Effect of Al on the Microstructure and Mechanical Properties of Hot-Rolled Medium-Mn Steel

The present investigation was made to study the effect of Al on the microstructure and mechanical properties of hot-rolled medium-Mn TRIP steel ( abbreviated as Al-TRIP). As a contrast, a Si-added medium-Mn TRIP steel ( abbreviated as Si-TRIP) was also studied. Addition Al in medium-Mn steel can raise A(c3) temperature, which will restrain austenite transformation and expand the two-phase region, promoting Mn and C elements enriched in austenite. In-depth microstructure and mechanical properties analysis were carried out for the hot-rolled Al-TRIP and Si-TRIP steels in this study. The microstructure was characterized by scanning electron microscope ( SEM) and electron probe microanalyzer ( EPMA). Volume fraction of retained austenite was measured by D/max2400 X-ray diffractometer ( XRD). A dual-phase microstructure consisting of ultra-fine grained intercritical ferrite ( IF) and lath-like retained austenite ( RA) with high mechanical stability was obtained after annealing at 630 degrees C for 2h for Al-TRIP steel. As prolonging the intercritical annealing time, the stability of RA decreased primarily due to the increase of grain size. The tensile test results indicated that the Al-TRIP steel possessed a better combination of tensile strength and elongation compared to Si-TRIP steel. Excellent mechanical properties with yield strength of 790MPa, tensile strength of 1050MPa, total elongation of 35% and UTSxTEL of 39GPa.% was obtained for the Al-TRIP steel.