Analysis of microstructural evolution and mechanical properties in the simulated heat-affected zone of Fe-23Mn-0.45C-1.5Al high-Mn austenitic steel

Abstract

Welding thermal simulation technology was used to process Fe-23Mn-0.45C-1.5Al high-Mn austenitic steel to reproduce the heat-affected zone (HAZ) and investigate the effect of peak temperature on microstructural evolution and cryogenic toughness. Subsequently, the simulated HAZ samples experienced isothermal aging at 500 °C for different time to clarify the embrittlement mechanism. The results revealed that phase transformation was absent in simulated HAZ sample. However, with the increase of peak temperature (Tp) in thermal cycles from 1050 °C to 1320 °C, the grain size, carbide precipitates at grain boundaries, grain boundary segregation of carbon and the proportion of low angle grain boundaries increase gradually, while the proportion of high angle grain boundaries decrease. When Tp was above 1200 °C, granular M7C3-type and rod-shaped M23C6-type carbides precipitated at grain boundaries. Impact absorbed energy of simulated sample at room and cryogenic temperatures decreased with the increase of Tp. The impact energy of experiment steel is 228 J at room temperature. When the Tp increased to 1050 °C, 1200 °C and 1320 °C, the impact absorbed energy of simulated sample decreased to 208 J, 174 J and 142 J, respectively. The variation trends of impact absorbed energy for aged samples manifested that the precipitation of M23C6-type or M7C3-type carbides at grain boundaries was the main factor causing the embrittlement of HAZ, and then the segregation of carbon at grain boundary and high proportion of low angle grain boundaries were the secondary factor causing the deterioration of impact toughness.