On the Significant Impact of Deformation Coupled with Cooling Rate during Thermo‐Mechanical Controlled Processing (TMCP) on Microstructure‐Property Relationship in 25Mn2Si2Cr High Strength Steel

Abstract

To elucidate the effect of deformation and cooling rate on microstructure‐property relationship in 25Mn2Si2Cr high strength steel during TMCP process, the dynamic continuous cooling transformation (CCT) curves are first determined by thermal simulation experiments with different degree of deformation (engineering strain: 0.35, 0.50, 0.65) and cooling rate. At the same time, direct cooling after rolling experiments are carried out with different degree of deformation and cooling rate. The results indicate that dynamic CCT curves are changed by increasing the degree of deformation. The high temperature phase transformation zone moves to left. The start temperature of martensitic transformation (Ms) is decreased. The microstructure is composed of granular bainite (GB), lath bainite (LB), and martensite/austenite (M/A) islands after air cooling (cooling rate: about 1 °C s−1). When the cooling method was wind cooling (cooling rate: about 2.5 °C s−1), microstructure was a combination of lath bainite and martensite. The microstructure on water cooling (cooling rate: about 30 °C s−1) was primarily martensite. Accelerating the cooling rate, the strength was increased, but toughness was decreased. While increasing the degree of deformation increased strength and toughness simultaneously.