42CrMo高强螺栓热处理开裂原因分析

采用金相显微镜检测了 42CrMo螺栓断口的显微组织，比较了不同断裂区形貌的差别，并分析了钢中带状组织与裂纹产生间的关系。结果表明： 42CrMo螺栓心部存在的孔洞和裂纹等缺陷影响螺栓的强度，但螺栓淬火开裂的原因是淬火应力集中；螺栓横断面近中心区、放射区和瞬断区的韧性存在差别，瞬断区为韧性断裂，而近中心区为解离和沿晶脆性断裂；螺栓近中心区存在带状组织，碳化物含量高的带状组织降低钢材韧性，易萌生拉拔裂纹，成为淬火开裂源。

Cracking analysis of 42CrMo high strength bolt after heat treatment

Microstructures of the 42CrMo bolt fracture were examined by metallographic microscope. The differences of morphology in different fracture zones were compared. And the relationship between the banded structure and crack initiation in steel was analyzed. The results showed that the defects such as holes and cracks in the core of the 42CrMo bolt affected the strength of the bolt，but the quenching stress concentration was the reason for the cracking of the bolt. There were differences in the toughness of the bolt cross section near the central zone，radial zone and instantaneous fault zone. It was ductile fracture in instantaneous fault zone，and it were dissociated and intergranular brittle fracture near cente zone. The banded structure existed near central part of the bolt，and the banded structure with high carbide content would reduce the toughness of steel and be easy to initiate drawing crack，which became the source of quenching cracking.