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

• Published in: International journal of minerals, metallurgy and materials Vol. 30; no. 7; pp. 1329 - 1337
• Main Authors: Han, Peng, Liu, Zhipeng, Xie, Zhenjia, Wang, Hua, Jin, Yaohui, Wang, Xuelin, Shang, Chengjia
• Format: Journal Article
• Language: English
• Published: Beijing University of Science and Technology Beijing 01.07.2023; Springer Nature B.V
• Subjects: Bainite; Carbides; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Corrosion and Coatings; Diameters; Dispersion; Ductility; Elongation; Glass; Heat treating; High density; Low alloy steels; Low carbon steels; Low temperature; Martensite; Materials Science; Metallic Materials; Microstructure; Natural Materials; Precipitates; Quenching; Steel plates; Surfaces and Interfaces; Thickness; Thin Films; Tribology; carbides; heavy gauge steel; centerline segregation; band microstructure; toughness
• ISSN: 1674-4799; 1869-103X
• DOI: 10.1007/s12613-023-2597-6

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°C, 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 M 23 C 6 carbides, and spherical MC precipitates with diameters of ∼20–100 nm and <20 nm, respectively. The uniformly dispersed nanosized M 23 C 6 carbides and MC precipitates contributed to the balance of high strength and high toughness. The band microstructure of the tempered 1/2t region featured a high density of large needle-like M 3 C carbides. The length and width of the large M 3 C carbides were ∼200–500 nm and ∼20–50 nm, respectively. Fractography analysis revealed that the high density of large carbides led to delamination cleavage fracture, which significantly deteriorated toughness.