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4 pages, 160 KiB

Open AccessEditorial

Physical Metallurgy of High Manganese Steels

by Wolfgang Bleck and Christian Haase

Metals 2019, 9(10), 1053; https://doi.org/10.3390/met9101053 - 28 Sep 2019

Cited by 11 | Viewed by 2449

Abstract

The development of materials with advanced or new properties has been the primary aim of materials scientists for past centuries [...] Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

Research

Jump to: Editorial

14 pages, 5597 KiB

Open AccessArticle

Influence of Microstructural Morphology on Hydrogen Embrittlement in a Medium-Mn Steel Fe-12Mn-3Al-0.05C

by Xiao Shen, Wenwen Song, Simon Sevsek, Yan Ma, Claas Hüter, Robert Spatschek and Wolfgang Bleck

Metals 2019, 9(9), 929; https://doi.org/10.3390/met9090929 - 24 Aug 2019

Cited by 14 | Viewed by 4221

Abstract

The ultrafine-grained (UFG) duplex microstructure of medium-Mn steel consists of a considerable amount of austenite and ferrite/martensite, achieving an extraordinary balance of mechanical properties and alloying cost. In the present work, two heat treatment routes were performed on a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C [...] Read more.

The ultrafine-grained (UFG) duplex microstructure of medium-Mn steel consists of a considerable amount of austenite and ferrite/martensite, achieving an extraordinary balance of mechanical properties and alloying cost. In the present work, two heat treatment routes were performed on a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C (wt.%) to achieve comparable mechanical properties with different microstructural morphologies. One heat treatment was merely austenite-reverted-transformation (ART) annealing and the other one was a successive combination of austenitization (AUS) and ART annealing. The distinct responses to hydrogen ingression were characterized and discussed. The UFG martensite colonies produced by the AUS + ART process were found to be detrimental to ductility regardless of the amount of hydrogen, which is likely attributed to the reduced lattice bonding strength according to the H-enhanced decohesion (HEDE) mechanism. With an increase in the hydrogen amount, the mixed microstructure (granular + lamellar) in the ART specimen revealed a clear embrittlement transition with the possible contribution of HEDE and H-enhanced localized plasticity (HELP) mechanisms. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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14 pages, 1491 KiB

Open AccessArticle

Accelerated Ferrite-to-Austenite Transformation During Intercritical Annealing of Medium-Manganese Steels Due to Cold-Rolling

by Josh J. Mueller, David K. Matlock, John G. Speer and Emmanuel De Moor

Metals 2019, 9(9), 926; https://doi.org/10.3390/met9090926 - 23 Aug 2019

Cited by 13 | Viewed by 3642

Abstract

Prior cold deformation is known to influence the ferrite-to-austenite (α → γ) transformation in medium-manganese (Mn) steels that occurs during intercritical annealing. In the present study, a 7Mn steel with ultra-low residual carbon content and varying amounts of prior cold deformation was [...] Read more.

Prior cold deformation is known to influence the ferrite-to-austenite (α → γ) transformation in medium-manganese (Mn) steels that occurs during intercritical annealing. In the present study, a 7Mn steel with ultra-low residual carbon content and varying amounts of prior cold deformation was intercritically annealed using various heating rates in a dilatometer. The study was conducted using an ultra-low carbon steel so that assessments of austenite formation during intercritical annealing would reflect the effects of cold deformation on the α → γ transformation and Mn partitioning and not effect cementite formation and dissolution or paraequilibrium partitioning induced austenite growth from carbon. Increasing prior cold deformation was found to decrease the A_c1 temperature, increase austenite volume fraction during intercritical annealing, and increase the amount of austenite nucleation sites. Phase field simulations were also conducted in an attempt to simulate the apparent accelerated α → γ transformation with increasing prior cold deformation. Mechanisms for accelerated α → γ transformation explored with phase field simulations included an increase in the amount of austenite nucleation sites and an increased Mn diffusivity in ferrite. Simulations with different amounts of austenite nucleation sites and Mn diffusivity in ferrite predicted significant changes in the austenite volume fraction during intercritical annealing. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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17 pages, 15063 KiB

Open AccessArticle

On the Evolution of Residual Stresses, Microstructure and Cyclic Performance of High-Manganese Austenitic TWIP-Steel after Deep Rolling

by Torben Oevermann, Thomas Wegener and Thomas Niendorf

Metals 2019, 9(8), 825; https://doi.org/10.3390/met9080825 - 25 Jul 2019

Cited by 15 | Viewed by 3602

Abstract

The mechanical properties and the near surface microstructure of the high-manganese twinning-induced plasticity (TWIP) steel X40MnCrAl19-2 have been investigated after deep rolling at high (200

^{\circ} C

), room and cryogenic temperature using different deep rolling forces. Uniaxial tensile tests reveal an increase [...] Read more.

The mechanical properties and the near surface microstructure of the high-manganese twinning-induced plasticity (TWIP) steel X40MnCrAl19-2 have been investigated after deep rolling at high (200

^{\circ} C

), room and cryogenic temperature using different deep rolling forces. Uniaxial tensile tests reveal an increase in yield strength from 400 MPa to 550 MPa due to surface treatment. The fatigue behavior of selected conditions was analyzed and correlated to the prevailing microstructure leading to an increased number of cycles to failure after deep rolling. Deep rolling itself leads to high compressive residual stresses with a stress maximum of about 800 MPa in the subsurface volume characterized by the highest Hertzian pressure and increased hardness up to a distance to the surface of approximately 1

m

m

with a maximum hardness of 475 HV0.1. Due to more pronounced plastic deformation, maximum compressive residual stresses are obtained upon high-temperature deep rolling. In contrast, lowest compressive residual stresses prevail after cryogenic deep rolling. Electron backscatter diffraction (EBSD) measurements reveal the development of twins in the near surface area independently of the deep rolling temperature, indicating that the temperature of the high-temperature deep rolling process was too low to prevent twinning. Furthermore, deep rolling at cryogenic temperature leads to a solid–solid phase transformation promoting martensite. This leads to inferior fatigue behavior especially at higher loads caused by premature crack initiation. At relatively low loads, all tested conditions show marginal differences in terms of number of cycles to failure. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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12 pages, 4707 KiB

Open AccessArticle

The Influence of Warm Rolling on Microstructure and Deformation Behavior of High Manganese Steels

by Marco Haupt, Max Müller, Christian Haase, Simon Sevsek, Frederike Brasche, Alexander Schwedt and Gerhard Hirt

Metals 2019, 9(7), 797; https://doi.org/10.3390/met9070797 - 18 Jul 2019

Cited by 16 | Viewed by 3512

Abstract

In this work, a Fe-23Mn-0.3C-1Al high manganese twinning-induced plasticity (TWIP) steel is subjected to varying warm rolling procedures in order to increase the yield strength and maintain a notable ductility. A comprehensive material characterization allows for the understanding of the activated deformation mechanisms [...] Read more.

In this work, a Fe-23Mn-0.3C-1Al high manganese twinning-induced plasticity (TWIP) steel is subjected to varying warm rolling procedures in order to increase the yield strength and maintain a notable ductility. A comprehensive material characterization allows for the understanding of the activated deformation mechanisms and their impact on the resulting microstructure, texture, and mechanical properties. The results show a significant enhancement of the yield strength compared to a fully recrystallized Fe-23Mn-0.3C-1Al steel. This behavior is mainly dominated by the change of the active deformation mechanisms during rolling. Deformation twinning is very pronounced at lower temperatures, whereas this mechanism is suppressed at 500 °C and a thickness reduction of up to 50%. The mechanical properties can be tailored by adjusting rolling temperature and thickness reduction to desired applications. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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10 pages, 2746 KiB

Open AccessArticle

Comparison of the Dislocation Structure of a CrMnN and a CrNi Austenite after Cyclic Deformation

by Rainer Fluch, Marianne Kapp, Krystina Spiradek-Hahn, Manfred Brabetz, Heinz Holzer and Reinhard Pippan

Metals 2019, 9(7), 784; https://doi.org/10.3390/met9070784 - 13 Jul 2019

Cited by 5 | Viewed by 3525

Abstract

In the literature, the effects of nitrogen on the strength of austenitic stainless steels as well as on cold deformation are well documented. However, the effect of N on fatigue behaviour is still an open issue, especially when comparing the two alloying concepts [...] Read more.

In the literature, the effects of nitrogen on the strength of austenitic stainless steels as well as on cold deformation are well documented. However, the effect of N on fatigue behaviour is still an open issue, especially when comparing the two alloying concepts for austenitic stainless steels—CrNi and CrMnN—where the microstructures show a different evolution during cyclic deformation. In the present investigation, a representative sample of each alloying concept has been tested in a resonant testing machine at ambient temperature and under stress control single step tests with a stress ratio of 0.05. The following comparative analysis of the microstructures showed a preferred formation of cellular dislocation substructures in the case of the CrNi alloy and distinct planar dislocation glide in the CrMnN steel, also called high nitrogen steel (HNS). The discussion of these findings deals with potential explanations for the dislocation glide mechanism, the role of N on this phenomenon, and the consequences on fatigue behaviour. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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9 pages, 7298 KiB

Open AccessArticle

Improving Mechanical Properties of 18%Mn TWIP Steels by Cold Rolling and Annealing

by Vladimir Torganchuk, Andrey Belyakov and Rustam Kaibyshev

Metals 2019, 9(7), 776; https://doi.org/10.3390/met9070776 - 11 Jul 2019

Cited by 8 | Viewed by 2610

Abstract

The microstructures and mechanical properties of Fe-0.4C-18Mn and Fe-0.6C-18Mn steels subjected to large strain cold rolling followed by annealing were studied. Cold rolling with a total reduction of 86% resulted in substantial strengthening at expense of plasticity. The yield strength and the ultimate [...] Read more.

The microstructures and mechanical properties of Fe-0.4C-18Mn and Fe-0.6C-18Mn steels subjected to large strain cold rolling followed by annealing were studied. Cold rolling with a total reduction of 86% resulted in substantial strengthening at expense of plasticity. The yield strength and the ultimate tensile strength of above 1400 MPa and 1600 MPa, respectively, were achieved in both steels, whereas total elongation decreased below 30%. Subsequent annealing at temperatures above 600 °C was accompanied with the development of recrystallization leading to fine-grained microstructures with an average grain size of about 1 μm in both steels. The fine-grained steels exhibited remarkable improved mechanical properties with a product of ultimate tensile strength by total elongation in the range of 50 to 70 GPa %. The fine-grained steel with relatively high carbon content of 0.6%C was characterized by ultimate tensile strength well above 1400 MPa that was remarkably higher than that of about 1200 MPa in the steel with 0.4%C. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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11 pages, 3238 KiB

Open AccessArticle

Computer-Aided Material Design for Crash Boxes Made of High Manganese Steels

by Angela Quadfasel, Marco Teller, Manjunatha Madivala, Christian Haase, Franz Roters and Gerhard Hirt

Metals 2019, 9(7), 772; https://doi.org/10.3390/met9070772 - 10 Jul 2019

Cited by 3 | Viewed by 4172

Abstract

During the last decades, high manganese steels (HMnS) were considered as promising materials for crash-relevant automobile components due to their extraordinary energy absorption capability in tensile tests. However, in the case of a crash, the specific energy, absorbed by folding of a crash [...] Read more.

During the last decades, high manganese steels (HMnS) were considered as promising materials for crash-relevant automobile components due to their extraordinary energy absorption capability in tensile tests. However, in the case of a crash, the specific energy, absorbed by folding of a crash box, is lower for HMnS as compared to the dual phase steel DP800. This behavior is related to the fact that the crash box hardly takes advantage of the high plastic formability of a recrystallized HMnS during deformation. It was revealed that with the help of an alternative heat treatment after cold rolling, the strength of HMnS could be increased for low strains to achieve a crash behavior comparable to DP800. In this work, a multi-scale finite element simulation approach was used to analyze the crash behavior of different material conditions of an HMnS. The crash behavior was evaluated under consideration of material efficiency and passenger safety criteria to identify the ideal material condition and sheet thickness for crash absorption by folding. The proposed simulation methodology reduces the experimental time and effort for crash box design. As a result of increasing material strength, the simulation exhibits a possible weight reduction of the crash box, due to thickness reduction, up to 35%. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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9 pages, 2167 KiB

Open AccessArticle

Processing Variants in Medium-Mn Steels

by John Speer, Radhakanta Rana, David Matlock, Alexandra Glover, Grant Thomas and Emmanuel De Moor

Metals 2019, 9(7), 771; https://doi.org/10.3390/met9070771 - 10 Jul 2019

Cited by 31 | Viewed by 4033

Abstract

This paper highlights some recent efforts to extend the use of medium-Mn steels for applications other than intercritically batch-annealed steels with exceptional ductility (and strengths in the range of about 1000 MPa). These steels are shown to enable a range of promising properties. [...] Read more.

This paper highlights some recent efforts to extend the use of medium-Mn steels for applications other than intercritically batch-annealed steels with exceptional ductility (and strengths in the range of about 1000 MPa). These steels are shown to enable a range of promising properties. In hot-stamping application concepts, elevated Mn concentration helps to stabilize austenite and to provide a range of attractive property combinations, and also reduces the processing temperatures and likely eliminates the need for press quenching. The “double soaking” concept also provides a wide range of attractive mechanical property combinations that may be applicable in cold-forming applications, and could be implemented in continuous annealing and/or continuous galvanizing processes where Zn-coating would typically represent an additional austempering step. Quenching and partitioning of steels with elevated Mn concentrations have exhibited very high strengths, with attractive tensile ductility; and medium-Mn steels have been successfully designed for quenching and partitioning using room temperature as the quench temperature, thereby effectively decoupling the quenching and partitioning steps. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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12 pages, 2613 KiB

Open AccessArticle

Deformation Behavior of a Double Soaked Medium Manganese Steel with Varied Martensite Strength

by Alexandra Glover, Paul J. Gibbs, Cheng Liu, Donald W. Brown, Bjørn Clausen, John G. Speer and Emmanuel De Moor

Metals 2019, 9(7), 761; https://doi.org/10.3390/met9070761 - 07 Jul 2019

Cited by 17 | Viewed by 3339

Abstract

The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite [...] Read more.

The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite strength and microstructural characteristics, which composed the bulk of the matrix phase, were characterized. It was found that the addition of either as-quenched or tempered athermal martensite led to an improvement in mechanical properties as compared to a ferrite plus austenite medium manganese steel, although the yielding and work hardening behavior were highly dependent upon the martensite characteristics. Specifically, athermal martensite was found to promote continuous yielding and improve the work hardening rate during deformation. The results of this study are particularly relevant when considering the effect of post-processing thermal heat treatments, such as tempering or elevated temperature service environments, on the mechanical properties of medium manganese steels containing athermal martensite. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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14 pages, 9557 KiB

Open AccessArticle

From High-Manganese Steels to Advanced High-Entropy Alloys

by Christian Haase and Luis Antonio Barrales-Mora

Metals 2019, 9(7), 726; https://doi.org/10.3390/met9070726 - 27 Jun 2019

Cited by 12 | Viewed by 4418

Abstract

Arguably, steels are the most important structural material, even to this day. Numerous design concepts have been developed to create and/or tailor new steels suited to the most varied applications. High-manganese steels (HMnS) stand out for their excellent mechanical properties and their capacity [...] Read more.

Arguably, steels are the most important structural material, even to this day. Numerous design concepts have been developed to create and/or tailor new steels suited to the most varied applications. High-manganese steels (HMnS) stand out for their excellent mechanical properties and their capacity to make use of a variety of physical mechanisms to tailor their microstructure, and thus their properties. With this in mind, in this contribution, we explore the possibility of extending the alloy design concepts that haven been used successfully in HMnS to the recently introduced high-entropy alloys (HEA). To this aim, one HMnS steel and the classical HEA Cantor alloy were subjected to cold rolling and heat treatment. The evolution of the microstructure and texture during the processing of the alloys and the resulting properties were characterized and studied. Based on these results, the physical mechanisms active in the investigated HMnS and HEA were identified and discussed. The results evidenced a substantial transferability of the design concepts and more importantly, they hint at a larger potential for microstructure and property tailoring in the HEA. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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13 pages, 3246 KiB

Open AccessArticle

Development of a Cr-Ni-V-N Medium Manganese Steel with Balanced Mechanical and Corrosion Properties

by Tarek Allam, Xiaofei Guo, Simon Sevsek, Marta Lipińska-Chwałek, Atef Hamada, Essam Ahmed and Wolfgang Bleck

Metals 2019, 9(6), 705; https://doi.org/10.3390/met9060705 - 22 Jun 2019

Cited by 27 | Viewed by 4153

Abstract

A novel medium manganese (MMn) steel with additions of Cr (18%), Ni (5%), V (1%), and N (0.3%) was developed in order to provide an enhanced corrosion resistance along with a superior strength–ductility balance. The laboratory melted ingots were hot rolled, cold rolled, [...] Read more.

A novel medium manganese (MMn) steel with additions of Cr (18%), Ni (5%), V (1%), and N (0.3%) was developed in order to provide an enhanced corrosion resistance along with a superior strength–ductility balance. The laboratory melted ingots were hot rolled, cold rolled, and finally annealed at 1000 °C for 3 min. The recrystallized single-phase austenitic microstructure consisted of ultrafine grains (~1.3 µm) with a substantial amount of Cr- and V-based precipitates in a bimodal particle size distribution (100–400 nm and <20 nm). The properties of the newly developed austenitic MMn steel X20CrNiMnVN18-5-10 were compared with the standard austenitic stainless steel X5CrNi18-8 and with the austenitic twinning-induced plasticity (TWIP) steel X60MnAl17-1. With a total elongation of 45%, the MMn steel showed an increase in yield strength by 300 MPa and in tensile strength by 150 MPa in comparison to both benchmark steels. No deformation twins were observed even after fracture for the MMn steel, which emphasizes the role of the grain size and precipitation-induced change in the austenite stability in controlling the deformation mechanism. The potentio-dynamic polarization measurements in 5% NaCl revealed a very low current density value of 7.2 × 10⁻⁴ mA/cm² compared to that of TWIP steel X60MnAl17-1 of 8.2 × 10⁻³ mA/cm², but it was relatively higher than that of stainless steel X5CrNi18-8 of 2.0 × 10⁻⁴ mA/cm². This work demonstrates that the enhanced mechanical properties of the developed MMn steel are tailored by maintaining an ultrafine grain microstructure with a significant amount of nanoprecipitates, while the high corrosion resistance in 5% NaCl solution is attributed to the high Cr and N contents as well as to the ultrafine grain size. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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9 pages, 3646 KiB

Open AccessArticle

Processing–Microstructure Relation of Deformed and Partitioned (D&P) Steels

by Li Liu, Binbin He and Mingxin Huang

Metals 2019, 9(6), 695; https://doi.org/10.3390/met9060695 - 20 Jun 2019

Cited by 6 | Viewed by 3147

Abstract

An ultrastrong and ductile deformed and partitioned (D&P) steel developed by dislocation engineering has been reported recently. However, the microstructure evolution during the D&P processes has not yet been fully understood. The present paper aims to elucidate the process–microstructure relation in D&P process. [...] Read more.

An ultrastrong and ductile deformed and partitioned (D&P) steel developed by dislocation engineering has been reported recently. However, the microstructure evolution during the D&P processes has not yet been fully understood. The present paper aims to elucidate the process–microstructure relation in D&P process. Specifically, the evolution of phase fraction and microstructure during the corresponding D&P process are captured by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Subsequently, the effect of partitioning temperature on dislocation density and mechanical properties of D&P steel is investigated with the assistance of uniaxial tensile tests and synchrotron X-ray diffraction. It is found that a heterogeneous microstructure is firstly realized by hot rolling. The warm rolling is crucial in introducing dislocations, while deformation-induced martensite is mainly formed during cold rolling. The dislocation density of the D&P steel gradually decreases with the increase of partitioning temperature, while the high yield strength is maintained owing to the bake hardening. The ductility is firstly enhanced while then deteriorated by increasing partitioning temperature due to the strong interaction between dislocation and interstitial atoms at higher partitioning temperatures. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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10 pages, 6084 KiB

Open AccessArticle

Austenite Reversion Tempering-Annealing of 4 wt.% Manganese Steels for Automotive Forging Application

by Alexander Gramlich, Robin Emmrich and Wolfgang Bleck

Metals 2019, 9(5), 575; https://doi.org/10.3390/met9050575 - 17 May 2019

Cited by 27 | Viewed by 4433

Abstract

New medium Mn steels for forged components, in combination with a new heat treatment, are presented. This new annealing process implies air-cooling after forging and austenite reversion tempering (AC + ART). This leads to energy saving compared to other heat treatments, like quenching [...] Read more.

New medium Mn steels for forged components, in combination with a new heat treatment, are presented. This new annealing process implies air-cooling after forging and austenite reversion tempering (AC + ART). This leads to energy saving compared to other heat treatments, like quenching and tempering (Q + T) or quenching and partitioning (Q + P). Furthermore, the temperature control of AC + ART is easy, which increases the applicability to forged products with large diameters. Laboratory melts distinguished by Ti, B, Mo contents have been casted and consecutively forged into semi-finished products. Mechanical properties and microstructure have been characterized for the AC and the AC + ART states. The as forged-state shows YS from 900 MPa to 1000 MPa, UTS from 1350 MPa to 1500 MPa and impact toughness from 15 J to 25 J. Through the formation of nanostructured retained metastable austenite an increase in impact toughness was achieved with values from 80 J to 100 J dependent on the chemical composition. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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24 pages, 16356 KiB

Open AccessFeature PaperArticle

Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels

by Manjunatha Madivala, Alexander Schwedt, Ulrich Prahl and Wolfgang Bleck

Metals 2019, 9(3), 367; https://doi.org/10.3390/met9030367 - 21 Mar 2019

Cited by 19 | Viewed by 5335

Abstract

The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m

^{2}

and 29 [...] Read more.

The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m

^{2}

and 29 mJ/m

^{2}

. The evolution of microstructure, deformation mechanisms and micro-cracks development with increasing deformation was analyzed. Al-addition has led to the decrease of C diffusivity and reduction in tendency for Mn-C short-range ordering resulting in the suppression of serrated flow caused due to dynamic strain aging (DSA) in an alloy with 0.3 wt.% C at room temperature and quasi-static testing, while DSA was delayed in an alloy with 0.6 wt.% C. However, an alloy with 0.6 wt.% C showing DSA effect exhibited enhanced strain hardening and ductility compared to an alloy with 0.3 wt.% C without DSA effect. Twinning was identified as the most predominant deformation mode in both the alloys, which occurred along with dislocation glide. Al-addition has increased SFE thereby delaying the nucleation of deformation twins and prolonged saturation of twinning, which resulted in micro-cracks initiation only just prior to necking or failure. The increased stress concentration caused by the interception of deformation twins or slip bands at grain boundaries (GB) has led to the development of micro-cracks mainly at GB and triple junctions. Deformation twins and slip bands played a vital role in assisting inter-granular crack initiation and propagation. Micro-cracks that developed at manganese sulfide and aluminum nitride inclusions showed no tendency for growth even after large deformation indicating the minimal detrimental effect on the tensile properties. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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20 pages, 16989 KiB

Open AccessFeature PaperArticle

Strain-Rate-Dependent Deformation Behavior and Mechanical Properties of a Multi-Phase Medium-Manganese Steel

by Simon Sevsek, Christian Haase and Wolfgang Bleck

Metals 2019, 9(3), 344; https://doi.org/10.3390/met9030344 - 18 Mar 2019

Cited by 35 | Viewed by 4911

Abstract

The strain-rate-dependent deformation behavior of an intercritically annealed X6MnAl12-3 medium-manganese steel was analyzed with respect to the mechanical properties, activation of deformation-induced martensitic phase transformation, and strain localization behavior. Intercritical annealing at 675 °C for 2 h led to an ultrafine-grained multi-phase microstructure [...] Read more.

The strain-rate-dependent deformation behavior of an intercritically annealed X6MnAl12-3 medium-manganese steel was analyzed with respect to the mechanical properties, activation of deformation-induced martensitic phase transformation, and strain localization behavior. Intercritical annealing at 675 °C for 2 h led to an ultrafine-grained multi-phase microstructure with 45% of mostly equiaxed, recrystallized austenite and 55% ferrite or recovered, lamellar martensite. In-situ digital image correlation methods during tensile tests revealed strain localization behavior during the discontinuous elastic-plastic transition, which was due to the localization of strain in the softer austenite in the early stages of plastic deformation. The dependence of the macroscopic mechanical properties on the strain rate is due to the strain-rate sensitivity of the microscopic deformation behavior. On the one hand, the deformation-induced phase transformation of austenite to martensite showed a clear strain-rate dependency and was partially suppressed at very low and very high strain rates. On the other hand, the strain-rate-dependent relative strength of ferrite and martensite compared to austenite influenced the strain partitioning during plastic deformation, and subsequently, the work-hardening rate. As a result, the tested X6MnAl12-3 medium-manganese steel showed a negative strain-rate sensitivity at very low to medium strain rates and a positive strain-rate sensitivity at medium to high strain rates. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)

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