It was found that the broach was locally overheated due to band segregation of carbide, and under-tempered.These factors caused fracture of broach as a result of high internal stress.

• 严重的碳化物带状偏析,使拉刀产生局部淬火过热和回火不足,造成内应力急剧增高,最终导致拉刀断裂。