5th International High Manganese Steel Conference - HMNS 2022

The development of new-generation AHSS steels requires a careful optimization of their processing parameters. In the case of intercritically annealed medium-Mn steels, parameters as the initial microstructure, annealing time and temperature and cooling and heating rates are paramount in controlling the final response of the microstructure.
The present research concerns with the effect that increasing intercritical annealing time (1 to 300 min) has on the morphology, size distribution, and stability of the final microstructure constituents (austenite and ferrite). The steel with composition 0.16C, 4.7Mn, 1.6Al, 0.2Si, 0.2Mo in hot rolled conditions with initial microstructure of martensite was used. The temperature for the intercritical treatment of 680°C, has been selected on the basis of previous studies seeking for the highest fraction of stable retained austenite at room temperature after soaking for 60 min.
This work aims to clarify how intercritical annealing time affects retained austenite fraction, grain size and distribution of Mn, which are paramount in defining austenite stability (thermal and mechanical). Results thus obtained, indicated a significant increase of retained austenite fraction, lath thickness and grains merging with increasing annealing time. The retained austenite fraction increase from 8% to 35% when intercritical time increase from 1 to 300 min, also accompanied by a considerable decrease in the fraction of austenite grains with an area below 1 μm2 , from almost 100% to less than 20% respectively.