The effect of non-metallic inclusions in refining microstructure and improving cryogenic toughness of novel high-Mn steel weld metals for LNG tanks

• Published in: Welding in the world 2022-11, Vol.66 (11), p.2281-2295
• Main Authors: Zhang, Jinshuai, Li, Guangqiang, Wang, Honghong, Wan, Xiangliang, Hu, Mingfeng, Meng, Qingrun
• Format: Article
• Language: English
• Subjects: Chemistry and Materials Science; Crack propagation; Cryoforming; Cryogenic properties; Crystallography; Dendritic structure; Dimpling; Ferrous alloys; Heat treating; Impact strength; Iron; Manganese steels; Materials Science; Metallic Materials; Metals; Microstructure; Nonmetallic inclusions; Nucleation; Research Paper; Solid Mechanics; Theoretical and Applied Mechanics; Titanium dioxide; Weld metal
• ISSN: 0043-2288; 1878-6669
• DOI: 10.1007/s40194-022-01365-7

In this study, the role of non-metallic inclusions on the microstructure and cryogenic toughness in the novel high-Mn steel weld metals was investigated. The cryogenic impact testing at − 196 ℃ indicated that the absorbed energy of three weld metals (WM-1, 2, 3) was 20 ± 2 J, 32 ± 2 J, and 52 ± 6 J, respectively. In the three weld metals, the non-metallic inclusions were found to be spherical and were mainly demonstrated as TiO 2 , Mn 2 SiO 4 , and MnAl 2 O 4 , respectively. The finer and dispersed MnAl 2 O 4 in WM-3 weld metal has a lower lattice mismatch with γ-Fe–Mn (austenite in the Fe–Mn alloy) than the other two weld metals. Thus, they can refine the dendritic structure and crystallographic grain more effectively through heterogeneous nucleation. The inclusions were observed to locate inside of the dimples and the large-size inclusions in the large and shallow dimples of cryogenic impact fracture. The finer, small quantity and volume fraction of inclusions in WM-3 weld metal are suggested to make crack propagation more difficult during the cryogenic impact fracture process, which form large, uniform, and deep dimples during cryogenic impacting. Therefore, the relatively good cryogenic impact toughness was obtained in WM-3 weld metal. These findings suggest that the control of inclusions can be an effective way to improve the impact toughness of the weld metal.