某齿轮磨削后表面产生了裂纹，其中齿顶裂纹为常规的磨削裂纹，而齿根裂纹为纵深较大的非常规磨削裂纹，采用化学成分分析、非金属夹杂物检验、金相检验等方法对裂纹产生的原因进行了分析，并从应力角度对磨削裂纹进行了分类。结果表明：磨削齿轮时进刀量过大使得摩擦应力陡增，在该摩擦应力与热应力的共同作用下材料表面被拉裂，导致该齿轮齿顶、齿根产生裂纹；从致使磨削裂纹产生的主导应力角度将磨削裂纹分为内应力主导的磨削裂纹和摩擦应力主导的磨削裂纹，该齿轮齿顶裂纹属于内应力主导的磨削裂纹，齿根裂纹属于摩擦应力主导的磨削裂纹。

Cracks were produced on the surface of a gear after girnding. The cracks of the gear tooth top were normal grinding cracks, while the cracks of the gear tooth root were unconventional grinding cracks with larger depth. The causes of the cracks were analyzed by means of chemical composition analysis, non-metallic inclusion detection, metallographic examination and so on. And the grinding cracks were classified from the stress point of view. The results show that the friction stress increased sharply by large amount of feed when the gear was grinding, and the surface of the material was cracked under the combined action of the friction stress and thermal stress, resulting in the cracks of the gear tooth top and tooth root produced. The grinding cracks were classified from the angle of dominant stress caused by induced grinding cracks, and the grinding cracks were divided into the grinding cracks dominated by internal stress and the grinding cracks dominated by friction stress. The cracks of the gear tooth top belonged to the grinding cracks dominated by internal stress, and the cracks of the tooth root belonged to the grinding cracks dominated by friction stress.