Superior synergy of strength and ductility in carbon steel by thermomechanical processing

In this work, a simple technique consisting of asymmetric rolling and low-temperature heat treatment was proposed to fabricate medium carbon steel with a large strength-ductility balance. The heat-treated samples exhibited an inhomogeneous lamellar structure consisting of hard pearlite lamellae embedded in soft proeutectoid ferrite lamellae matrix. Many spherical cementite particles were formed in the pearlite grains after the heat treatment at 400°C. By increasing the duration of heat treatment, the number of spherical θ particles was increased. The absence of significant changes in the texture of heat-treated sheets compared to the rolled sheet demonstrated that recrystallization has not occurred during heat treatment and recovery was the main mechanism. After a holding time of 2 h, the sample revealed a superior synergy of large strength and good ductility which was related to the formation of spherical fine cementite, heterogeneous deformation-induced strengthening, and recovery of the work-hardening rate mechanism.