The strength-ductility trade-off in low-Mn lightweight steels is a significant challenge due to the low thermal stability of austenite and the presence ofδ-ferrite.Two types of low-Mn lightweight steels containing V ...The strength-ductility trade-off in low-Mn lightweight steels is a significant challenge due to the low thermal stability of austenite and the presence ofδ-ferrite.Two types of low-Mn lightweight steels containing V and NbVMo microalloying elements were developed by warm rolling.Among these,NbVMo steel demonstrated superior properties,achieving a tensile strength of~1.2 GPa and a product of strength and elongation exceeding 45 GPa%.In-depth mechanism analysis by atom probe tomography and quasi-in-situ electron backscatter diffraction revealed that different microalloying compositions influence the mechanical properties by strengtheningδ-ferrite,refining retained austenite and homogenizing matrix strain.In NbVMo steel,δ-ferrite strengthening is attributed to the synergistic effects of(V,Mo,Cr,Nb)C composite precipitation,fine NbC and MoC precipitates,and the solid solution strengthening of Mo.These mechanisms collectively contribute to a higher yield strength andδ-ferrite microhardness compared to V steel.Consequently,δ-ferrite and the surrounding matrix in NbVMo steel exhibit coordinated elongation during deformation,enhancing the ductility.The improved microstructural and strain uniformity in NbVMo steel mitigates stress concentration effects onδ-ferrite deformation and serves as a barrier that delays the transformation of retained austenite.In contrast,the retained austenite in V steel exhibits a blocky morphology with larger grain sizes,resulting in lower stability.Combined with localized stress concentrations due to non-uniform strain distribution,this leads to premature transformation of retained austenite to alleviate stress,ultimately impairing elongation and the continuity of strain hardening.Furthermore,the precipitation mechanisms of(V,Mo,Cr,Nb)C composite precipitates are elucidated.展开更多
对DH36钢母材及焊接热影响区开展单电解池充氢试验和慢应变速率拉伸试验,结合扫描电镜等表征手段探究了充氢电流密度对DH36钢氢脆敏感性的影响。结果表明,充氢后母材及焊接热影响区的抗拉强度和塑性均降低。在50 m A/cm^(2)的充氢电流...对DH36钢母材及焊接热影响区开展单电解池充氢试验和慢应变速率拉伸试验,结合扫描电镜等表征手段探究了充氢电流密度对DH36钢氢脆敏感性的影响。结果表明,充氢后母材及焊接热影响区的抗拉强度和塑性均降低。在50 m A/cm^(2)的充氢电流密度时,母材和焊接热影响区的氢脆敏感性指数最大;继续增大充氢电流密度,母材的氢脆敏感性略下降,而焊接热影响区的则先下降后升高。充氢后,母材和焊接热影响区的拉伸断裂方式均由韧性断裂变为脆性断裂且颈缩现象逐渐消失,焊接热影响区的拉伸断口在充氢电流密度为100 m A/cm^(2)时出现了部分韧性断裂的特征。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
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.FRF-BD-25-001)Development and Application of Ultra-High Strength Hot Stamping Steel Strip for Automobiles(Grant No.20232BCJ22030)Manufacturing and Application Innovation and Integration of High-Safety Automotive Steel(Grant No.24431002D).
文摘The strength-ductility trade-off in low-Mn lightweight steels is a significant challenge due to the low thermal stability of austenite and the presence ofδ-ferrite.Two types of low-Mn lightweight steels containing V and NbVMo microalloying elements were developed by warm rolling.Among these,NbVMo steel demonstrated superior properties,achieving a tensile strength of~1.2 GPa and a product of strength and elongation exceeding 45 GPa%.In-depth mechanism analysis by atom probe tomography and quasi-in-situ electron backscatter diffraction revealed that different microalloying compositions influence the mechanical properties by strengtheningδ-ferrite,refining retained austenite and homogenizing matrix strain.In NbVMo steel,δ-ferrite strengthening is attributed to the synergistic effects of(V,Mo,Cr,Nb)C composite precipitation,fine NbC and MoC precipitates,and the solid solution strengthening of Mo.These mechanisms collectively contribute to a higher yield strength andδ-ferrite microhardness compared to V steel.Consequently,δ-ferrite and the surrounding matrix in NbVMo steel exhibit coordinated elongation during deformation,enhancing the ductility.The improved microstructural and strain uniformity in NbVMo steel mitigates stress concentration effects onδ-ferrite deformation and serves as a barrier that delays the transformation of retained austenite.In contrast,the retained austenite in V steel exhibits a blocky morphology with larger grain sizes,resulting in lower stability.Combined with localized stress concentrations due to non-uniform strain distribution,this leads to premature transformation of retained austenite to alleviate stress,ultimately impairing elongation and the continuity of strain hardening.Furthermore,the precipitation mechanisms of(V,Mo,Cr,Nb)C composite precipitates are elucidated.
文摘对DH36钢母材及焊接热影响区开展单电解池充氢试验和慢应变速率拉伸试验,结合扫描电镜等表征手段探究了充氢电流密度对DH36钢氢脆敏感性的影响。结果表明,充氢后母材及焊接热影响区的抗拉强度和塑性均降低。在50 m A/cm^(2)的充氢电流密度时,母材和焊接热影响区的氢脆敏感性指数最大;继续增大充氢电流密度,母材的氢脆敏感性略下降,而焊接热影响区的则先下降后升高。充氢后,母材和焊接热影响区的拉伸断裂方式均由韧性断裂变为脆性断裂且颈缩现象逐渐消失,焊接热影响区的拉伸断口在充氢电流密度为100 m A/cm^(2)时出现了部分韧性断裂的特征。
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.
