采用宏观检验、金相检验、硬度测试及断口分析等方法, 对万能工具磨床用大顶尖产生淬火开裂的原因进行了分析。结果表明: 顶尖淬火开裂具有热应力型应力引起大型非淬透件形成纵劈和横断的特征。主要是顶尖中心部位的疏松、非金属夹杂物以及网状碳化物的存在降低了材料的脆断强度, 淬火时热应力中的切向和轴向最大拉应力超过材料的脆断强度引起了顶尖开裂。

The reasons of quenching cracking in the big sustain top used in the universal grinder were analyzed through macroscopic inspection, metallographic examination, hardness testing and fracture analysis. The results showed that the cracking had the characteristics of longitudinal cracking and cross-sectional cracking in the large non-hardened parts. The critical reason was that there were loose, nonmetallic inclusions, serious netted carbide in the central of big sustain top, which weakened the strength of fragile split. The maximal shearing and axial tensile stress exceed the strength of fragile split when sustain top was quenched, which resulted in the longitudinal cracking and cross-sectional cracking.