Development of a Heat Treating Process for 9254 Steel Used to Create the Winning Entry in the 2022 Heat Treating Society Strong Bar Competition

Abstract

This paper summarizes the development of a heat-treating process developed by an undergraduate student team competing in the 2022 Heat Treating Society Strong Bar Competition. The objective of the competition was to heat treat a 10 mm diameter rod of 9254 steel to realize the highest strength possible (with a minimum hardness of 50 HRC) while maintaining sufficient ductility to achieve at least 4 mm of deflection during a 3-point bend test. The process selected was a modified martempering heat treatment to achieve the desired properties. The modified martemper consisted of austenitizing the sample at 870 °C for twenty-five minutes and then quenching in corn oil held at a temperature of 200 °C. The sample remained immersed in the oil for three minutes and then air cooled to 100 °C. When the sample hit 100 °C, it was immediately tempered at 200 °C followed by air cooling to room temperature. Properties of the steel were measured on samples in four conditions: as received, as quenched, martemper + 450 °C tempering for two hours, and martemper + 200 °C temper for one hour. The heat treatment that resulted in the best properties was the martemper with the 200 °C temper for one hour. The average hardness for this method was 54.0 HRC, which met all requirements for the competition. The sample properties during a 3-point bend test were a maximum bend strength of 41.3 kN and a deflection of 8 mm. Post bend testing analysis of the microstructure of the competition sample revealed an internal crack approximately 0.1 mm in length. This paper describes the competition and the methods used by the student team to develop the heat treating process.