Press hardening with manganese-boron steels is a prominent manufacturing technique that allows for reduced weight and expense in automotive construction,while providing enhanced crash performance.Nevertheless,the deve...Press hardening with manganese-boron steels is a prominent manufacturing technique that allows for reduced weight and expense in automotive construction,while providing enhanced crash performance.Nevertheless,the development of a loosely attached oxide layer during press hardening and following additional processing of the layer presents a significant risk to the dimensional precision of the completed product.Here,we develop a new preprocessing approach to address the scale spallation issue by introducing trace amounts of silicate and tungstate into the rinsing solution following pickling.We demonstrate that the pre-deposited membrane promotes the formation of a noticeably thinner,more continuous and stickier oxide scale at high temperatures,enabling the direct application of automobile painting onto the scale.Our research provides an economical remedy to the troublesome scale flaking issue without requiring any modifications to the existing production line,and conveys a thorough comprehension of the mechanism by which the preprocessed membrane resists high-temperature oxidation.展开更多
Microalloyed steels are extensively utilized in the automotive industry for their superior strength–toughness synergy.Structural components,such as cranks,wheels,and front axles,are subjected to fluctuating or repeti...Microalloyed steels are extensively utilized in the automotive industry for their superior strength–toughness synergy.Structural components,such as cranks,wheels,and front axles,are subjected to fluctuating or repetitive stresses during service,which cause fatigue damage or failure.Therefore,improving the fatigue properties of microalloyed steels is crucial to broaden their applications.An overview of the factors affecting the fatigue properties of microalloyed steels is provided,beginning with a concise description of microalloyed steels,followed by a discussion of key factors,such as microstructure,precipitation,and non-metallic inclusions,that influence fatigue performance.Strategies for enhancing fatigue properties are also explored,including non-metallic inclusion modification,surface treatment,and microstructure tailoring.Modification treatment of non-metallic inclusions can alter their morphology,size,quantity,distribution,etc.,thereby reducing the adverse effect on fatigue performance.The surface treatment enhances resistance to crack initiation by introducing compressive residual stress or refining the surface microstructure.Microstructure tailoring involves various heat treatment processes that can slow fatigue crack growth.Ultimately,the latest developments and future prospects of fatigue properties in microalloyed steels,based on academic research and industrial practices,are also summarized.展开更多
The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain leve...The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness.With increasing Ti content,the grain size in the steel decreased from 17.7 to 8.9μm.This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations,which act as barriers to hinder crack propagation.The Ti microalloyed steel exhibits a 20%increase in yield strength and a 14%increase in tensile strength.The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%.The low-temperature impact toughness of the steel gradually decreases with increasing Ti content.At low Ti content,the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions.At high Ti content,the low-temperature impact toughness of the steel deteriorates due to several factors.These include the narrower tough–brittle transition zone,grain boundary embrittlement caused by small-sized grains,and the decrease in the solid solution strengthening effect.展开更多
This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that ...This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.展开更多
In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The ...In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).展开更多
The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulati...The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.展开更多
Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDS...Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDSSs and HDSSs in recent years are reviewed in this paper.If proper heat input is provided,SDSSs and HDSSs can be welded with most fusion welding processes,while tungsten inert gas welding is the most popular process.SDSSs and HDSSs are more prone to secondary phases precipitation than the standard and lean grades,and heat input for SDSSs and HDSSs welding is restricted to a smaller range.Matching filler materials are usually recommended for SDSSs and HDSSs welding,rather than Ni-riched ones for standard and lean grades.Nitrogen addition in shielding gas is always beneficial.Post weld heat treatment with slow cooling rate will be harmful.Hot cracking tendency of SDSSs and HDSSs joints is not high,but sometimes they can suffer from hydrogen induced stress cracking.展开更多
A novel plasma torch nitriding technology was applied for the first time to improve the surface properties of M2 high-speed steel by adjusting different experimental parameters.The nitrogen content,precipitate,microst...A novel plasma torch nitriding technology was applied for the first time to improve the surface properties of M2 high-speed steel by adjusting different experimental parameters.The nitrogen content,precipitate,microstructure,mechanical property,and corrosion resistance of the nitrided layer were comprehensively analyzed using an ONH analyzer,scanning electron microscope(SEM),micro-area X-ray diffractometer,transmission electron microscope(TEM),Vickers microhardness tester,high-temperature wear tester,3D profilometer,tensile testing machine,and electrochemical workstation.The research results show that the novel plasma torch nitriding technology can achieve synergistic strengthening of nitrogen,carbon,and alloying element solid solution,precipitation strengthening,and martensitic structure on the surface of M2 high-speed steel.The nitrogen content on the specimen surface increased up to 0.17%,while the size and area of carbides were reduced by 89%and 86%,respectively,indicating a transformation towards fine nitrogen-rich precipitates.Compared to the original M2 steel,the nitrided specimens exhibited significant improvements in overall performance.The hardness increased from 228 HV_(0.2)to a maximum of 795 HV_(0.2),the wear coefficient decreased from a maximum of 0.8 to 0.49,the tensile strength increased from 753 MPa to a maximum of 934 MPa,and the corrosion current density decreased from 1.2×10^(−5)to a minimum of 1.9×10^(−6)A/cm^(2).展开更多
High-temperature confocal laser scanning microscopy(HT-CLSM)is considered as a powerful tool for in situ observation of the phase transformation of steels at elevated temperatures.It breaks the limitation that convent...High-temperature confocal laser scanning microscopy(HT-CLSM)is considered as a powerful tool for in situ observation of the phase transformation of steels at elevated temperatures.It breaks the limitation that conventional approaches on this aspect can only post-mortem the microstructure at room temperature.The working principle and major functions of HT-CLSM in initial are introduced and the utilization in details with HT-CLSM is summarized,including the behaviors of melting-solidifying,austenite reversion,as well as the austenite decomposition(formation of Widmanstätten,pearlite,acicular ferrite,bainite and martensite)in steels.Moreover,a serie of HT-CLSM images are used to explore the growth kinetic of phase at elevated temperatures with additional theoretical calculation models.Finally,the in situ HT-CLSM observations of phase transformation,combined with post-mortem electron backscatter diffraction analysis,is also summarized to elucidate the crystallographic evolution.展开更多
The corrosion performance of oxide dispersion strengthened(ODS)steel is crucial for SCWR application.Machine learning(ML)models were established to predict the mass gain of ODS steels under corrosion conditions(i.e.,s...The corrosion performance of oxide dispersion strengthened(ODS)steel is crucial for SCWR application.Machine learning(ML)models were established to predict the mass gain of ODS steels under corrosion conditions(i.e.,supercritical water),thereby evaluating their corrosion resistance.The grain and particle morphologies and crystal and interface structures of nanoparticles of six ODS steels were studied by transmission electron microscopy,scanning transmission electron microscopy,and high-resolution transmission electron microscopy.Among six ML models employed,the LightGBM(LGBM)model shows the highest accuracy(root mean square error of 43.18 mg/dm^(2) and 50.21 mg/dm^(2),mean absolute error of 25.91 mg/dm^(2) and 27.82 mg/dm^(2),and coefficient of determination R^(2) of 0.97 and 0.96 for training set and testing set,respectively)in predicting the mass gain of ODS steels.The LGBM feature importance coefficients were also applied to denote the degree of the feature on corrosion resistance.For microstructural features,the parameters that greatly influence corrosion resistance are inter-particle spacing and grain diameter,with importance scores of 73 and 63,respectively.Moreover,there is a strong synergistic influence between Cr and Al on the corrosion resistance of ODS steels.Developing this efficient and accurate LGBM model not only enhances the understanding of ODS steel corrosion mechanisms but also provides valuable insights for the targeted optimization and design of high-performance ODS alloys.展开更多
The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction...The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction,transmission electron microscopy,hardness and tensile tests.Alloying with Mo in the steels promotes the precipitation of Mo_(2)C carbides while inhibits the precipitation ofκ-carbides.The addition of Mo exceeding 2.5 wt.%facilitates the precipitation of intragranular Mo_(2)C carbides,whereas with up to 2.5 wt.%Mo,only intergranular Mo_(2)C carbides precipitate.With containing more Mo in the steels,the strength increases due to enhancement of precipitation strengthening and solid solution strengthening,while ductility gradually decreases.3Mo steel exhibits excellent overall mechanical properties,with the synergistic increase in strength,ductility,and work-hardening rate,which can be attributed to the precipitation of fine intragranular Mo_(2)C distributed uniformly in the matrix and the suppression of the formation of coarsenedκ-carbides.However,in 3.5Mo steel,abundant coarsened Mo2C precipitation strongly interacts with dislocations to promote crack propagation along non-coherent interfaces,leading to a high initial work-hardening rate but severe ductility loss.展开更多
Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increase...Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increased when the initial aluminum content increased from 0.76 to 3.85 wt.%.Utilizing the two-film theory,a steel–flux reaction kinetic model controlled by mass transfer was established,which considered the influence of the initial composition on the density of liquid steel and flux.The mass transfer of aluminum in the steel phase was the reaction rate-determining step.It was confirmed that the mass transfer coefficient of Al was 1.87×10^(−4).The predicted results of the kinetic model were consistent and reliable with the experimental results.Thermodynamic equilibrium calculation was performed using FactSage 8.2,which was compared with the steel and flux final composition after 30 min.The content of initial aluminum in the liquid steel played a critical role in the SiO_(2)equilibrium content of the mold flux.In addition,the steel–flux reaction between[Al]and(SiO_(2))occurred with the initial SiO_(2)content in the mold flux lower than 3 wt.%.展开更多
The microstructural evolution,mechanical properties,and wear behavior of medium manganese steels(MMSs)with varying aluminum(Al)contents were investigated.It was observed that the microstructure of MMS transferred from...The microstructural evolution,mechanical properties,and wear behavior of medium manganese steels(MMSs)with varying aluminum(Al)contents were investigated.It was observed that the microstructure of MMS transferred from a predominantly martensitic phase(in the Al-free state)to a ferrite/martensite or ferrite/austenite duplex structure with increasing Al content.The hardness of MMS decreased with Al addition,while the impact absorbed energy and yield strength were optimized in 2%Al-containing variant.Frictional wear tests demonstrated that 2 wt.%Al-MMS exhibited superior wear resistance due to the twinning-induced plasticity effect.Conversely,under impact abrasion wear conditions,the Al-free MMS displayed the lowest mass loss,attributing to high surface hardness and remarkable work hardening capacity.These findings indicates that Al content-tailored MMSs can be selectively applied in different wear environments,with 2 wt.%Al-MMS being optimal for static load conditions and the Al-free MMS for dynamic impact abrasion scenarios.展开更多
Cryogenic steels,i.e.,steels with maximum toughness at particularly low temperature,are increasingly becoming the focus of research.Cryogenic steels are usually alloyed with 5%–9%nickel.Ni can also be substituted by ...Cryogenic steels,i.e.,steels with maximum toughness at particularly low temperature,are increasingly becoming the focus of research.Cryogenic steels are usually alloyed with 5%–9%nickel.Ni can also be substituted by manganese as an austenite former.These high-manganese cryogenic grades are a cost-effective alternative to nickel-alloyed steels for use in liquefied natural gas storage tanks.The Mn content can then be more than 20 wt.%and lead to problems in production,particularly in the continuous casting process.In continuous casting of high-Mn-grades,quality issues and even breakout may result from the initial solidification behavior of the steel grades at high temperatures.Hot cracks form when a critical load is exceeded during solidification,close to the solidus temperature of the steel.A selected high-Mn-steel grade was characterized with respect to liquidus and solidus temperatures by means of thermal analysis and computational thermodynamics.In addition,so-called submerged split chill tensile tests were carried out to further understand the crack sensitivity of the solidifying shell for high-manganese cryogenic steels.The results reveal the presence of coarse hot tears,and also,a high frequency of hot cracks was observed at the location with the maximum accumulated strain,which is in line with the applied cracking criterion of Pierer and Bernhard for this investigation.In summary,the initial solidification phase of continuous casting poses a high risk of cracking for high-manganese cryogenic steel.展开更多
In this work,tensile mechanical behavior of 316L steels fabricated by three different processing methods(casting,powder extrusion printing(PEP)and laser powder bed fusion(LPBF))was studied in the presence of liquid le...In this work,tensile mechanical behavior of 316L steels fabricated by three different processing methods(casting,powder extrusion printing(PEP)and laser powder bed fusion(LPBF))was studied in the presence of liquid lead-bismuth eutectic(LBE)and air at 350℃.The results show that all three steels tested in LBE are not subjected to evident degradation of tensile elongation to failure and strength compared to those tested in air,suggesting that LME does not occur regardless of the processing methods.The LPBF 316L steel exhibits the highest yield strength(420-435 MPa),followed by casting 316 L(~242 MPa)and PEP 316L(146-165 MPa).Ultimate tensile strength of three steels is comparable and ranges from 427 to 485 MPa.The PEP and casting 316L steels have similar total elongation to failure(i.e.,40.0%-43.8%),whereas this property decreases markedly to 18.6%-19.5% for the LPBF 316 L steel.The superior strength and relatively low ductility of the LPBF 316L steel can be attributed to nanosized dislocations trapped at cell structures which can produce a remarkable strengthening effect to the steel matrix.By contrast,due to massive residual micropores,the PEP 316L steel has the lowest strength.展开更多
Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te tr...Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te treatment,MnTe precipitation is unexpected.The critical precipitation behavior of MnTe inclusions was investigated through scanning electron microscopy,transmission electron microscopy,machine learning,and first-principles calculation.MnTe preferentially precipitated at the container mouth for sphere-like sulfides and at the interface between MnS grain boundaries and steel matrix for rod-like sulfides.The MnS/MnTe interface was semicoherent.A composition transition zone with a rock-salt structure exhibiting periodic changes existed to maintain the semicoherent interface.The critical precipitation behavior of MnTe inclusions in resulfurized steels involved three stages at varying temperatures.First,Mn(S,Te)precipitated during solidification.Second,MnTe with a rock-salt structure precipitated from Mn(S,Te).Third,MnTe with a hexagonal NiAs structure transformed from the rock-salt structure.The solubility of Te in MnS decreased with decreasing temperature.The critical precipitation behavior of MnTe inclusions in resulfurized steels was related to the MnS precipitation temperature.With the increase in MnS precipitation temperature,the critical Te/S weight ratio decreased.In consideration of the cost-effectiveness of Te addition for industrial production,the Te content in resulfurized steels should be controlled in accordance with MnS precipitation temperature and S content.展开更多
The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compare...The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.展开更多
Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most suscepti...Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most susceptible sites for pitting,and have therefore garnered significant attention.This review critically ex-amines the issue of how inclusions induce pitting,with a particular focus on three mechanisms:sponta-neous dissolution of inclusions,active dissolution of Cr-depleted regions,and propagation of microcracks at the inclusion-matrix interface.While researchers have made significant strides in understanding these mechanisms over the past few decades,many gaps and controversies remain.Details such as the ini-tial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study.Moreover,some old concepts and methods need to be revised to arrive at more credible conclusions.This review aims to delve deeply into these important issues and provide inspiration for future research.展开更多
This work constructed a machine learning(ML)model to predict the atmospheric corrosion rate of low-alloy steels(LAS).The material properties of LAS,environmental factors,and exposure time were used as the input,while ...This work constructed a machine learning(ML)model to predict the atmospheric corrosion rate of low-alloy steels(LAS).The material properties of LAS,environmental factors,and exposure time were used as the input,while the corrosion rate as the output.6 dif-ferent ML algorithms were used to construct the proposed model.Through optimization and filtering,the eXtreme gradient boosting(XG-Boost)model exhibited good corrosion rate prediction accuracy.The features of material properties were then transformed into atomic and physical features using the proposed property transformation approach,and the dominant descriptors that affected the corrosion rate were filtered using the recursive feature elimination(RFE)as well as XGBoost methods.The established ML models exhibited better predic-tion performance and generalization ability via property transformation descriptors.In addition,the SHapley additive exPlanations(SHAP)method was applied to analyze the relationship between the descriptors and corrosion rate.The results showed that the property transformation model could effectively help with analyzing the corrosion behavior,thereby significantly improving the generalization ability of corrosion rate prediction models.展开更多
Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years...Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.展开更多
基金supported by the Liaoning Youth Science Foundation Project B Category(Contract No.2025010041-JH6/1010)the National Natural Science Foundation of China(Grant No.52471103).
文摘Press hardening with manganese-boron steels is a prominent manufacturing technique that allows for reduced weight and expense in automotive construction,while providing enhanced crash performance.Nevertheless,the development of a loosely attached oxide layer during press hardening and following additional processing of the layer presents a significant risk to the dimensional precision of the completed product.Here,we develop a new preprocessing approach to address the scale spallation issue by introducing trace amounts of silicate and tungstate into the rinsing solution following pickling.We demonstrate that the pre-deposited membrane promotes the formation of a noticeably thinner,more continuous and stickier oxide scale at high temperatures,enabling the direct application of automobile painting onto the scale.Our research provides an economical remedy to the troublesome scale flaking issue without requiring any modifications to the existing production line,and conveys a thorough comprehension of the mechanism by which the preprocessed membrane resists high-temperature oxidation.
基金financially supported by the National Key R&D Program of China(No.2021YFB3702403)financial support from the National Natural Science Foundation of China(Nos.52122408 and 52071023)。
文摘Microalloyed steels are extensively utilized in the automotive industry for their superior strength–toughness synergy.Structural components,such as cranks,wheels,and front axles,are subjected to fluctuating or repetitive stresses during service,which cause fatigue damage or failure.Therefore,improving the fatigue properties of microalloyed steels is crucial to broaden their applications.An overview of the factors affecting the fatigue properties of microalloyed steels is provided,beginning with a concise description of microalloyed steels,followed by a discussion of key factors,such as microstructure,precipitation,and non-metallic inclusions,that influence fatigue performance.Strategies for enhancing fatigue properties are also explored,including non-metallic inclusion modification,surface treatment,and microstructure tailoring.Modification treatment of non-metallic inclusions can alter their morphology,size,quantity,distribution,etc.,thereby reducing the adverse effect on fatigue performance.The surface treatment enhances resistance to crack initiation by introducing compressive residual stress or refining the surface microstructure.Microstructure tailoring involves various heat treatment processes that can slow fatigue crack growth.Ultimately,the latest developments and future prospects of fatigue properties in microalloyed steels,based on academic research and industrial practices,are also summarized.
基金supported by the National Natural Science Foundation of China(Nos.52174311 and 51974020).
文摘The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness.With increasing Ti content,the grain size in the steel decreased from 17.7 to 8.9μm.This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations,which act as barriers to hinder crack propagation.The Ti microalloyed steel exhibits a 20%increase in yield strength and a 14%increase in tensile strength.The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%.The low-temperature impact toughness of the steel gradually decreases with increasing Ti content.At low Ti content,the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions.At high Ti content,the low-temperature impact toughness of the steel deteriorates due to several factors.These include the narrower tough–brittle transition zone,grain boundary embrittlement caused by small-sized grains,and the decrease in the solid solution strengthening effect.
基金supported by the National Natural Science Foundation of China(No.52271089)the financial support from the C hina Postdoctoral Science Foundation(No.2023M732192)。
文摘This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
基金support of the Research Project Supported by Shanxi Scholarship Council of China(2022-040)"Chunhui Plan"Collaborative Research Project by the Ministry of Education of China(HZKY20220507)+2 种基金National Natural Science Foundation of China(52104338)Applied Fundamental Research Programs of Shanxi Province(202303021221036)Shandong Postdoctoral Science Foundation(SDCX-ZG-202303027,SDBX2023054).
文摘In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).
基金financial support from the National Natural Science Foundation of China(Nos.52233018 and 51831002)the China Baowu Low Carbon Metallurgy Innovation Foudation(No.BWLCF202213)。
文摘The influence of Nb-V microalloying on the hot deformation behavior and microstructures of medium Mn steel(MMS)was investigated by uniaxial hot compression tests.By establishing the constitutive equations for simulating the measured flow curves,we successfully constructed deformation activation energy(Q)maps and processing maps for identifying the region of flow instability.We concluded the following consequences of Nb-V alloying for MMS.(i)The critical strain increases and the increment diminishes with the increasing deformation temperature,suggesting that NbC precipitates more efficiently retard dynamic recrystallization(DRX)in MMS compared with solute Nb.(ii)The deformation activation energy of MMS is significantly increased and even higher than that of some reported high Mn steels,suggesting that its ability to retard DRX is greater than that of the high Mn content.(iii)The hot workability of MMS is improved by narrowing the hot processing window for the unstable flow stress,in which fine recrystallized and coarse unrecrystallized grains are present.
文摘Super duplex stainless steels(SDSSs)and hyper duplex stainless steels(HDSSs),with more alloying elements content,are more corrosion resistant than the standard grades.Progresses of research works on weldability of SDSSs and HDSSs in recent years are reviewed in this paper.If proper heat input is provided,SDSSs and HDSSs can be welded with most fusion welding processes,while tungsten inert gas welding is the most popular process.SDSSs and HDSSs are more prone to secondary phases precipitation than the standard and lean grades,and heat input for SDSSs and HDSSs welding is restricted to a smaller range.Matching filler materials are usually recommended for SDSSs and HDSSs welding,rather than Ni-riched ones for standard and lean grades.Nitrogen addition in shielding gas is always beneficial.Post weld heat treatment with slow cooling rate will be harmful.Hot cracking tendency of SDSSs and HDSSs joints is not high,but sometimes they can suffer from hydrogen induced stress cracking.
基金supported by the National Science and Technology Major Project of China(No.HT-J2019-V-0023-0140)Open Project of State Key Laboratory of Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(No.SKLASS 2023-03)the Science and Technology Commission of Shanghai Municipality(No.20511107700).
文摘A novel plasma torch nitriding technology was applied for the first time to improve the surface properties of M2 high-speed steel by adjusting different experimental parameters.The nitrogen content,precipitate,microstructure,mechanical property,and corrosion resistance of the nitrided layer were comprehensively analyzed using an ONH analyzer,scanning electron microscope(SEM),micro-area X-ray diffractometer,transmission electron microscope(TEM),Vickers microhardness tester,high-temperature wear tester,3D profilometer,tensile testing machine,and electrochemical workstation.The research results show that the novel plasma torch nitriding technology can achieve synergistic strengthening of nitrogen,carbon,and alloying element solid solution,precipitation strengthening,and martensitic structure on the surface of M2 high-speed steel.The nitrogen content on the specimen surface increased up to 0.17%,while the size and area of carbides were reduced by 89%and 86%,respectively,indicating a transformation towards fine nitrogen-rich precipitates.Compared to the original M2 steel,the nitrided specimens exhibited significant improvements in overall performance.The hardness increased from 228 HV_(0.2)to a maximum of 795 HV_(0.2),the wear coefficient decreased from a maximum of 0.8 to 0.49,the tensile strength increased from 753 MPa to a maximum of 934 MPa,and the corrosion current density decreased from 1.2×10^(−5)to a minimum of 1.9×10^(−6)A/cm^(2).
基金support received from the National Natural Science Foundation of China(52274305,U20A20277)the Hubei Province key research and development project(2022BAA021).
文摘High-temperature confocal laser scanning microscopy(HT-CLSM)is considered as a powerful tool for in situ observation of the phase transformation of steels at elevated temperatures.It breaks the limitation that conventional approaches on this aspect can only post-mortem the microstructure at room temperature.The working principle and major functions of HT-CLSM in initial are introduced and the utilization in details with HT-CLSM is summarized,including the behaviors of melting-solidifying,austenite reversion,as well as the austenite decomposition(formation of Widmanstätten,pearlite,acicular ferrite,bainite and martensite)in steels.Moreover,a serie of HT-CLSM images are used to explore the growth kinetic of phase at elevated temperatures with additional theoretical calculation models.Finally,the in situ HT-CLSM observations of phase transformation,combined with post-mortem electron backscatter diffraction analysis,is also summarized to elucidate the crystallographic evolution.
基金sponsored by the National Natural Science Foundation of China(Grants Nos.52171004,52471066,and 51871034).
文摘The corrosion performance of oxide dispersion strengthened(ODS)steel is crucial for SCWR application.Machine learning(ML)models were established to predict the mass gain of ODS steels under corrosion conditions(i.e.,supercritical water),thereby evaluating their corrosion resistance.The grain and particle morphologies and crystal and interface structures of nanoparticles of six ODS steels were studied by transmission electron microscopy,scanning transmission electron microscopy,and high-resolution transmission electron microscopy.Among six ML models employed,the LightGBM(LGBM)model shows the highest accuracy(root mean square error of 43.18 mg/dm^(2) and 50.21 mg/dm^(2),mean absolute error of 25.91 mg/dm^(2) and 27.82 mg/dm^(2),and coefficient of determination R^(2) of 0.97 and 0.96 for training set and testing set,respectively)in predicting the mass gain of ODS steels.The LGBM feature importance coefficients were also applied to denote the degree of the feature on corrosion resistance.For microstructural features,the parameters that greatly influence corrosion resistance are inter-particle spacing and grain diameter,with importance scores of 73 and 63,respectively.Moreover,there is a strong synergistic influence between Cr and Al on the corrosion resistance of ODS steels.Developing this efficient and accurate LGBM model not only enhances the understanding of ODS steel corrosion mechanisms but also provides valuable insights for the targeted optimization and design of high-performance ODS alloys.
基金supported by the funding of National Science and Technology Major Project,China(J2019-VI-0019-0134).
文摘The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%)Mo lightweight austenitic steels after annealing at 700℃was investigated by electron backscatter diffraction,transmission electron microscopy,hardness and tensile tests.Alloying with Mo in the steels promotes the precipitation of Mo_(2)C carbides while inhibits the precipitation ofκ-carbides.The addition of Mo exceeding 2.5 wt.%facilitates the precipitation of intragranular Mo_(2)C carbides,whereas with up to 2.5 wt.%Mo,only intergranular Mo_(2)C carbides precipitate.With containing more Mo in the steels,the strength increases due to enhancement of precipitation strengthening and solid solution strengthening,while ductility gradually decreases.3Mo steel exhibits excellent overall mechanical properties,with the synergistic increase in strength,ductility,and work-hardening rate,which can be attributed to the precipitation of fine intragranular Mo_(2)C distributed uniformly in the matrix and the suppression of the formation of coarsenedκ-carbides.However,in 3.5Mo steel,abundant coarsened Mo2C precipitation strongly interacts with dislocations to promote crack propagation along non-coherent interfaces,leading to a high initial work-hardening rate but severe ductility loss.
基金support from the National Key R&D Program of China(No.2023YFB3709900)the National Natural Science Foundation of China(Grant No.U22A20171).
文摘Steel–flux reactions involving the high aluminum(0.75–3.85 wt.%Al)low manganese(2.2 wt.%Mn)steel and the 18 wt.%SiO_(2)–18 wt.%Al2O3 mold flux were investigated.The results indicated that the reaction rate increased when the initial aluminum content increased from 0.76 to 3.85 wt.%.Utilizing the two-film theory,a steel–flux reaction kinetic model controlled by mass transfer was established,which considered the influence of the initial composition on the density of liquid steel and flux.The mass transfer of aluminum in the steel phase was the reaction rate-determining step.It was confirmed that the mass transfer coefficient of Al was 1.87×10^(−4).The predicted results of the kinetic model were consistent and reliable with the experimental results.Thermodynamic equilibrium calculation was performed using FactSage 8.2,which was compared with the steel and flux final composition after 30 min.The content of initial aluminum in the liquid steel played a critical role in the SiO_(2)equilibrium content of the mold flux.In addition,the steel–flux reaction between[Al]and(SiO_(2))occurred with the initial SiO_(2)content in the mold flux lower than 3 wt.%.
基金supported by the Guangxi Major Science and Technology Project(AB24010120)Young Talent Support Project of Guangzhou Association for Science and Technology(QT-2024-047)+3 种基金Key-Area Research and Development Program of Jiangxi Province(20243BBG71023)GDAS'Project of Science and Technology Development(2023GDASQNRC-0205 and 2024GDASZH-2024010102)Evaluation Project of Guangdong Provincial Key Laboratory(2023B1212060043)Young Elite Scientists Sponsorship Program by CAST(2022QNRC001).
文摘The microstructural evolution,mechanical properties,and wear behavior of medium manganese steels(MMSs)with varying aluminum(Al)contents were investigated.It was observed that the microstructure of MMS transferred from a predominantly martensitic phase(in the Al-free state)to a ferrite/martensite or ferrite/austenite duplex structure with increasing Al content.The hardness of MMS decreased with Al addition,while the impact absorbed energy and yield strength were optimized in 2%Al-containing variant.Frictional wear tests demonstrated that 2 wt.%Al-MMS exhibited superior wear resistance due to the twinning-induced plasticity effect.Conversely,under impact abrasion wear conditions,the Al-free MMS displayed the lowest mass loss,attributing to high surface hardness and remarkable work hardening capacity.These findings indicates that Al content-tailored MMSs can be selectively applied in different wear environments,with 2 wt.%Al-MMS being optimal for static load conditions and the Al-free MMS for dynamic impact abrasion scenarios.
基金supported by National Natural Science Foundation of China(Grant Nos.52174324,51974213 and 52204351)the China Postdoctoral Science Foundation(2022M722487)+1 种基金Open fund project(Grant No.FMRUlab23-05)supported by Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Educationsupport under the scope of the COMET program within the K2 Center“Integrated Computational Material,Process and Product Engineering(IC-MPPE)”(Project No.886385).
文摘Cryogenic steels,i.e.,steels with maximum toughness at particularly low temperature,are increasingly becoming the focus of research.Cryogenic steels are usually alloyed with 5%–9%nickel.Ni can also be substituted by manganese as an austenite former.These high-manganese cryogenic grades are a cost-effective alternative to nickel-alloyed steels for use in liquefied natural gas storage tanks.The Mn content can then be more than 20 wt.%and lead to problems in production,particularly in the continuous casting process.In continuous casting of high-Mn-grades,quality issues and even breakout may result from the initial solidification behavior of the steel grades at high temperatures.Hot cracks form when a critical load is exceeded during solidification,close to the solidus temperature of the steel.A selected high-Mn-steel grade was characterized with respect to liquidus and solidus temperatures by means of thermal analysis and computational thermodynamics.In addition,so-called submerged split chill tensile tests were carried out to further understand the crack sensitivity of the solidifying shell for high-manganese cryogenic steels.The results reveal the presence of coarse hot tears,and also,a high frequency of hot cracks was observed at the location with the maximum accumulated strain,which is in line with the applied cracking criterion of Pierer and Bernhard for this investigation.In summary,the initial solidification phase of continuous casting poses a high risk of cracking for high-manganese cryogenic steel.
基金Project(2024YFB4608600)supported by the National Key Research and Development Program of ChinaProjects(52271063,U21B2066,U24B2024)supported by the National Natural Science Foundation of China+3 种基金Project(JSGG20210713091539014)supported by the Shenzhen Science and Technology Innovation Commission Key Technical Project,ChinaProject(HNGD2025040)supported by the Overseas High-Level Talents Introduction of Henan Province,ChinaProject(240621041)supported by the Fundamental Research Funds of Henan Academy of Sciences,ChinaProject(20231120233925001)supported by Stabilization Support Program for Higher Education Institutions of Shenzhen,China。
文摘In this work,tensile mechanical behavior of 316L steels fabricated by three different processing methods(casting,powder extrusion printing(PEP)and laser powder bed fusion(LPBF))was studied in the presence of liquid lead-bismuth eutectic(LBE)and air at 350℃.The results show that all three steels tested in LBE are not subjected to evident degradation of tensile elongation to failure and strength compared to those tested in air,suggesting that LME does not occur regardless of the processing methods.The LPBF 316L steel exhibits the highest yield strength(420-435 MPa),followed by casting 316 L(~242 MPa)and PEP 316L(146-165 MPa).Ultimate tensile strength of three steels is comparable and ranges from 427 to 485 MPa.The PEP and casting 316L steels have similar total elongation to failure(i.e.,40.0%-43.8%),whereas this property decreases markedly to 18.6%-19.5% for the LPBF 316 L steel.The superior strength and relatively low ductility of the LPBF 316L steel can be attributed to nanosized dislocations trapped at cell structures which can produce a remarkable strengthening effect to the steel matrix.By contrast,due to massive residual micropores,the PEP 316L steel has the lowest strength.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52104335,51874195 and 52074179)the Shanghai“Super Postdoctoral”Incentive Plan(No.2020194).
文摘Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te treatment,MnTe precipitation is unexpected.The critical precipitation behavior of MnTe inclusions was investigated through scanning electron microscopy,transmission electron microscopy,machine learning,and first-principles calculation.MnTe preferentially precipitated at the container mouth for sphere-like sulfides and at the interface between MnS grain boundaries and steel matrix for rod-like sulfides.The MnS/MnTe interface was semicoherent.A composition transition zone with a rock-salt structure exhibiting periodic changes existed to maintain the semicoherent interface.The critical precipitation behavior of MnTe inclusions in resulfurized steels involved three stages at varying temperatures.First,Mn(S,Te)precipitated during solidification.Second,MnTe with a rock-salt structure precipitated from Mn(S,Te).Third,MnTe with a hexagonal NiAs structure transformed from the rock-salt structure.The solubility of Te in MnS decreased with decreasing temperature.The critical precipitation behavior of MnTe inclusions in resulfurized steels was related to the MnS precipitation temperature.With the increase in MnS precipitation temperature,the critical Te/S weight ratio decreased.In consideration of the cost-effectiveness of Te addition for industrial production,the Te content in resulfurized steels should be controlled in accordance with MnS precipitation temperature and S content.
基金Saeed Sadeghpour would like to thank Jane,Aatos Erkon säätiö(JAES),and Tiina ja Antti Herlinin säätiö(TAHS)for their financial support on Advanced Steels for Green Planet Project.The authors would also like to greatly thank the members of the“Formability Laboratory”and“Advanced Steels and Thermomechanically Processed Engineering Ma-terials Laboratory”for their help and support。
文摘The effects of deformation temperature on the transformation-induced plasticity(TRIP)-aided 304L,twinning-induced plasti-city(TWIP)-assisted 316L,and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechan-ical properties,strengthening mechanisms,and strength-ductility synergy.For this purpose,the scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),tensile testing,work-hardening analysis,and thermodynamics calcu-lations were used.The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels.As the deformation temperature increased,the metastable 304L stainless steel showed the sequence of TRIP,TWIP,and weakening of the induced plasticity mechanism;while the disappearance of the TWIP effect in the 316L stainless steel was also observed.However,the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temper-ature range,surpassing the performance of 304L and 316L stainless steels.In this regard,the dependency of the total elongation on the de-formation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms.These results re-vealed the importance of solid-solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.
基金supported by The National Natural Science Foundation of China(Nos.52271053 and 52271096)'the Shanghai Rising-Star Program(No.23QA1400500)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most susceptible sites for pitting,and have therefore garnered significant attention.This review critically ex-amines the issue of how inclusions induce pitting,with a particular focus on three mechanisms:sponta-neous dissolution of inclusions,active dissolution of Cr-depleted regions,and propagation of microcracks at the inclusion-matrix interface.While researchers have made significant strides in understanding these mechanisms over the past few decades,many gaps and controversies remain.Details such as the ini-tial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study.Moreover,some old concepts and methods need to be revised to arrive at more credible conclusions.This review aims to delve deeply into these important issues and provide inspiration for future research.
基金the National Key R&D Program of China(No.2021YFB3701705).
文摘This work constructed a machine learning(ML)model to predict the atmospheric corrosion rate of low-alloy steels(LAS).The material properties of LAS,environmental factors,and exposure time were used as the input,while the corrosion rate as the output.6 dif-ferent ML algorithms were used to construct the proposed model.Through optimization and filtering,the eXtreme gradient boosting(XG-Boost)model exhibited good corrosion rate prediction accuracy.The features of material properties were then transformed into atomic and physical features using the proposed property transformation approach,and the dominant descriptors that affected the corrosion rate were filtered using the recursive feature elimination(RFE)as well as XGBoost methods.The established ML models exhibited better predic-tion performance and generalization ability via property transformation descriptors.In addition,the SHapley additive exPlanations(SHAP)method was applied to analyze the relationship between the descriptors and corrosion rate.The results showed that the property transformation model could effectively help with analyzing the corrosion behavior,thereby significantly improving the generalization ability of corrosion rate prediction models.
基金support from the National Natural Science Foundation of China(Nos.51831002,51904028,and 52233018)the Beijing Municipal Natural Science Foundation(No.2242048)the Fundamental Research Funds for the Central Universities,China(No.FRF-EYIT-23-08).
文摘Plastic instability,including both the discontinuous yielding and stress serrations,has been frequently observed during the tensile deformation of medium-Mn steels(MMnS)and has been intensively studied in recent years.Unfortunately,research results are controversial,and no consensus has been achieved regarding the topic.Here,we first summarize all the possible factors that affect the yielding and flow stress serrations in MMnS,including the morphology and stability of austenite,the feature of the phase interface,and the deformation parameters.Then,we propose a universal mechanism to explain the conflicting experimental results.We conclude that the discontinuous yielding can be attributed to the lack of mobile dislocation before deformation and the rapid dislocation multiplication at the beginning of plastic deformation.Meanwhile,the results show that the stress serrations are formed due to the pinning and depinning between dislocations and interstitial atoms in austenite.Strain-induced martensitic transformation,influenced by the mechanical stability of austenite grain and deformation parameters,should not be the intrinsic cause of plastic instability.However,it can intensify or weaken the discontinuous yielding and the stress serrations by affecting the mobility and density of dislocations,as well as the interaction between the interstitial atoms and dislocations in austenite grains.
