The feasibility of substituting 30CrMnSiA bolt with M thread by TC4 bolt with MJ thread is testified. In experiments

the tensile properties of 30CrMnSiA bolts are superior to TC4 bolts while the fatigue properties of TC4 are better than 30CrMnSiA bolts. The fractographic analysis is done to make certain that the rupture is fatigue destroy. The process of bolt manufacture is considered. The residual press and MJ thread which generate from the rolling process are the main factors which effect the fatigue performance of bolt.