Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas (MIG) welded with NiCrMo-3 and 307Si filler wires. The effect of filler wires on the microstructure and mechanical properties of joint was investigated, and the carbide precipitates were contrastively discussed. The results revealed that the microstructure of weld metal, heat-affected zone and base metal are austenite. Obvious grain coarsening occurred in the heat-affected zone (HAZ), and the maximum grain size grew up to 160 mu m. In HAZ, C and Cr segregated at grain boundaries, the carbides was identified as Cr7C3. The dispersive (Nb, Mo)C phase was also found in weld metal with NiCrMo-3 filler wire. All the welded joints failed in HAZ during tensile tests. The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa, which is much higher than that with 307Si filler wire. In comparison to base metal, higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints, which was attributed to the precipitation of Cr7C3 phase and grain coarsening. The impact toughness around the fusion line is the worst for these two welded joints. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The effects of NiCrMo-3 and 307Si filler wires on the microstructure and mechanical properties of medium Mn steel joints were investigated. The joints with NiCrMo-3 filler wire exhibited higher tensile strength, increased microhardness, and reduced impact toughness compared to those with 307Si filler wire. The worst impact toughness was observed around the fusion line in both welded joints.