Microstructure and mechanical properties of a gas-tungsten-arc-welded Fe-24Mn-3.5Cr-0.4C high manganese steel pipe using a Fe-22Mn-2.34Ni-0.38C welding wire

Abstract

In this study, Fe-24.34Mn-3.53Cr-0.42C high manganese steel sheets were joined using a gas‑tungsten arc welding (GTAW) and a plasma arc welding (PAW) using a newly-developed Fe-22.2Mn-2.34Cr-1.95Ni welding wire. Microstructure analysis revealed that Mn-depleted zone appeared in the weld zone due to Mn segregation during solidification. With plastic deformation, a small amount of ε-martensite was found in the Mn-depleted zone i.e., dendritic region, of the weld zone. Mechanical properties of the weld zone were found to be lower than in the base metal. On the other hand, due to recrystallization and grain growth induced by heat treatment at 1050 °C, the mechanical property differences between the base metal and the weld zone were reduced. Strain rate sensitivity test showed negative strain rate sensitivity in the base metal and heat-treated weld zone possibly due to the reduced work hardening caused by the reduction of twinning nucleation. On the contrary, the as-welded zone exhibited positive strain rate sensitivity due to the reduction in twinning stress caused by coarse grains. • The SFE of Mn-depleted zones decreased due to manganese segregation in weld zones, and low manganese content in welding wires. • Therefore, ε-martensite was formed in Mn-depleted zones due to transformation-induced plasticity effects during plastic deformation. • In weld zones, mechanical properties were improved, and their anisotropy also decreased largerly due to recrystallization effects through heat treatment. • Except for as-welded zone, twin formation decreased with increasing strain rate, thus showing negative strain rate sensitivity.