Influence of band microstructure on carbide precipitation behavior and tough-ness of 1 GPa-grade ultra-heavy gauge low-alloy steel

• Published in: 矿物冶金与材料学报 Vol. 30; no. 7; pp. 1329 - 1337
• Main Authors: Peng Han, Zhipeng Liu, Zhenjia Xie, Hua Wang, Yaohui Jin, Xuelin Wang, Chengjia Shang
• Format: Journal Article
• Language: English
• Published: Collaborative Innovation Center of Steel Technology,University of Science and Technology Beijing,Beijing 100083,China 2023; Yangjiang Branch,Guangdong Laboratory for Materials Science and Technology(Yangjiang Advanced Alloys Laboratory),Yangjiang 529500,China; State Key Laboratory of Metal Material for Marine Equipment and Application,Anshan 114000,China%Collaborative Innovation Center of Steel Technology,University of Science and Technology Beijing,Beijing 100083,China%State Key Laboratory of Metal Material for Marine Equipment and Application,Anshan 114000,China%Collaborative Innovation Center of Steel Technology,University of Science and Technology Beijing,Beijing 100083,China
• Subjects: carbides; heavy gauge steel; centerline segregation; band microstructure; toughness
• ISSN: 1674-4799; 1869-103X

This study investigated the influence of band microstructure induced by centerline segregation on carbide precipitation behavior and toughness in an 80 mm-thick 1 GPa low-carbon low-alloy steel plate. The quarter-thickness (1/4t) and half-thickness (1/2t) regions of the plate exhibited similar ductility and toughness after quenching. After tempering, the 1/4t region exhibited ～50％ and ～25％ enhancements in both the total elongation and low-temperature toughness at ?40℃, respectively, without a decrease in yield strength, whereas the toughness of the 1/2t region decreased by ～46％. After quenching, both the 1/4t and 1/2t regions exhibited lower bainite and lath martensite concentrations, but only the 1/2t region exhibited microstructure bands. Moreover, the tempered 1/4t region featured uniformly dispersed short rod-like M23C6 carbides, and spherical MC precipitates with diameters of ～20–100 nm and <20 nm, respectively. The uniformly dispersed nanosized M23C6 carbides and MC precipitates contributed to the balance of high strength and high toughness. The band microstructure of the tempered 1/2t region fea-tured a high density of large needle-like M3C carbides. The length and width of the large M3C carbides were ～200–500 nm and ～20–50 nm, re-spectively. Fractography analysis revealed that the high density of large carbides led to delamination cleavage fracture, which significantly de-teriorated toughness.