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

作者：Zhang, Jinshuai; Li, Guangqiang^*; Wang, Honghong^*; Wan, Xiangliang; Hu, Mingfeng; Meng, Qingrun

来源：Welding in the World, 2022, 66(11): 2281-2295.

DOI：10.1007/s40194-022-01365-7

• High-Mn austenitic weld metal
• Inclusion
• Cryogenic impact toughness
• Fracture
• Dimple

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 celcius 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 TiO2, Mn2SiO4, and MnAl2O4, respectively. The finer and dispersed MnAl2O4 in WM-3 weld metal has a lower lattice mismatch with gamma-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.