Study on the mechanism for polygonisation formation of D2 wheel steel and its effect on microstructure and properties under rolling wear conditions

The rolling wear experiments of D2 wheel steel were carried out on the friction and wear machine. The forming mechanism of polygonisation on the sample surface and the influence of polygonisation wear on microstructure and hardness were studied by using contour measuring instrument, acceleration sensor, SEM (with EBSD) and microhardness tester. The results indicate that the polygonisation of the sample surface is mainly caused by the vertical vibration of the system and wear coupled under the rolling wear conditions. The development process of crest surface wear is from the initial adhesive wear to oxidation wear and adhesive wear, and finally to oxidation wear with a small amount of fatigue wear. The trough surface wear is fatigue wear, which is gradually intensified. After forming the polygonisation, the surface of crest and trough will respectively produces rolling-sliding contact with different creep rate. The wear mode changes from uniform wear to severe wear, and the wear of trough is more significantly serious than that of crest. During the formation of the polygonisation, the proportion of high angle grain boundary (HAGB) in the pre-eutectoid ferrite at the subsurface of crest and trough increased obviously, the grain refinement is more serious, and the hardness extreme or platform appears. The highest hardness is always on the surface. However, the surface hardness of the crest is similar to that of the unformed polygonisation, and the surface hardness of the trough continues to increase with the development of the polygonisation.