Preparation and Mechanical Properties of Nano/Ultrafine Bainitic Structure in AISI 52100 Steel

The development of nano/ultrafine bainitic structure in AISI 52100 steel was the goal of this study. For this purpose, the AISI 52100 the specimens were austenitized at 1050 °C for 60 min followed by low temperature austempering treatment at different temperatures and times. The austempered samples were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and tension test. According to achieved results, the microstructure of AISI 52100 steel after the austempering treatment consisted of ultrafine bainitic ferrite plates and retained austenite with two morphologies of micrometer-block and fine film. At the austempering temperature up to 250 °C, the micrometer-blocky morphology of austenite completely vanished from the microstructure, and the strength and ductility increased to about 2000 MPa and 7 %, respectively. By increasing the austempering temperature to 300 °C, the strength and ductility reduced (to about 1808 MPa and 3 %) simultaneously as a result of changing in the shape and size of bainite phase.