining grain-refining with pre-straining due to the strengthening effect of grain-refinement, dislocations, shear bands and SIM α ′. The formation rate of shear band increases with increasing pre-strain (ε p) and the probability for an intersection of shear band to form a SIM α ′ embryo is insensitive to the pre-strain, and as a result, the kinetics of SIM α ′ is accelerated by pre-straining. The fine-grained ASS with ε p ≈ 0–0.16 display a three-stage work-hardening behavior, and the corresponding Stage I, II and III are completed in advance mainly due to their faster kinetics of SIM α ′ and severer dynamic recovery caused by pre-straining. The work-hardening rate (Θ) of pre-strained fine-grained ASS decreases faster than that of non-pre-strained counterpart at Stage I, accompanying with dislocations-dominated hardening. The Θ ascend with increasing strain to a peak value at Stage II and then decline continuously to necking at Stage III, following as SIM α ′ -governed hardening, which can be tailored by grain-refining and pre-straining. Our studies provide the direct experimental evidence for the pre-straining to trim the kinetics of SIM α ′ in a fine-grained ASS. These observations help to deepen understanding of the effect of pre-strain on the mechanical behavior of other fine-grained strengthening ASS and transformation-induced-plasticity (TRIP) assisted alloy. [ABSTRACT FROM AUTHOR]

In the present study, quenching and partitioning (Q & P) treatment of a medium-carbon silicon-rich steel was processed by a dilatometer. The volume fraction of the retained austenite at different partitioning times was determined by X-ray diffraction (XRD). The metastable austenite transformation process after different partitioning times was studied by a combination of dilatometry, XRD, and transmission electron microscopy (TEM). Analysis of the transformation kinetics of metastable austenite during partitioning by means of dilatometry and the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation was carried out. The results show that the volume fraction of retained austenite increases first and then decreases with the increase of the partitioning time. The transformation active energy Q = 141 kJ·mol−1 and the Avrami exponent n = 1. The transformation product of metastable austenite is needle-like bainite, which grows perpendicularly towards the boundary of the austenite. Finally, the blocky austenite was divided into lath-shaped forms.

The kinetics of strain-induced martensite (SIM) formation in a Ti-bearing 201L stainless steel were evaluated and compared to the existing results of two conventional stainless steel grades; i.e., 201L and 304L AISI. The effects of strain rate and rolling pass reduction on the kinetics of SIM formation during cold rolling were investigated. The Ti-microalloying was found to be intensifying the transformation due to lowering the stacking fault energy. It was seen that decreasing the rolling pass reduction strongly affected the variation of SIM volume fraction. Furthermore, a close correlation between the hardness and strain-induced transformation was found arising from microstructural evolution during the cold rolling process. Three stages in the hardening behavior were detected associated with lath-type martensite formation, transition stage of martensite laths break up and formation of dislocation-cell-type martensite.

Abstract In the current study, a high-carbon, high-silicon steel (1.21 wt% C, 2.56 wt% Mn, 1.59 wt% Si) was subjected to different heat treatments ((a) quenching from 800–1000 °C; (b) quenching from 800–1000 °C with further bainitizing at 250 °C for 8 days), resulting in microstructures consisting (a) of austenite and martensite (up to 94 vol% austenite) or (b) of austenite, nanobainite, and tempered martensite (up to 39 vol% nanobainite). The work is carried out using SEM, XRD, microhardness measurement, surface profile characterization, and two-body abrasion testing. It was found that steel wear behaviour is strongly dependent on austenite volume fraction and its metastability to mechanically-induced martensite transformation under wear. Austenite enrichment with carbon (upon carbides dissolution or bainite transformation) inhibits mechanically-induced transformation leading to decrease in microhardness increment after wear test and to an increase in wear rate. Specimens as-quenched from 900–1000 °C are found to have the highest wear resistance. This is attributed to the higher metastability of the retained austenite of these specimens. Nanobainite-containing specimens exhibit suppressed TRIP-effect under abrasion. The specimens containing 60–94 vol% of metastable austenite are by 1.5–1.8 times more wear resistant compared with the specimens consisting of 10–39 vol% nanobainite and 49–55 vol% of more stable austenite. Also, the relationship between wear behaviour and surface profile of the worn specimens is discussed. Highlights • High-silicon 120Mn3Si2 steel was two-body abrasion tested under different microstructure state. • Metastable austenite exhibits better wear behaviour as compared with nanobainite. • Mechanically-induced transformation crucially enhances work hardening and wear resistance. • Nanobainite has more stable austenite due to higher carbon enrichment. [ABSTRACT FROM AUTHOR]

Abstract A computational study is conducted to examine the influence of mechanical twins on the kinetics of martensitic transformation in TRIP-maraging steel. Simulations are performed using a non-local crystal plasticity (CP) phase transformation model describing the deformation behavior of TRIP-maraging steel. This work is inspired by the experimental observations of Wang et al. (2014), where authors reported a twinning induced stability against the phase transformation in austenite islands embedded in the martensitic matrix. Finite element (FE) analysis is used to simulate the stability of austenite against the phase transformation in the presence and absence of mechanical twins, respectively. Depending on the parent crystal orientation, macroscopic outcome of FE calculations manifested a slower/faster transformation kinetics for austenitic islands with mechanical twins as compared to islands without twins which is found to be in a good qualitative agreement to experimental observations. Models with two austenite islands of different sizes confirmed the twinning induced alteration in the transformation kinetics. Microscopic observations from the simulations demonstrated that the twin orientations generated during mechanical twinning are less or more favorable for the strain induced or stress assisted transformations. This directly indicates that the basis of the alteration in the transformation kinetics could be the strong orientation dependence of the martensitic transformation. Thus, a model based analysis was used to explain the experimental findings related to phase transformation kinetics of TRIP-maraging steels. [ABSTRACT FROM AUTHOR]

Abstract The microstructure of martensite formed athermally or via deformation in Fe-Cr-Ni alloys with different austenite (γ) stability has been investigated using microscopy. Two different types of microstructures, viz. blocky and banded structure, are observed after athermal and deformation-induced martensitic transformation (AMT and DIMT, respectively). The blocky structure form during AMT or DIMT if the stability of γ is low. In both cases, there is a significant chemical driving force for the transformation from γ to α′-martensite (α′), and if it is not hindered by e.g. planar defects it can grow uninhibited into a blocky morphology without the necessity to nucleate new crystallographic variants to accommodate the transformation strains. On the other hand, the banded structure is due to the formation of ε-martensite (ε) during AMT, or the wider concept shear bands in the case of DIMT. The shear bands, and in particular ε, lower the nucleation barrier for α′ that forms within individual shear bands if the stability of γ is low. Neighbouring α′ units predominantly have a twin-related orientation relationship to accommodate the transformation strains. With increasing γ stability during DIMT, variant selection becomes pronounced with preferred formation of variants favorable oriented with respect to the applied stress/strain field. The formation of α′ at individual shear bands is also rare, since no ε is present and instead α′ forms at the intersection of shear bands for more stable γ. In conclusion, AMT and DIMT for low γ stability lead to similar microstructures, whereas the DIMT microstructure for high γ stability is distinct. Graphical abstract Image 1 Highlights • The formation of blocky α′ is related to the relatively low stability of γ. • The formation of banded structure is related to the assistance of ε. • The α′ variant pairing in Fe-Cr-Ni alloys with low SFE is twin-related. • The variant selection can be rationalized by Schmid law and double shear theory. [ABSTRACT FROM AUTHOR]

A physical-mathematical model was developed. It describes formation of a structure of deposited metal of Fe-Cr-Mn alloying system and binds its chemical composition, critical points of martensite transformation ( Mi, Mf), phase-structure state and nature of their layer-by-layer variation on thickness of the deposited metal. The model allows designing and regulating chemical and phase compositions (austenite, austenite-martensite, martensite-austenite, martensite) of metal of Fe-Cr-Mn alloying system deposited on steel St3 that provides the possibility to regulate service properties of the deposited metal. Specific conditions of operation of the deposited parts require selection of phase composition of the deposited metal (content of quenching martensite and metastable austenite), level of γ-phase metastability providing optimum development of deformation γ→α´ transformation and acquiring of the most significant effect of strengthening in process of testing and operation. 14 Ref., 1 Tabl., 5 Fig. [ABSTRACT FROM AUTHOR]

A physical-mathematical model was developed. It describes formation of a structure of deposited metal of Fe-Cr-Mn alloying system and binds its chemical composition, critical points of martensite transformation (Ms, Mf), phase-structure state and nature of their layer-by-layer variation on thickness of the deposited metal. The model allows designing and regulating chemical and phase compositions (austenite, austenite-martensite, martensite-austenite, martensite) of metal of Fe-Cr-Mn alloying system deposited on steel St3 that provides the possibility to regulate service properties of the deposited metal. Specific conditions of operation of the deposited parts require selection of phase composition of the deposited metal (content of quenching martensite and metastable austenite), level of g-phase metastability providing optimum development of deformation γα'-transformation and acquiring of the most significant effect of strengthening in process of testing and operation. 14 Ref., 1 Table, 4 Figures. [ABSTRACT FROM AUTHOR]

The influence of transformation induced plasticity (TRIP) on materials mechanical behaviours, as well as failure phenomena including crack propagation and phase boundary debonding in multiphase steels (e.g. dual phase steels, TRIP steels) are studied by using an advanced crystal plasticity finite element method. We have coupled the crystal plasticity model Ma and Hartmaier (2015), which explicitly considers elastic-plastic deformation of ferrite and austenite, austenite-martensite phase, with a cohesive zone model designed for crack propagation, to study the deformations of several representative microstructural volume elements (RVE). Results shows that, the transformation induced plasticity enhances materials strength and ductility, hinders crack propagation and influences interface debonding. Furthermore, the martensitic transformation kinetics in TRIP steels was found depending on the crystallographic orientation and the stress state of a retained austenite grain. The current simulation results helps to investigate and design multiphase steels with improved mechanical properties. [ABSTRACT FROM AUTHOR]

The possibility of increasing the abrasive wear resistance of tool steels by obtaining a multiphase structure including tempering martensite, carbides, and metastable austenite undergoing dynamic deformation martensitic transformation (DDMT) under abrasive action is shown. [ABSTRACT FROM AUTHOR]

An AISI 304 austenitic stainless steel (ASS) with various ultrafine- or fine-grained structures was fabricated by cold- or cryogenic-rolling and annealing. The microstructure and mechanical properties of the ultrafine- or fine-grained ASS were investigated based on statistical data and physical metallurgy. The results showed that much more volume fraction of α ′-martensite can be obtained by cryogenic-rolling in comparison with cold-rolling under a similar rolling strain, and ε -martensite was a medium to transform into α ′-martensite finally during cryogenic-rolling. The deformed ASS with larger volume fraction of α ′-martensite was beneficial to obtaining finer structure with a narrow distribution of grain sizes after the similar annealing process. The cycle annealing was a feasible method to make reverse transformation completely and to inhibit the structural coarsening simultaneously for the cold- or cryogenic-rolling ASS. The yield strength was enhanced by cryogenic-rolling and cycle annealing to be approximately 2.7 times higher than that of solution-treatment state. The tensile strength was not changed evidently, and the uniform strain was apparently decreased with reducing grain size. There is no significant relevance between the mechanical stability of austenite and average grain size for the ultrafine- or fine-grained ASS; however, their mechanical stability was less than that of solution-treatment state. [ABSTRACT FROM AUTHOR]

Warm caliber rolling at 550, 600, and 650 °C were carried out to refine the austenite grains of medium Mn steel by dynamic recrystallization (DRX). The effect of rolling temperature on the microstructure characteristics and mechanical properties of metastable austenitic steel was investigated in detail. The results show that the hierarchical structure of coarse fiber grains (CFGs) and ultrafine grains (UFGs) is obtained by warm caliber rolling method. With the increasing rolling temperature, more obvious DRX behavior occurs, resulting in a high percentage of UFGs. The preactive TRIP effect shortens the yield stress plateau in tensile stress-strain curves caused by CFGs with low stability. Furthermore, the unique hierarchical structure induces crack deflection and delamination, and significantly improves the impact toughness of medium Mn steel at room temperature. However, at the low temperature of −80 °C, CFGs are easy to induce martensite transformation, which seriously deteriorates the impact toughness. • Low caliber rolling temperature contributes to the formation of fiber grains. • Fiber grain structure improves the impact property at ambient temperature. • V-Carbide reduces the tensile and impact properties of the Medium Mn steel. • The martensitic transformation decreases impact properties at low temperature. [ABSTRACT FROM AUTHOR]

In this article, an attempt was made to determine the effect of dynamic load on the austempered ductile iron resistance obtained under different conditions of heat treatment. Tests were carried out on six types of cylindrical ductile iron samples austempered at 320, 370 and 400oC for 30 and 180 minutes. For each type of material, two samples were collected. As a next step in the investigations, the samples were subjected to a Taylor impact test. The samples after striking a non-deformable, rigid target were deformed on their front face. After Taylor test, a series of material tests was performed on these samples, noting a significant increase of hardness in the deformed part. This was particularly well visible in the ductile iron isothermally quenched at higher temperatures of 370 and 400oC. Inthezone of sample deformation, an increase in the content of ferromagnetic phase was also reported, thus indicating the occurrence of martensitic transformation in the microstructure containing mechanically unstable austenite. A significant amount of deformed graphite was also observed, which was a symptom of the deformation process taking place in samples. The ductile iron was characterized by high toughness and high resistance to the effect of dynamic loads, especially as regards the grade treated at a temperature of 370oC.

An AISI 304 austenitic stainless steel (ASS) with average grain size of approximately 48 µm was selected to explore the effect of the low-temperature on mechanical behavior for commercial metastable ASS, which basing on tensile tests and Charpy V-notch impact tests under temperatures of 20–298 K, Feritscope testing and physical metallurgy. The results showed that both yield strength and tensile strength were enhanced by lowering temperatures; however, the uniform strain decreased with reducing temperatures. The yield strength at 20 K and 77 K were much higher than that at other temperatures, accompanying with an abrupt increase of thermally-induced martensite before tensile testing. The Charpy V-notch impact energy decreased faster in the range of 77–298 K and kept almost unchanged in the range of 20–77 K, and the ASS at 20 K still exhibited a dimple shaped fracture. Generally, the work-hardening rate ( Θ ) of the ASS at testing temperatures of 20–298 K dropped rapidly at the initial plastic strain range (Stage I) and then grew with the increase of tensile strain (Stage II), then following by a continuous decline to necking (Stage III), i.e., the generation of a peak of work-hardening rate. Specifically, the Stage I, II and III were terminated in advance and the peak value at the Stage II were increased obviously by reducing temperature from 298 K down to the range of 20–253 K. Furthermore, the work-hardening behavior of the ASS was discussed in view of the evolution of microstructure basing on Olson-Cohen model. [ABSTRACT FROM AUTHOR]

Features of the change in microstructure of manganese white cast iron of grade ChG5D2F4 with the use of plasma action are studied. Plasma hardening treatment leads to an increase in wear resistance due to an optimum phase composition and degree of residual austenite metastability. [ABSTRACT FROM AUTHOR]

In this work, ausforming is applied to a newly developed stainless steel. This process consists of austenitisation, quenching to a deformation temperature above room temperature, deformation of the metastable austenitic microstructure without the formation of martensite, and subsequent quenching in liquid nitrogen. The investigated steel is explicitly developed to be processed by ausforming and manufactured as a laboratory size test melt. The aim is to achieve a steel having a high hardness as well as a high corrosion resistance. Instead of conventional quenching and tempering, conventional processing is followed by ausforming. A parameter study incorporating the austenitisation temperature and time, deformation temperature, deformation speed, and degree of deformation is performed to achieve maximum hardness. Furthermore, the influence of soft annealing prior to ausforming is also investigated. The hardness of ausformed specimens is measured and correlated to the parameters used for processing. The microstructure of selected specimens is also investigated. Surprisingly, small amounts of martensite are found after ausforming, although a hardness of about 600 HV10 is achieved. In fact, a highly deformed austenitic microstructure is found predominantly. [ABSTRACT FROM AUTHOR]

An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α') phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α'-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction. [ABSTRACT FROM AUTHOR]

Results are given for a study of the structure and mechanical properties of manganese powder steels prepared by hot forging of porous workpieces in the presence of a liquid phase. The presence of a liquid phase during hot recompaction reduces energy expended in deformation and also the probability of manganese oxidation and sublimation that facilitates an improvement in steel strength and ductility properties. [ABSTRACT FROM AUTHOR]

Fe-18Cr-8Ni and Fe-18Cr-8Ni-1Y (at%) stainless steel powders were nanostructured by mechanical alloying from elemental powders and subjected to 90 min annealing treatments at various temperatures. The microstructural evolutions as a function of alloy compositions and temperatures were investigated by in-situ and ex-situ x-ray diffraction experiments, transmission electron microscopy and focused ion beam microscopy. The dependence of hardness on the microstructure was utilized to study the mechanical changes. It was found that the resulting microstructures by mechanical alloying were bcc solid solution, the so-called α’-martensite structure. The high temperature in-situ x-ray diffraction experiments showed that the martensite-to-austenite reverse phase transformation was completed above 800 and 900 °C for Fe-18Cr-8Ni and Fe-18Cr-8Ni-1Y steels, respectively. A partial or complete retransformation to martensite was observed upon cooling to room temperature. Annealing of nanocrystalline Fe-18Cr-8Ni steel yielded grain growth reaching to micron sizes at 1100 °C while addition of 1 at% yttrium stabilized the microstructure around 160 nm grain size and 6 GPa hardness after 90 min annealing at 1200 °C. [ABSTRACT FROM AUTHOR]

In work is shown, that at the expense of application of rational modes tempering, superficial plastic deformation, cementation with the subsequent normalization, can be essentially increased wear resistance at dry friction of metal with structure metastable austenite, which received deposition by a wire ПП-Нп 14Х12Г12СТ.

Multiple strengthening methods, such as high dislocation density, high twin density, small grain size, and metastable austenite phase can give high strength to ultra-high strength steels (UHSSs). However, the high strength of UHSSs often results in a greater tendency for springback when applied in manufacturing vehicle components. In the present study, two types of UHSSs, dual-phase (DP) steel and quenching and partitioning (QP) steel are investigated to study the springback behavior during the bending process. Results indicated that both the strain heterogeneity and the transformation of retained austenite impacted the springback behavior. The springback angle of the DP steel increased with the increase in bending angle, which was caused by the increasing degree of strain heterogeneity. However, the springback angle of the QP steel decreased to a 14.75° when QP specimens were strained at a 104° bending angle due to the inhibiting effect of the phase transformation. This indicated that there was preferential phase transformation in the thickness direction in the retained austenite of the outer and inner zones. The phase transformation caused low strain heterogeneity, which resulted in a lower tendency for springback. The results suggested that QP steel could possess lower springback at a proper bending angle.