A novel Si-Al alloyed press hardening steel(PHS)with the ferrite(α)-austenite(γ)-martensite(α')triplex microstructure was developed to have marginal oxidization after the hot forming in air,and the resultant ul...A novel Si-Al alloyed press hardening steel(PHS)with the ferrite(α)-austenite(γ)-martensite(α')triplex microstructure was developed to have marginal oxidization after the hot forming in air,and the resultant ultimate tensile strength(UTS)of 1620 MPa and total elongation(TE)of 14%were achieved simultaneously at reduced density.Both performances are superior to the existing PHSs.Particularly,the baking at 170°C leads to remarkable increases in both strength and ductility together with the transition of tensile fracture from the brittle interfacial cracking to the ductile one.This is because austenite and ferrite were hardened due to the segregation of C atoms into geometry necessary dislocations(GNDs)but martensite softened due to the loss of supersaturated C atoms during the baking.Atomic probe tomography examination reveals that some C atoms segregated to theα/α'interfaces during the baking for increased cohesive energy of the phase interface,thus hindering the interfacial cracking.In addition,the employed Al/Si alloying affords stronger oxidization resistance than both Al/Cr and Si/Cr because they are more rapidly oxidized than Cr to form the dense Al_(2) O_(3)/SiO_(2) layers for earlier protection.展开更多
基金financially supported by the National Natu-ral Science Foundation of China(Nos.52233018 and 51831002)。
文摘A novel Si-Al alloyed press hardening steel(PHS)with the ferrite(α)-austenite(γ)-martensite(α')triplex microstructure was developed to have marginal oxidization after the hot forming in air,and the resultant ultimate tensile strength(UTS)of 1620 MPa and total elongation(TE)of 14%were achieved simultaneously at reduced density.Both performances are superior to the existing PHSs.Particularly,the baking at 170°C leads to remarkable increases in both strength and ductility together with the transition of tensile fracture from the brittle interfacial cracking to the ductile one.This is because austenite and ferrite were hardened due to the segregation of C atoms into geometry necessary dislocations(GNDs)but martensite softened due to the loss of supersaturated C atoms during the baking.Atomic probe tomography examination reveals that some C atoms segregated to theα/α'interfaces during the baking for increased cohesive energy of the phase interface,thus hindering the interfacial cracking.In addition,the employed Al/Si alloying affords stronger oxidization resistance than both Al/Cr and Si/Cr because they are more rapidly oxidized than Cr to form the dense Al_(2) O_(3)/SiO_(2) layers for earlier protection.
基金the National Natural Science Foundation of China (Grant Nos.21474035and 51773072)the Recruitment Program of Global Youth Experts,the Huazhong University of Science and Technology (HUST)Innovation Research Fund (Nos. 2016JCTD 111and 2017KFKJXX012)+1 种基金the Science and Technology Program of Hubei Province (No.2017AHB040) China Postdoctoral Science Foundation funded project (No.2016M602289).
