Effect of Al on Microstructure and Tensile Properties of a PM Fe-22Mn-0.6C Steel

This study investigates the effects of adding 1 and 2 wt pct Al on the microstructure and tensile properties of a powder metallurgy (PM) Fe-22Mn-0.6C (wt pct) steel produced by powder compact extrusion. The addition of Al powder converted ferromanganese oxide (FMO) particles into ferromanganese-aluminum oxide (FMAO) particles via the reductive reaction, while introducing a significant number of fine Al2O3 particles ranging in sizes from 0.1 to 2 mu m. These Al2O3 particles promoted dynamic recrystallization, resulting in grain refinement (average size reduced from 63.1 to 10.5 mu m) and increased material yield strength (322 to 444 MPa) due to fine grain reinforcement. The addition of Al significantly reduced the strain hardening rate and ductility, mainly because Al inhibited the formation of twins in the mid-stage of deformation, which occurred only in grains with a Schmidt factor of less than 0.2. In addition, the ductility is further reduced due to the tendency of clustered Al2O3 particles to form larger voids during deformation.