Formation and Exfoliation of the White Etching Layer of D2 High Speed Wheel Steel under Sliding Wear

The surface morphology and microstructure observation and analysis of D2 high speed wheel steel after sliding wear at different rotations were carried out to study the formation, development and exfoliation of the white etching layer and the connection between them. The results show that the wear mechanism of the test block gradually changed from adhesive wear to abrasive wear with the increase of the number of sliding wear rotations, Formation of a nanocrystalline white etching layer on the worn surface was observed. The white etching layer was composed of ferrite nanocrystalline and a small amount of cementite particles. The mechanism of formation was plastic deformation mechanism. Based on observation of the cross sectioned surface, formation process of the white etching layer included five steps: 1) The crescent-shaped plastic deformation layer appeared in the wear furrow, and the ferrite was refined; 2) The formation of a relatively uniform severe plastic deformation layer on the worn surface, cementite was broken into short rod or even granular; 3) Formation of the white etching layer with the thickness of less than 1 μm in the furrow, its inner structure was nano-sized ferrite and cementite small particles; 4) Thicker crescent-shaped white etching layer in furrows; 5) Crescent-shaped white etching layer in adjacent furrows were interconnected to a thickness of 10 μm. The exfoliation process of the white etching layer was as follows. The crack initiation was generated mainly at the ridge. The surface cracks extended and met in the furrow along the direction of 30°~45° with the friction force in the subsurface along the interface of the white etching layer and deformation layer, and finally produced layered surface metal or exfoliation of foil (with the white etching layer).