Study on the surface microstructure evolution and wear property of bainitic rail steel under dry sliding wear

Abstract

As the industry of railway transportation is thriving, much more attention has been paid to the properties of wheel/rail steel materials. Although conventional wheel/rail steel materials have proved their competence so far, it is necessary to think ahead and develop new wheel/rail steel materials in order to meet new challenges raised by railway transportation in the future. Since bainitic steel is the first choice for the new wheel/rail steel material, it is especially important to fundamentally investigate its wear property. Through the sliding wear experiment on AB1 bainitic rail steel, the microstructural evolution of bainitic steel during the wear process and the factors that affected its wear property were probed into in this paper. Under sliding wear, it was discovered that ploughing wear, adhesion wear and flake-like peeling were the primary morphological characteristics of AB1 bainitic rail on the worn surface, and the flakes generated by peeling were relatively thin; WELs appeared on the worn surface of AB1 bainitic rail steel, with the thickness of less than 20μm. The main microstructure inside the WELs contained nanoscale bainitic ferrite grains and martensite grains. Under the impact of stress, the surface microstructure of AB1 bainitic rail steel underwent the following changes: the direction of bainitic ferrite laths gradually became perpendicular to that of the stress, and with the increase of the deformation strain and strain rate, bainitic ferrite laths were segmented into numerous short bar-shaped subgrains and even into nanoscale equiaxed grains with random orientations; residual austenite, no longer stable, underwent martensite transformation, and after the formation of martensite, under the influence of pressure stress, martensite lath grains were multidirectionally segmented into pieces that formed nanoscale martensite grains. Residual austenite inside the microstructure of AB1 bainitic rail steel, the thickness of bainitic ferrite laths and the WELs formed during the wear process would all affect the wear property of bainitic steel.