采用宏观检验、化学成分分析、硬度检测、金相检验等方法对某H13钢注塑热流道喷嘴在装配过程中发生断裂的原因进行了分析。结果表明：该热流道喷嘴断裂主要是由于零件在氮碳共渗处理时，渗氮层内的氮势过高使其内孔螺牙表层开裂和剥落，造成零件在装配时发生脆性断裂；同时内孔螺纹底槽圆角半径极小，应力集中程度显著增大，增加了零件开裂的倾向；热流道喷嘴外表面的加热带在焊接加工后，未进行去应力退火处理，使材料的强韧性大幅度降低，进一步增加了零件脆性开裂的倾向；热流道喷嘴的设计硬度偏高，虽然材料的强度提高了，但其韧性也会有所降低。最后针对上述断裂原因提出了改进措施。

The causes of fracture occurring in the assembling process of an H13 steel injection molding hot runner nozzle were analyzed by macroscopic test, chemical composition analysis, hardness test, metallographic examination and so on. The results show that the fracture of the hot runner nozzle was mainly caused by the high nitrogen potential in the nitrided layer when it was nitrocarburized which led to the cracking and spalling of the screw surface and resulted in the brittle fracture of the part during assembling. At the same time, the fillet radius of the bottom groove of inner hole screw was very small and the stress concentration degree was greatly increased, which also increased the cracking tendency of the parts. The heating zone on outer surface of the hot runner nozzle was not subjected to stress relief annealing after welding process, which greatly reduced the strength and toughness of the material and further increased the brittle cracking tendency of the parts. The design hardness of the hot runner nozzle was rather high, which could increase the strength, but the toughness of the material was also decreased. Finally, improvement measures were put forward according to the fracture reasons.