5th International High Manganese Steel Conference - HMNS 2022

Hot rolled medium Mn steel was arc welded by employing a E-71T-GS flux cored filler in a butt joint with 3 mm in thickness. The initial microstructure of the sheet was composed of martensite and very little amount of austenite, the ultimate tensile strength in this condition was close to 1600 MPa with a negligible elongation. A post-heat treatment of intercritical annealing was proposed in order to promote the austenite reversion in the heat affected zone (HAZ) and to increase the amount and stability of this phase. Thermodynamic simulations and previous experimental results were used to determine the temperature and time for the IA treatment. Before IA the microstructure in the fusion zone (FZ) was completely lath α´-martensite, the heat affected zone (HAZ) comprises austenite and α´-martensite, and the base metal (BM) comprises only α´-martensite; after IA the major change was observed in the HAZ on which the austenite amount was increased. After welding microhardness values were the highest at the fusion zone and then a slightly decrement of 50 HV was detected in the HAZ while a significant decrement of 125 HV was observed in the base metal. After IA these differences in the microhardness were attenuated in the three areas. Finally, the steel experimented a reduction of around 50% of the tensile strength after welding without IA in comparison to the hot rolled steel.