Analysis of Different Types Fracture Surface of a High Strength Bolt

The 10.9 grade bolts made of SCM435 steel were subjected to overload, fatigue and hydrogen embrittlement fracture. Combined with the macro and micro morphology, the formation mechanism of different fracture types of bolt surfaces were studied. The results show that each fracture surface occurred in the thread part, and the micro characteristics were obvious. The overload fracture surface shows the characteristics of dimple, and the dimple of the screw fracture surface of the blind hole was shear dimple. The fatigue fracture surface had bright fatigue lines, the fatigue area of high and low cycle fatigue fracture surface accounted for 2/3 and 1/2 of the whole section. The grain of hydrogen embrittlement fracture surface was clear and the characteristics of intergranular fracture were obvious. Among different types of fracture surfaces, tightening+stretching fracture surfaces necking and thread elongation were the most obvious, the high and low cycle fatigue fracture surfaces basically had no necking and elongation, and the other types of thread fracture surfaces had a slight elongation.