The microstructure and mechanical properties of novel cryogenic twinning-induced plasticity steel welded joint

Thick Fe-23Mn-1.5Al-0.45C high-Mn steel plates were multi-pass metal inert gas (MIG) welded with 307Si stainless steel wire. The microstructure, grain orientation and grain boundary evolution of the joint were investigated. The toughness impact at ambient and cryogenic temperatures, the microhardness and tensile strength were also measured. The weld metal (WM) is mainly composed of columnar dendrites, and the growth of grains in WM has obvious preferred orientation and significant stress concentration exists in the heat-affected zone (HAZ) and WM. In comparison to base material (BM), lower cryogenic impact toughness was obtained in WM, which was attributed to the precipitation of rod-shaped M7C3 carbide and the high proportion of low angle grain boundaries in WM. The microhardness is higher in HAZ than in BM, and the average microhardness of each pass weld is very different. The joint strength and efficiency are 669 MPa and 91.5%, respectively. With the decrease of impact test temperature (25 degrees C, 0 degrees C, -40 degrees C, -196 degrees C), the impact toughness of BM and WM both decreased and the fracture mode of WM diverted from ductile to intergranular brittle.

Automated summary

In this study, thick Fe-23Mn-1.5Al-0.45C high-Mn steel plates were MIG welded with 307Si stainless steel wire, and the microstructure, grain orientation, and grain boundary evolution of the joint were investigated. The results showed that the growth of grains in the weld metal had obvious preferred orientation, leading to significant stress concentration in the heat-affected zone and weld metal, resulting in decreased cryogenic impact toughness of the joint.