尺寸为7/8英寸钢球由直径φ16.5mm棒料冷冲压成型。为检查钢球表面的缺陷，对其进行热酸洗检查，结果发现钢球的两极位置出现裂纹。通过对钢球原材料及钢球裂纹形状、组织、硬度、化学成分等分析，确定裂纹产生的原因是由于原材料在切断过程中金属产生塑性变形，引起金属内晶粒之间产生滑移，晶粒被拉长形成的加工硬化现象导致的，使材料的强度、硬度升高，塑性、韧性下降产生裂纹缺陷。%Steel ball of size 7/8 inch is made from steel rod with a diameter ofφ16.5mm by cold forming. In order to examine the defects on the surface of the steel ball, hot acid test was performed. Results indicated that there were cracks on the two poles of the ball. The cause of the cracks was determined by analyzing the raw materials of the steel ball as well as the shape, structure, hardness and chemical composition of the cracks. It suggested that the metal underwent plastic deformation in the cutting process. The elongation of the metal crystals and the slip between them led to the strain hardening. The cracks were generated as a result of the increased strength and hardness and the decreased plasticity and ductility.
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