Influence of heat treatment process on the microstructure and hardness of Q345B steel

Abstract This paper studied and determined the heat treatment processing technology of Q345B steel, and analyzed its metallographic structure and hardness after different quenching and tempering methods. The results showed that the salt quenching cooling rate was the fastest, resulting in the most martensite and the highest hardness. The hardness of salt-quenched, water-quenched, and oil-quenched steel decreased sequentially, but all of them are significantly higher than the initial hardness of Q345B steel. 950°C was more suitable for quenching Q345B steel than 900°C, with better microstructure and hardness. After quenching, tempering is conducted, and under the same quenching process, three different types of tempering are conducted. The hardness of low-temperature tempering, medium-temperature tempering, and high-temperature tempering decreased sequentially, but they were not lower than the initial hardness of Q345B steel.