Influence of thermomechanical processing and heat treatments on tensile and Charpy impact properties of B and Cu bearing high-strength low-alloy steels

High-strength low-alloy steels containing different B and Cu contents were fabricated by thermomechanical processing and heat treatments such as accelerated cooling, intercritical annealing, and tempering, and then tensile and Charpy impact tests were conducted on them in order to investigate the mechanical properties in terms of yield strength, deformability, and toughness. The test results revealed that the B-added acceleratedly cooled specimens composed mostly of lath martensite had relatively high yield strength, poor deformability and low-temperature toughness in contrast to the B-free acceleratedly cooled specimens consisting mainly of granular bainite and degenerate upper bainite. When the B-added acceleratedly cooled specimens were tempered, the yield strength increased to a certain degree and the low-temperature toughness was remarkably improved, but the deformability severely deteriorated. However, the B-added intercritically annealed specimens provided an attractive balance of yield strength, deformability, and low-temperature toughness due to the dual-phase microstructure of fine ferrite and martensite with lath type morphology.