某轴承公司在生产40Cr钢轴承挡圈时，发现有轴承挡圈存在车削硬质点的情况。采用化学成分分析、硬度测试、金相检验等方法对车削硬质点产生的原因进行了分析。结果表明：该40Cr钢轴承挡圈车削硬质点为异金属压入所致，应该是在钢材轧制过程中，生产线的零件紧固不好，遇到轧制过程的外力冲击，使得零件部分脱落，在高速轧制过程中被瞬间压入钢材，最终导致该轴承挡圈产生车削硬质点。

When a bearing company produced the 40Cr steel bearing retainer ring, it was found that there were turning hard points in the 40Cr steel bearing retainer ring. The causes of turning hard points were analyzed by means of chemical composition analysis, hardness test, metallographic examination. The results show that the turning hard points of the 40Cr steel bearing retainer ring were caused by the pressing of dissimilar metals. It should be that during the rolling process of steel, the parts of the production line were not fastened well, and they were impacted by the external force during the rolling process, which made the parts fall off. The parts were pressed into the steel in a moment during the high-speed rolling process, which finally caused the turning hard points of the bearing retainer ring.