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

Abstract

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