Abstract
对摩托车发动机缸头螺栓断裂件进行了CTi失效失析分析。螺栓断裂处材质、硬度、抗拉强度、夹杂物均合格，基体显微组织回火索氏体正常，表面脱碳深度(8.3 um)也符合要求。但螺牙底部有折叠裂纹，不符合GB5779.3对螺牙缺陷的要求。推定以折叠裂纹为起源，而后在使用时裂纹扩展造成断裂。通过正交试验改进了螺纹滚压工艺六参数，消除了螺纹折叠。 A CTi failure loss analysis is made on the motorcycle engine cylinder head bolt fracture. The material, hardness, tensile strength, inclusions in bolt split are qualified; the tempered sorbite of matrix microstructure is normal; surface decarburization depth (8.3 um) also meets the requirements. But there is a crack folded at the bottom of the screw tooth of screw tooth defect, which is not in conformity with the GB5779.3 requirements. Presuming folded crack as the origin, fracture occurs resulting from crack propagation when it is being used. Through the orthogonal experiment, the six parameters of thread rolling technology are improved and the thread folding is eliminated.
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