The influence of cooling methods on the austenite stability and plastic instability behavior in 3Mn steel.

The present study on 3Mn steel demonstrates that the newly proposed "intercritical annealing-tempering (IAT)" process led to different performances of austenite stability and plastic instability by adopting different cooling methods (water quenching and air cooling) in the intercritical annealing process (IA). Air cooling promoted the partitioning of C and Mn to austenite and improved the stability of austenite, accompanied by the increase of M 7 C 3 precipitation during tempering. As two competing mechanisms affecting the elements partitioning during tempering, carbon partitioning and M 7 C 3 precipitation enhanced and weaken austenite stability, respectively, and more precipitation of M 7 C 3 in IA-AT (tempering after air cooling) resulted in more austenite decomposition than that in IA-WT (tempering after water quenching). In addition, compared to the appearance of the yield plateau and stress serration in IA-WT, the suppression of plastic instability behavior in IA-AT was attributed to the rapid proliferation of geometrically necessary dislocations (GNDs) caused by the stronger TRIP effect and a large amount of M 7 C 3 precipitation. The study of microstructure evolution and plastic instability behavior induced by different annealing cooling methods would help in further optimizing the heat treatment process to achieve better mechanical properties for medium Mn steel. • Air cooling promoted the partitioning of C and Mn into austenite in IA and retained more austenite than water quenching. • During tempering, the stability of austenite was increased for the partitioning of C and reduced for more M 7 C 3 precipitation. • Rapid TRIP effect and more M 7 C 3 particles promoted the proliferation of GNDs and suppressed the plastic instability behavior. [ABSTRACT FROM AUTHOR]