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| Cracking analysis of 42CrMo high strength bolt after heat treatment |
| LI Xia1， ZHU Shi-li2， JIN Man-jie1 |
1.Zhonghang Monitoring Technology Research Institute Co.，Ltd.，Hangzhou 310022，China
2.Manufacturing Management Department，Ningbo Iron and Steel Co.，Ltd.，Ningbo 315807，China |
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Abstract 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.
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Received: 02 April 2019
Published: 15 December 2019
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2019, Vol. 37 
