8407钢汽车模型模具发生早期开裂失效，使汽车模型灯杯定位外缘产生毛边，严重影响了汽车模型的外观质量。为了查找模具开裂的原因，通过宏观检查、化学成分分析、硬度测试、能谱分析、金相检验等方法，对模具的组织和工艺特性进行了检测和分析。结果表明：模具产生开裂的原因是，电加工脉冲电流过大，圆孔内壁产生严重的淬火层，造成拉向开裂；基体受到过热导致组织粗大，材料的强度及韧性降低，进一步缩短了模具的使用寿命。

Early cracking failure occurred to the 8407 steel mould for model cars, so that rough selvedge generated on the outer edge of lamp cup positioning of model cars, seriously affecting the appearance quality of the model cars. In order to find out cracking reasons of the mould, the structure and the technological characteristics of the mould were inspected and analyzed by macroscopic examination, chemical composition analysis, hardness testing, energy spectrum analysis, metallographic examination and so on. The results show that:the cracking reasons of the mould were that the pulse current for electrical processing was too large and a serious quenching layer generated on the inner wall of the hole, resulting in the tensile stress cracking; the matrix structure was bulky because of the overheating, which reduced the strength and toughness of the material and further shorten service life of the mould.