350MW超临界锅炉磨煤机减速机输入轴断裂分析

Fracture Analysis on the Input Shaft of Coal Pulverize Reducer of 350 MW Supercritical Unit

某超临界机组磨煤机输入轴在运行3个月后发生断裂。通过对该轴进行金相检测、化学元素成分检测、力学性能检测、断口宏观和扫描电镜分析后表明,输入轴的金相组织和化学元素组成符合相关技术标准要求;其断口为典型的脆性断口,断裂方式为低周期疲劳脆性断裂。由于该输入轴的表面没有按要求进行渗碳处理,表面硬度低,抗拉强度和屈服强度都低于产品质量证明书的要求,导致裂纹源萌生于轴键槽的受力侧;而键槽的位置设计不合理,加快了断裂的过程。

Fracture occurred after 3 months operation of input shaft of coal pulverize reducer. After the investigation of metallographic examination, composition of chemical elements, mechanical properties, macroscopic examination and SEM, it showed that the metallographic and composition of chemical elements of input shaft meet the relevant technical standards. The fracture was typical brittle fracture; and the fracture mode was low cycle fatigue brittle fracture. As the input shaft of surface was not required for carburization, the surface hardness was low; extension strength and yield strength were below the requirement of product quality certificate, so that the crack source generated on the stressed side of keywayl and the position of key way was poorly designed, which accelerated the fracture.