The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerge...The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.展开更多
The low damage resistance and fracture toughness hinder the widespread application of ultrahighstrength dual phase(DP)steels.In this work,we propose a novel strategy to improve the fracture toughness of ultrahigh-stre...The low damage resistance and fracture toughness hinder the widespread application of ultrahighstrength dual phase(DP)steels.In this work,we propose a novel strategy to improve the fracture toughness of ultrahigh-strength DP steels by an order of magnitude without sacrificing the tensile strength.Six ultrahigh-strength DP steels with varying microstructure but comparable tensile strength(>1400 MPa)were prepared via tailoring the heat treatment process after cold rolling.Additionally,finite element(FE)method incorporated with Gurson-Tvergaad-Needleman(GTN)model and cohesive zone model(CZM)is established to simulate the fracture behavior of DP steel.Twelve model DP steels with different ferrite sizes and F/M strength differences are constructed.The combined experiment and simulation results demonstrate that(i)ferrite/martensite(F/M)interface decohesion prevails in all steels,(ii)the ferrite morphology has a strong influence on the fracture toughness of ultrahigh-strength DP steels,(iii)the effects of matrix type,ferrite size,and F/M hardness difference on the fracture toughness are relatively weak,(iv)the exceptional high fracture toughness of plate-like DP steel can be attributed to the crack deflection,crack divider and crack arrester mechanisms induced by F/M interface decohesion.展开更多
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
A series of high-strength wind power steels with various microstructural morphologies was produced by hot-rolled and thermo-mechanical controlled processes.The microstructure,microhardness,and tensile behavior observe...A series of high-strength wind power steels with various microstructural morphologies was produced by hot-rolled and thermo-mechanical controlled processes.The microstructure,microhardness,and tensile behavior observed using in-situ techniques in various types of steels were investigated.The experimental results demonstrated that the 3 microstructural morphologies(band-,net-,and fiber-structures)can be clarified and categorized;each type possesses different tensile strengths,yield behaviors,and strain hardening behaviors.This can be attributed to different strain distribution caused by the structural morphology;band-structure steels exhibit a yield plateau primarily attributed to the relatively weak constraint effect of pearlite on ferrite;net-structure steels display 3 strain hardening stages due to the staged plastic deformation;fiber-structure steels achieve superior strength through their uniform stress distribution.Furthermore,the initial strain hardening rate,transition strain,and uniform elongation were influenced by the features of the constituent phases.Based on these findings,methods for estimating the yield strength and tensile strength of the steels with two phases were discussed and experimentally validated.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
With the increasing demand for high-performance metallic materials,the improvement of fatigue strength(FS)has become a crucial issue.This study focuses on the AISI 52100 steel,a material with leading fatigue performan...With the increasing demand for high-performance metallic materials,the improvement of fatigue strength(FS)has become a crucial issue.This study focuses on the AISI 52100 steel,a material with leading fatigue performance and low-cost raw material,aiming to further improve its FS.It is found that the fatigue damage mechanism of 52100 steels with different tensile strengths has undergone significant changes,and the inclusions,mainly nitride and oxide,are key factors limiting the further improvement of FS.Therefore,the size reduction and modification of inclusions were attempted through the rare earth addition and strict control of harmful elements.Combining targeted microstructure adjustment,the FS of the 52100 steel has been further enhanced to~1.6 GPa,exceeding that of other metallic materials(performed in uniaxial tension with a stress ratio of R=0.1),and thus establishing it as a standout for its exceptional performance-to-cost ratio.By clarifying the influences of different types of inclusions on fatigue performance and establishing the correlation between micro-hardness(or strength)and FS,an optimization strategy for FS improvement of the 52100 steel was proposed.The FS has been improved by approximately 187 MPa at most by implementing this strategy.These achievements provide feasible technical approaches and theoretical foundations for the anti-fatigue design of metallic materials.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
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
Retained austenite plays a significant role in third-generation advanced high-strength steels (AHSS 3. Gen.), renowned for their excellent combination of strength and ductility. Silicon (Si) is a key element in stabil...Retained austenite plays a significant role in third-generation advanced high-strength steels (AHSS 3. Gen.), renowned for their excellent combination of strength and ductility. Silicon (Si) is a key element in stabilizing retained austenite. However, it introduces challenges in galvannealing and welding processes in Zn-coated steels, such as inhibited Fe-Zn alloying and increased susceptibility to liquid metal embrittlement (LME). This study investigated the mechanism of Si enrichment at the Zn/steel interface and its role in suppressing Fe-Zn interdiffusion during annealing. Using advanced techniques such as high-resolution transmission electron microscopy and atomic probe tomography, and Thermo-Calc DICTRA simulations, we analyzed the diffusion behavior and microstructural evolution in Zn-coated steels with varying Si contents. Si, driven by its low solubility in liquid Zn and Fe-Zn intermetallic phases, accumulates at the interface, forming a Si-enriched region that significantly suppresses Zn diffusion while permitting limited Fe diffusion. Numerical simulations revealed that the Si-enriched layer forms via the drag effect of the Fe-Zn reaction line, progressively concentrating Si at the interface as Zn diffuses. As annealing progresses, the morphology of the Si-enriched region evolves from layered, cloud-like structures to droplets and elongated dendritic forms, driven by Zn penetration and Fe consumption. These findings provide novel insights into the role of Si enrichment in mitigating LME and optimizing the Zn-coated AHSS 3. Gen., paving the way for advancements in automotive material design.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
Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors inclu...Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.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
Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and...Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and dual-phase(DP)steels always focus on improving the tensile ductility for stretch formability,while ignoring their limited fracture strain.In this work,we explored a novel strategy,i.e.,developing a high fracture strain ferrite-martensite dual-phase steel(HFS-DP)maintaining good strength–ductility balance by suppressing intense strain localization during deformation and enhancing martensite deformability via microstructure design including grain refinement,nano-precipitate hardening in soft ferrite phase,low-carbon and high fraction martensite.HFS-DP demonstrates a remarkable 26%and 47%improvement in tensile ductility and fracture strain,respectively,compared to commercial DP1180 steel with similar ultimate tensile strength.Furthermore,HFS-DP also exhibits a substantial 39%improvement in fracture strain compared to retained austenite-involved commercial QP1180 steel.The detailed processes of strain partitioning,strain localization,and damage formation during deformation were revealed through in-situ scanning electron microscopy(SEM)observation combined with digital image correlation(DIC).The results indicate that the excellent coordinated deformation between ferrite and martensite,coupled with microstructure refinement,effectively suppresses intense strain localization.Moreover,the excellent martensite deformability resulting from the low carbon content also aids in retarding crack formation.This combination effectively suppresses damage initiation and development during deformation,therefore the fracture strain is significantly improved.This study not only contributes to a deeper understanding of the strain localization and damage process during tensile deformation of DP steels,but also provides a new perspective on designing ultrahigh strength steels with high ductility and fracture strain.展开更多
Hydrogen embrittlement(HE)is one of the most dangerous yet most elusive embrittlement problems in metallic materials.Advanced high-strength steels(AHSS)are particularly prone to HE,as evidenced by the serious degradat...Hydrogen embrittlement(HE)is one of the most dangerous yet most elusive embrittlement problems in metallic materials.Advanced high-strength steels(AHSS)are particularly prone to HE,as evidenced by the serious degradation of their load-bearing capacity with the presence of typically only a few parts-per-million H.This strongly impedes their further development and application and could set an abrupt halt for the weight reduction strategies pursued globally in the automotive industry.It is thus important to understand the HE mechanisms in this material class,in order to develop effective H-resistant strategies.Here,we review the related research in this field,with the purpose to highlight the recent progress,and more importantly,the current challenges toward understanding the fundamental HE mechanisms in modern AHSS.The review starts with a brief introduction of current HE models,followed by an overview of the state-of-the-art micromechanical testing techniques dedicated for HE study.Finally,the reported HE phenomena in different types of AHSS are critically reviewed.Focuses are particularly placed on two representative multiphase steels,i.e.,ferrite–martensite dual-phase steels and ferrite–austenite medium-Mn steels,with the aim to highlight the multiple dimensions of complexity of HE mechanisms in complex AHSS.Based on this,open scientific questions and the critical challenges in this field are discussed to guide future research efforts.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
基金financially supported by the National Natural Science Foundation of China(Nos.52204345 and 52474361)the Scientific Research Innovation Projects of Graduate Student of Jiangsu province,China(No.KYCX24_4184)。
文摘The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.
基金financially supported by the National Key R&D program(no.2022YFB3707501)GDAS’Project of Sci-ence and Technology(no.2021GDASYL-20210102002)+1 种基金Guangdong Provincial Project(nos.2022A0505050053,2021B1515120071,and 2020B1515130007)National Natural Science Foundation of China(no.52130102).
文摘The low damage resistance and fracture toughness hinder the widespread application of ultrahighstrength dual phase(DP)steels.In this work,we propose a novel strategy to improve the fracture toughness of ultrahigh-strength DP steels by an order of magnitude without sacrificing the tensile strength.Six ultrahigh-strength DP steels with varying microstructure but comparable tensile strength(>1400 MPa)were prepared via tailoring the heat treatment process after cold rolling.Additionally,finite element(FE)method incorporated with Gurson-Tvergaad-Needleman(GTN)model and cohesive zone model(CZM)is established to simulate the fracture behavior of DP steel.Twelve model DP steels with different ferrite sizes and F/M strength differences are constructed.The combined experiment and simulation results demonstrate that(i)ferrite/martensite(F/M)interface decohesion prevails in all steels,(ii)the ferrite morphology has a strong influence on the fracture toughness of ultrahigh-strength DP steels,(iii)the effects of matrix type,ferrite size,and F/M hardness difference on the fracture toughness are relatively weak,(iv)the exceptional high fracture toughness of plate-like DP steel can be attributed to the crack deflection,crack divider and crack arrester mechanisms induced by F/M interface decohesion.
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funded by the National Key Research and Development Program of China(No.2022YFB3708200)。
文摘A series of high-strength wind power steels with various microstructural morphologies was produced by hot-rolled and thermo-mechanical controlled processes.The microstructure,microhardness,and tensile behavior observed using in-situ techniques in various types of steels were investigated.The experimental results demonstrated that the 3 microstructural morphologies(band-,net-,and fiber-structures)can be clarified and categorized;each type possesses different tensile strengths,yield behaviors,and strain hardening behaviors.This can be attributed to different strain distribution caused by the structural morphology;band-structure steels exhibit a yield plateau primarily attributed to the relatively weak constraint effect of pearlite on ferrite;net-structure steels display 3 strain hardening stages due to the staged plastic deformation;fiber-structure steels achieve superior strength through their uniform stress distribution.Furthermore,the initial strain hardening rate,transition strain,and uniform elongation were influenced by the features of the constituent phases.Based on these findings,methods for estimating the yield strength and tensile strength of the steels with two phases were discussed and experimentally validated.
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financially supported by the National Key Research and Development Program of China(No.2022YFB3705200)the National Natural Science Foundation of China(NSFC)(Nos.52321001,52130002 and 52371123)the IMR Innovation Fund(No.2024-PY07).
文摘With the increasing demand for high-performance metallic materials,the improvement of fatigue strength(FS)has become a crucial issue.This study focuses on the AISI 52100 steel,a material with leading fatigue performance and low-cost raw material,aiming to further improve its FS.It is found that the fatigue damage mechanism of 52100 steels with different tensile strengths has undergone significant changes,and the inclusions,mainly nitride and oxide,are key factors limiting the further improvement of FS.Therefore,the size reduction and modification of inclusions were attempted through the rare earth addition and strict control of harmful elements.Combining targeted microstructure adjustment,the FS of the 52100 steel has been further enhanced to~1.6 GPa,exceeding that of other metallic materials(performed in uniaxial tension with a stress ratio of R=0.1),and thus establishing it as a standout for its exceptional performance-to-cost ratio.By clarifying the influences of different types of inclusions on fatigue performance and establishing the correlation between micro-hardness(or strength)and FS,an optimization strategy for FS improvement of the 52100 steel was proposed.The FS has been improved by approximately 187 MPa at most by implementing this strategy.These achievements provide feasible technical approaches and theoretical foundations for the anti-fatigue design of metallic materials.
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 Fundamental Research Program of the Korea Institute of Materials Science(No.PNK9820).
文摘Retained austenite plays a significant role in third-generation advanced high-strength steels (AHSS 3. Gen.), renowned for their excellent combination of strength and ductility. Silicon (Si) is a key element in stabilizing retained austenite. However, it introduces challenges in galvannealing and welding processes in Zn-coated steels, such as inhibited Fe-Zn alloying and increased susceptibility to liquid metal embrittlement (LME). This study investigated the mechanism of Si enrichment at the Zn/steel interface and its role in suppressing Fe-Zn interdiffusion during annealing. Using advanced techniques such as high-resolution transmission electron microscopy and atomic probe tomography, and Thermo-Calc DICTRA simulations, we analyzed the diffusion behavior and microstructural evolution in Zn-coated steels with varying Si contents. Si, driven by its low solubility in liquid Zn and Fe-Zn intermetallic phases, accumulates at the interface, forming a Si-enriched region that significantly suppresses Zn diffusion while permitting limited Fe diffusion. Numerical simulations revealed that the Si-enriched layer forms via the drag effect of the Fe-Zn reaction line, progressively concentrating Si at the interface as Zn diffuses. As annealing progresses, the morphology of the Si-enriched region evolves from layered, cloud-like structures to droplets and elongated dendritic forms, driven by Zn penetration and Fe consumption. These findings provide novel insights into the role of Si enrichment in mitigating LME and optimizing the Zn-coated AHSS 3. Gen., paving the way for advancements in automotive material design.
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supported by the Natural Science Foundation Project of Liaoning province(Nos.2023-MS-017 and 2022-MS-005)the National Science and Technology Major Project(No.J2019-VI-0019-0134)+2 种基金the National Natural Science Foundation of China(Nos.52201028 and 52188101)the Project funded by China Postdoctoral Science Foundation(No.2021M700153)the Special Projects of the Central Government in Guidance of Local Science and Technology Development(No.2024010859-JH6/1006).
文摘Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.
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 National Natural Science Foundation of China(No.52101128)the Jiangsu Provincial Key Research and Development Program(No.BE023059)+1 种基金the Post-doctoral Science Foundation of China(No.2022M710021)the Northeastern University Postdoctoral Research Fund of China(No.20220202).
文摘Fracture strain becomes critical for the local formability and crash performance of carbody components when the tensile strength exceeds 1000 MPa.Regrettably,high-strength quenching and partitioning(Q&P)steels and dual-phase(DP)steels always focus on improving the tensile ductility for stretch formability,while ignoring their limited fracture strain.In this work,we explored a novel strategy,i.e.,developing a high fracture strain ferrite-martensite dual-phase steel(HFS-DP)maintaining good strength–ductility balance by suppressing intense strain localization during deformation and enhancing martensite deformability via microstructure design including grain refinement,nano-precipitate hardening in soft ferrite phase,low-carbon and high fraction martensite.HFS-DP demonstrates a remarkable 26%and 47%improvement in tensile ductility and fracture strain,respectively,compared to commercial DP1180 steel with similar ultimate tensile strength.Furthermore,HFS-DP also exhibits a substantial 39%improvement in fracture strain compared to retained austenite-involved commercial QP1180 steel.The detailed processes of strain partitioning,strain localization,and damage formation during deformation were revealed through in-situ scanning electron microscopy(SEM)observation combined with digital image correlation(DIC).The results indicate that the excellent coordinated deformation between ferrite and martensite,coupled with microstructure refinement,effectively suppresses intense strain localization.Moreover,the excellent martensite deformability resulting from the low carbon content also aids in retarding crack formation.This combination effectively suppresses damage initiation and development during deformation,therefore the fracture strain is significantly improved.This study not only contributes to a deeper understanding of the strain localization and damage process during tensile deformation of DP steels,but also provides a new perspective on designing ultrahigh strength steels with high ductility and fracture strain.
文摘Hydrogen embrittlement(HE)is one of the most dangerous yet most elusive embrittlement problems in metallic materials.Advanced high-strength steels(AHSS)are particularly prone to HE,as evidenced by the serious degradation of their load-bearing capacity with the presence of typically only a few parts-per-million H.This strongly impedes their further development and application and could set an abrupt halt for the weight reduction strategies pursued globally in the automotive industry.It is thus important to understand the HE mechanisms in this material class,in order to develop effective H-resistant strategies.Here,we review the related research in this field,with the purpose to highlight the recent progress,and more importantly,the current challenges toward understanding the fundamental HE mechanisms in modern AHSS.The review starts with a brief introduction of current HE models,followed by an overview of the state-of-the-art micromechanical testing techniques dedicated for HE study.Finally,the reported HE phenomena in different types of AHSS are critically reviewed.Focuses are particularly placed on two representative multiphase steels,i.e.,ferrite–martensite dual-phase steels and ferrite–austenite medium-Mn steels,with the aim to highlight the multiple dimensions of complexity of HE mechanisms in complex AHSS.Based on this,open scientific questions and the critical challenges in this field are discussed to guide future research efforts.
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.%.
