D2高速车轮钢在滑动磨损下的白层形成与剥落

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

通过对不同转数滑动磨损后的D2高速车轮钢进行表面形貌和微观组织观察与分析,研究白层形成、发展与剥落过程以及他们之间的联系.结果表明:随着滑动磨损转数的增加,试块表面磨损方式由黏着磨损逐渐转变为磨粒磨损,同时在磨损表面形成纳米晶白层.该白层由铁素体纳米晶和极少量渗碳体小颗粒组成,其形成机制属于塑性变形机制.从横截面角度观察,白层的形成过程主要分为五个阶段:1)在磨损犁沟内出现月牙形塑性变形层,铁素体发生细化;2)磨损表面形成相对均匀的严重塑性变形层,渗碳体碎化成短棒状甚至是颗粒状;3)犁沟内形成厚度小于1μm的白层,其内组织为纳米级的铁素体和渗碳体小颗粒;4)犁沟内白层增厚成月牙形;5)相邻犁沟内的月牙形白层相互连接,厚度可达10μm.白层剥落过程如下:主要在脊缘处产生裂纹源,表面裂纹沿着与摩擦力成30°~45°方向向犁沟内扩展并交汇,在表层沿着白层与变形层交界处或白层内部扩展,最后使表层金属分层甚至出现金属薄片(含有白层)剥落.

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 1μm 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 10μm.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）.