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High‐manganese steels are promising candidates for application in crash‐relevant automobile components due to their outstanding mechanical properties. These properties result from the activation of additional plasticity effects, such as transformation‐induced plasticity (TRIP) and twinning‐induced plasticity (TWIP). In the present study, we investigate the influence of thermomechanical treatment, specifically by reversion‐annealing, on the mechanical properties. Three alloys with varying stacking fault energy (SFE) values are used: a X8Mn23 TRIP steel (SFE≈5 mJ m−2), a X30Mn22 TWIP/TRIP steel (SFE≈16.3 mJ m−2), and a X30MnAl22‐1 TWIP steel (SFE≈25 mJ m−2). The objective of the study is to combine the beneficial influences of the TWIP and TRIP effect to tailor the mechanical properties. Bimodal microstructures are generated by pre‐deformation with subsequent reversion‐ or recovery‐annealing to correlate the influence of the different microstructural features with the tensile behavior. During reversion‐annealing at 350 °C for 2 min, the previously introduced ϵ‐martensite is transformed to soft austenite. At the same time, dislocations and deformation‐induced twin boundaries are thermally stable. Recovery‐annealing at 550 °C for 30 min results in the annihilation of dislocations, but retention of deformation twins. These bimodal microstructures, comprised of strong and soft austenite, facilitate an improved yield strength‐ductility combination. Reversion‐annealing of the TWIP/TRIP steel results in a slightly higher yield strength with lower total elongation, but decreased work‐hardening rates compare to the recovery‐annealed TWIP steel. [ABSTRACT FROM AUTHOR]

In recent years, high strength steels, particularly press-hardening steel, have been more extensively employed for manufacturing safety-relevant structural components in vehicle bodies. These applications require contrasting material properties such as extremely high strengths as well as high forming ductility. Owing to the purely martensitic microstructure, the residual ductility of the conventional press hardened steels is low. Quenching and partitioning heat treatments can fulfil the requirement of an increased residual ductility by stabilizing the retained austenite. Moreover, if the quenching and partitioning heat treatments are carried out after intercritical annealing treatment, then the steel's mechanical properties can be tailored by defining the volume fraction of ferrite in the microstructure. In order to determine the potential of an 1-step quenching and partitioning heat treatment combined with intercritical annealing processes, elevated contents of retained austenite are produced in ferritic-martensitic microstructures using the low-alloyed 22MnB5 steel grade. In addition to a tempered martensitic microstructure, secondary martensite, and a low fraction of retained austenite, the microstructure consists of remaining fractions of ferrite; thus, providing an additional increase in ductility. For this optimized microstructure, a yield stress of 513 MPa and a tensile strength of 1045 MPa are measured with a total elongation of 10.8%. [ABSTRACT FROM AUTHOR]

Metal-matrix composites (MMCs) are of high interest due to their combination of a ductile matrix with a hard phase for reinforcement. Besides the production via one of the various powder-metallurgical routes, it is also possible to cast MMCs by infiltrating a porous ceramic structure with liquid melt. In the presented work, the infiltration of a macroporous ceramic through gravity casting is described. The MMC described consists of high-alloyed metastable austenitic-martensitic CrMnNi-cast steel and a metastable zirconium dioxide ceramic. Both materials are able to transform martensitic if load is applied. To increase infiltration of the zirconia foam, sulfur has been added to the steel melt. After the casting, the wear behavior during three-body abrasive wear test of the MMC is examined. The MMC as well as the TRIP steel by itself shows a high improvement in wear resistance, when compared to other wear materials. In order to investigate the increased wear resistance, an XRD-evaluation is described. The amount of α′-martensite and ferrite changes from 26 to 97 vol% due to abrasive wear while no transformation of the metastable tetragonal Mg-PSZ can be observed. [ABSTRACT FROM AUTHOR]

High-alloy cold rolled TRIP/TWIP steels have a remarkable potential for crash-relevant structures. Electron beam welding (EBW) can be regarded as being predestined for this purpose due to, among other factors, its locally limited heat input. The aim of this work is the characterization of the influence of the welding conditions on the chemical composition, the microstructure, and the mechanical properties of high-alloy cold rolled TRIP/TWIP steels. Three CrMnNi steels are cold rolled and welded with different beam intensities. The microstructure of the weld seams (WS) and the heat-affected zones (HAZs) is characterized by means of light microscopy and scanning electron microscopy (SEM). The mechanical properties of the welded joints are evaluated by hardness measurements and tensile testing. The weld seams are defect-free and surrounded by narrow HAZs. The microstructures inside the HAZs exhibited recrystallization and reverse annealing effects and constituted the failure-relevant area of the weld. [ABSTRACT FROM AUTHOR]

In the present work the influence of phosphor on the flowability, the effect on the infiltration of ZrO2 open foam ceramics and the martensite formation as well as the resulting mechanical properties of high alloyed CrMnNi as-cast steels is studied. Additionally, the effect of phosphor on surface tension is investigated. The study is performed using thermodynamic calculations, static tensile tests, notch-bar impact tests, optical light microscopy, scanning electron microscopy, energy dispersive X-ray analysis, electron backscatter diffraction, and the magnetic scale for the detection of ferromagnetic phase fractions. Maximum bubble pressure method is used to measure the surface tension of the liquid steel. The martensite phase fraction is not significantly influenced with increasing phosphor content. The flowability and the quality of the infiltration of open foam ceramics are improved with increasing phosphor contents. The investigated specimens show an increasing yield and an ultimate tensile strength with higher phosphor contents. The uniform and the fracture elongation as well as the notch impact resistance remain at high values. Moreover, an increase in phosphor content did not significantly change the surface tension of the investigated CrMnNi alloys. [ABSTRACT FROM AUTHOR]

For the modeling of the mechanical behavior of a two phase alloy with the rule of mixture (RM), the flow stress of both phases is needed. In order to obtain these information for the α′-martensite in high alloyed TRIP-steels, compression tests at cryogenic temperatures were performed to create a fully deformation-induced martensitic microstructure. This martensitic material condition was subsequently tested under compressive loading at −60, 20, and 100°C and at strain rates of 10−3, 100, and 103 s−1 to determine the mechanical properties. The α′-martensite possesses high strength and surprisingly good ductility up to 60% of compressive strain. Using the flow stress behavior of the α′-martensite and that of the stable austenitic steel AISI 316L, the flow stress behavior of the high alloyed CrMnNi TRIP-steel is modeled successfully using a special RM proposed by Narutani et al. [ABSTRACT FROM AUTHOR]

A combined TWIP/TRIP effect has been observed in a high Mn cold rolled steel. The change in the magnetic property of the material with strain due to the austenite-to-martensite transformation has been measured and it shows increasing ferromagnetic behavior with strain. The texture development with strain has been analyzed via the Schmid factor for slip and twin systems in the material. The phase transformation has been related to changes occurring in the {110} <001> and {112} <111> texture components as well as to the profiles of XRD peaks at different strain levels. [ABSTRACT FROM AUTHOR]

The mechanical properties of high manganese steels are linked to their hardening mechanisms and their intrinsic behavior during deformation. The characterization of mechanical properties is influenced by the localization of plastic flow and the effect of this localization on the material. Depending on grain size, temperature, and extrinsic strain rate localization of strain, adiabatic heating, and hardening vary in spatial and temporal extent. Even at small strain rates the adiabatic heating of samples reaches temperatures more than 100 K over initial testing temperature due to the sharp localization and last but not least this heating is also dependent on the tested sample size. Furthermore, temperature influences the activated mechanisms of plastic flow. The characterization of temperature increase, strain distribution, and local hardening is pursued in tensile tests with application of infrared thermography. With those techniques it is possible to gather correlations between local strain and temperature. The analysis of dynamic strain ageing effects is also carried out by evaluation of the instantaneous strain rate, the strain rate in the gauge length, in dependence of stress in different alloys, as well as at different strain rate regimes. Thus it is possible to distinguish the onset of TRIP, TWIP and DSA. [ABSTRACT FROM AUTHOR]

Stress-Temperature-Transformation (STT) and Deformation-Temperature-Transformation (DTT) diagrams are suitable to characterize the TRIP (transformation-induced plasticity) and TWIP (twinning-induced plasticity) effect in steels. The triggering stresses for the deformation-induced microstructure transformation processes, the characteristic temperatures, the yield stress and the strength of the steel are plotted in the STT diagram as functions of temperature. The elongation values of the austenite, the strain-induced twins and martensite formations are shown on the DTT diagram. The systematics of STT and DTT diagrams and the method for their development are described. Especially, the correlations between the STT and DTT diagrams and the thermodynamics are explained in the present paper. The developed STT and DTT diagrams for a novel austenitic Cr-Mn-Ni (16%Cr, 6% Mn, 6% Ni) as-cast steel and austenitic steel AISI 304 are presented. The Cr-Mn-Ni steel shows a deformation-induced α′-martensite and twin formation. In contrast, the AISI 304 shows a deformation-induced ε- and α′-martensite formation. The differences between both steel grades are based on thermodynamic pre-conditions. Therefore the thermodynamic stability conditions of the phases and the kinetics of stress and deformation-induced martensite and the twins formation are reflected in the developed STT and DTT diagrams. [ABSTRACT FROM AUTHOR]

In the present work, the mechanical behaviour at different strain rates of a high strength tool steel with the composition FeCrVC (at.%), manufactured under relatively high cooling rates and highly pure conditions, was studied. The applied preparation conditions promote a microstructure composed of martensite, retained austenite and a fine network of special carbides already in the as-cast state. This special phase combination yields a structural material with superior mechanical properties under quasi-static loading, exhibiting an extremely high engineering compression strength of almost 4000 MPa combined with a large compression strain of about 20% due to deformation-induced martensite formation. However, the knowledge of the performance of this material under dynamic loading conditions is also very important for its possible application as a novel kind of tool steel. For this reason, compression tests in the strain rate range of 10-10 s were performed and the transformation-induced plasticity (TRIP effect) was investigated. The analysis of the transformation behaviour of the retained austenite reveals that the rate of martensite formation decreases with increasing strain rate. Furthermore, an increase of the offset yield stress and the compression strength with increasing strain rate together with a remarkable plasticity was detected. [ABSTRACT FROM AUTHOR]

Steels show different types of deformation mechanisms. Those mechanisms inherit different geometrical influences on the shape of grains on the materials surface and lead to changes in surface topography during deformation. Within the Collaborative Research Center SFB 761 - Steel Ab Initio a way of strain dependent microstructure characterization concerning deformation mechanisms of austenitic high manganese steels is evaluated. With the measurement of a polished surface with confocal microscopy it is possible to observe not only the macroscopic visible orange peel, but also the effects that occur on grain size level during deformation. In a practical approach in-situ measurements of surface topography are performed in incremental strain steps during tensile test. Each measurement delivers the evolution of surface roughness as well as information on the surface topography of single grains in a representative measurement area. The results of in situ confocal microscopy of 3 different steel concepts are presented and evaluated regarding the relevance of the technique for the deformation characterization. [ABSTRACT FROM AUTHOR]

The temperature dependence of the martensite formation and the mechanical properties of three high alloyed Cr-Mn-Ni as-cast steels with varying Ni contents were studied. The results showed that the M and M temperatures of the steels decrease with increasing nickel contents. Therefore the strain-induced martensite formation, the TRIP effect and the temperature anomaly of the elongations occurs at lower temperatures. The steel alloyed with 3% nickel shows a stress induced formation of martensite and a dynamic strain aging. Depending on the nickel content and the temperature a TWIP effect occurs additionally to the TRIP effect in the investigated steels. The study was performed by using static tensile tests, dilatometer tests, optical microscopy and the magnetic scale for the detection of ferromagnetic phase fractions. [ABSTRACT FROM AUTHOR]

In this study the influence of Mn on galvannealed coatings of 1.7% Mn-1.5% Al TRIP- and 23% Mn X-IP®-steels was investigated. It is shown that the external selective oxides like Mn, Al and Si of the TRIP steel which occur after annealing at 800 °C for 60 s at a dew point (DP) of -25 °C (5% H) hamper the Fe/Zn-reaction during subsequent galvannealing. Preoxidation was beneficially utilized to increase the surface-reactivity of the TRIP steel under the same dew point conditions. The influence of Mn on the steel alloy was investigated by using a 23% Mn containing X-IP®-steel which was bright annealed at 1100 °C for 60 s at DP -50 °C (5% H) to obtain a mainly oxide free surface prior to hot dip galvanizing (hdg) and subsequent galvannealing. As well known from the literature Mn alloyed to the liquid zinc melt stabilizes δ-phase at lower temperatures by participating in the Fe-Zn-phase reactions, it was expected that the metallic Mn of the X-IP®-steel increases the Fe/Zn-reactivity in the same manner. The approximation of the effective diffusion coefficient (D(Fe)) during galvannealing was found to be higher than compared to a low alloyed steel reference. Contrary to the expectation no increased Fe/Zn-reaction was found by microscopic investigations. Residual η- and ζ-phase fractions prove a hampered Fe/Zn-reaction. As explanation for the observed hampered Fe/Zn-reaction the lower Fe-content of the high-Mn-alloyed X-IP®-steel was suggested as the dominating factor for galvannealing. [ABSTRACT FROM AUTHOR]

The article presents a study which evaluates the microstructures and mechanical properties of transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels with different manganese (Mn) concentrations. The study has found that both TRIP and TWIP effects were observed in steel with lower concentration of Mn. Moreover, the TWIP effect was dominantly observed as the deformation mechanism in steel with higher concentration of Mn.

The article presents a study which examines the tensile properties of high manganese (Mn) austenitic steels after various solutions. The results of the study reveal that the solution has an important influence on microstructure and mechanical properties of the austenitic steels. The study shows that a solution treatment at low temperature within the austenitic range will result in a reduction in the grain size of the steel.

The article presents an analysis of the stability of retained austenite and the kenitics strain-induced martensitic transformation in micro-alloyed TRIP-iaded steel. It focuses on the tensile tests with single specimen and at variable temperature to determine the influence of the micro-alloying on the Msσ temperature of the retained austenite. The results of the stability of retained austenite and the kenitics of the strain-induced martensitic transformation are presented.

Forming processes such as rolling or forging require detailed knowledge of the flow of the stress and deformation behavior at hot working conditions. Therefore, the deformation behavior of 16‐7‐6 CrMnNi TRIP steel with 30 vol% MgPSZ composite is studied by hot‐compression tests at a strain rate of 1 s−1. And highly particle reinforced TRIP‐Matrix‐Composite in a temperature range between 700 and 1200 °C show obvious changes in the flow curve behavior. At 700 °C, a step like shape with plateaus is clearly pronounced. With increasing temperature, this effect is not observed but the flow curves are shifted to lower stresses. Furthermore, dynamic recrystallization is observed above 800 °C deformation temperature. To identify the deformation mechanisms as well as the failure mechanisms, the microstructure evolution is studied at 700 °C for different strain values. The microstructure is investigated using light‐optical and secondary electron microscopy (SEM). Local damage by particle fracture and void formation around particles is evident during deformation. Remarkably, the ceramic particles reorient with increasing strain to form a certain banding and therefore a structural anisotropy. [ABSTRACT FROM AUTHOR]