Effect of gas quenching rate on microstructure and hardness of SAE 1078 steel during austempering treatment

The patenting process is required to obtain the proper ductility and toughness of high carbon steel for subsequent cold forming by wire drawing or rolling. It is mainly used with lead media for patening treatment because the excellent heat transfer properties of lead achieve uniform temperature distribution. Replacing this process with technology that eliminates the use of hazardous lead presents challenges. In this study, our goal is to investigate the relationship between microstructure changes and mechanical properties according to isothermal temperatures and cooling rates using garnet powder as an alternative to lead media. After the austenizing treatment, the microstructure, hardness and friction properties of patented specimens at three isothermal temperatures (460, 560, 660 °C) and three compressed air flow rates (10, 50, 100 l/min) were analyzed to examine the relationship between mechanical properties according to lamellar spacing in pearlite. As the isothermal temperature decreases or the air flow rate increases, not only the lamellar spacing of perlite decreases, but also the banite structure is formed, which improves the hardness and wear characteristics.