Abstract: Recently, bainitic rail steel attracts a lot of attention because of its excellent combination of strength and toughness, good weldability and high resistance of wear and fatigue. In general, the multiphase microstructure of bainitic rail steel contains bainitic ferrite, martensite and retained austenite. Bainitic ferrite and martensite have similar body-centered cubic crystal structure, so how to distinguish bainitic ferrite and martensite and quantitatively characterize the microstructure of bainitic rail steel becomes a difficult problem. In this paper, four kinds of experimental metallographic methods, namely, color metallography, electron backscatter diffraction (EBSD), nano indentation and dilatometer methods accompanied with XRD analysis, were employed to distinguish the martensite and bainitic ferrite and to measure their fractions in bainitic rail steel. The results show that the fractions of bainitic ferrite and martensite analyzed by the four methods are similar, with 47.3vol%—53.5vol% of bainitic ferrite, 40.3vol%—46.5vol% of martensite and 6.2vol% of retained austenite (obtained by XRD), respectively. Among the four methods, color metallography is the most convenient and economical method, while EBSD and nano indentation could distinguish more refined microstructural details in multiphase.
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2020, Vol. 34 
