Dilatometric study on decomposition of undeformed and plastically deformed supercooled austenite in medium-Mn steels alloyed with Mo and Cu additions

Abstract In the context of increasing circularity in steel recycling and the connected increasing build-up of residual elements in the steel industry, the present study investigates the influence of Mo, Cu, and hot plastic deformation on critical temperatures and phase transformation kinetics of 4 wt% Mn steel. The thermodynamic-kinetic calculations are performed using JMatPro software, and phase transformations are recorded using a high-resolution Bahr DIL805 dilatometer. The research explores equilibrium-like austenitization and continuous cooling at rates ranging from 60 to 0.05 °C/s for undeformed and 50% plastically deformed samples. All steels exhibit high hardenability as the highest critical cooling rate is below 1 °C/s. Mo and Cu alloying change A c1 , A c3 , M s, and M f temperatures, and further increase the hardenability and decrease the critical cooling rate to below 0.05 °C/s. The effect of plastic deformation on delaying the formation of bainite in all analyzed steels is observed. A newly proposed spectral deconvolution of dilatometric derivative curves, together with Klemm’s color etching, is applied for a precise determination of the phase ratio formed during continuous cooling for undeformed and plastically deformed samples. It is revealed that in some temperature range, both martensitic and bainitic transformations take place simultaneously. The research provides new insights into the phase transformation kinetics of medium-Mn steels alloyed with Mo and Cu, which are typical steel scrap elements.