S136钢模具在使用过程中发生早期开裂失效，采用宏观观察、化学成分分析、扫描电镜分析、能谱分析、金相检验等方法对该模具的失效原因进行了分析。结果表明：大件模具开裂的主要原因是，由于内孔电加工脉冲电流过大，内孔边缘产生严重的淬火变质层，造成表面拉向应力开裂；同时基体组织中存在网状碳化物，降低材料强度和韧性，加大模具内孔开裂倾向及裂纹扩展进程。小件模具开裂的主要原因是，由于模具凹槽部位倒角半径过小，应力集中显著增大，在工作载荷的作用下，形成应力集中而开裂。

Early cracking failure of S136 steel molds occurred during its use. The failure causes of the molds were analyzed by means of macro observation, chemical composition analysis, scanning electron microscopy, energy spectrum analysis and metallographic examination. The results show that the main reason for the cracking of large pieces mold was that the excessive pulse current in the electrical machining of the inner hole caused serious quenching and modification layer on the edge of the inner hole, which resulted in the surface tension stress cracking. At the same time, there were reticulated carbides in the matrix structure, which can reduce the strength and toughness of the material, increase the tendency of cracking in the inner hole of the mold and accelerate the process of crack propagation. The main reason for the cracking of small pieces mold was that the chamfer of the groove was too small and the stress concentration increased remarkably. Under the action of working load, stress concentration and cracking were formed.