Effect of Patenting Condition on the Microstructure and Hardness of SAE 1078 Steel during Austempering Treatment

Abstract

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 medium for patenting 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 patenting condition (isothermal temperatures and cooling rates) using mixed powder as an alternative to lead medium. After the austenitizing 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 pearlite decreases, but also the bainite structure is easy to form, which improves the hardness and wear characteristics.