由美国进口牌号为E52100、线径为1.6 mm的轴承钢盘圆, 加工成小型精密轴承零件, 经中性盐浴热处理并在圆端面磨削到成品要求后, 被磨削的表面出现了极细小的黑色凹坑, 凹坑数量及位置无规律可循。经光学显微镜和扫描电镜观察及X射线能谱分析后发现, 在E52100轴承钢材料基体内部存在着大小不等、形状各异、位置不确定的异常组织颗粒, 这些颗粒均含有较高含量的氧元素, 为氧化物夹杂;在磨削过程中, 这些硬而脆的氧化物颗粒极易从基体中剥落而出现凹坑; 这些非金属氧化物夹杂是轴承钢材料中原有的, 与盐浴热处理无关。

Little black surface pits were found on the surface of minor precision bearing parts which made of E52100 bearing steel disk with diameter of 1.6 mm and imported from USA after neutral salt bath heat treatment and finishing mill, and there was no regularity for number and position of the surface pits. Formation reason for the pits was studied by means of optical microscope, scanning electron microscope and X-ray energy dispersive spectrometer. The results show that there were many abnormal granular particles with different sizes, shapes and locations in material of the bearing parts. These particles were oxide inclusions which had high oxygen content and easy to fall off from the substrate and form the surface pits because of its high hardness and brittlement during finishing mill process. These nonmetallic oxide inclusions were innate in the imported E52100 bearing steel and it had nothing to do with the salt bath heat treatment.