Microstructure evolution and wear resistance of high silicon bainitic steel after austempering

Abstract

The microstructure, hardness, impact toughness and ring block wear properties of a novel bainitic steel were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal microscopy (LCM), X-ray diffraction (XRD), Rockwell hardness tester, impact tester and MM-200 wear tester (Jinan Sida Testing Technology Co., LTD, China). The above steel was austenitized at 900 °C, and was isothermally quenched at 250, 280, 310, 340, 370, 400 and 430 °C respectively. The results showed that the microstructure of the bainitic steel was mainly composed of bainitic ferrite (BF), retained austenite (RA), and martensite/austenite (M/A). A part of the RA underwent a phase transition and transformed into martensite during the wear process, resulting in the increase of the hardness. The wear morphology of bainitic steel was dominated by straight furrows. The wear mechanisms were mainly abrasive wear and oxidative wear. With the increase of the austempering temperature, the microstructure coarsened, the amount of the blocky RA content increased, the hardness of the high silicon bainitic steel increased slightly first and then decreased, the impact toughness improved significantly first and then reduced, and the wear resistance increased first and then decreased. Under the same test conditions, the high silicon bainitic steel after austempering at 340 °C had better combination of hardness and toughness, stable and low friction coefficient, and excellent wear resistance.