Effect of Cooling Practice on the Mechanical Properties of Medium-Manganese Aluminum-Alloyed Steels after Intercritical Annealing Quench and Partition Treatment

Abstract

This study reports the effect of different cooling practices after hot rolling on the microstructure and mechanical properties of intercritically annealed quench and partitioned low-carbon medium-manganese aluminum-alloyed steel. The outcomes show that the tensile strength and uniform elongation of medium-manganese steels can be improved by manipulating the cooling cycle after hot rolling. The starting microstructure, obtained after hot rolling and cooling, influences the fraction of austenite formed at the end of intercritical annealing, thereby impacting the fraction of martensite produced at the interrupted quenching step. The results illustrate that during intercritical annealing austenite tends to nucleate at a higher temperature from a ferritic microstructure compared to a microstructure consisting of mainly bainite or a mixture of ferrite, martensite, cementite, and retained austenite. Partition temperature of 400 °C facilitates the partition of carbon from martensite to austenite while partition temperature of 450 °C supports the formation of high carbon secondary martensite.