Influence of Tempering on Microstructure and Mechanical Property of Si-Mn-Mo Bainite Steel

The influence of tempering at different temperature on microstructure and mechanical property of Si-Mn-Mo bainitic steel after quenching is studied in laboratory.It is found that strength and plasticity of this steel can be significantly improved through tempering after quenching.Mechanical properties of the bainitic steels tempered at 300℃ or 350℃after quenching are similar while the strength and hardness is reduced and toughness and plasticity is slightly improved after tempering at 450℃.The microstructure of the bainitic steel is composed of bainitic ferrite and residual austenite(flaky and blocky M-A island).Tempering properly after quenching can accelerate the decomposition of the M-A island,so percentage composition of the bainitic ferrite lath is increased and the stability of residual austenite can be improved.Thus,the stability of microstructure and mechanical property of this steel is improved.