Through the analysis of the physical and chemical properties of coupling high-strength bolts,it was found that the chemical composition of the bolt material was conform to the requirements with high level of the strength and hardness.The bolt fracture analysis showed that the bolt fracture was flat with the characteristics of instantaneous brittle fracture.The existence of minor defects in the bolt led to the instantaneous brittle fracture of the high-strength bolt with high notch sensitivity coefficient.Improper tempering technology of bolt material was the reason for the existence of coarse lath martensite and high strength.There is a certain correspondence between hardness and strength.For finished bolts that cannot be tested for strength,the correspondence between hardness and strength should be established and hardness should be taken as the acceptance index.
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