Influence of initial microstructures on intercritical annealing behaviour in a medium Mn steel

The present work reports the effect of different initial microstructures on reverse transformation kinetics and morphologies of austenite formed during intercritical annealing in Fe-0.14C-7Mn-1Si (wt-%) medium Mn steel. Three different initial microstructures were produced by cold-rolling and cold-rolling followed by austenitisation at 820°C and 900°C. The specimen austenitised at higher temperature shows lath-type austenite after intercritical annealing. The difference in austenitisation temperature leads to different Mn distribution in martensitic initial microstructures, thereby leading to a difference in morphology of austenite. The inhomogeneous Mn profiles in initial microstructures also affect reverse transformation kinetics of austenite upon intercritical annealing. The presence of Mn-enriched regions accelerates austenite growth at an early stage of intercritical annealing but retards the transformation kinetics afterwards