Fracture analysis of 45 steel bolt

The microstructure,surface fracture morphology,hardness and tensile strength of the failed 45 steel connecting bolt were analyzed and tested.The results show that the outer layer of the failed bolt forehead is the normal microstructure of tempering sorbite,but its core and the screw rod part present the non-normal microstructure of ferrite network and pearlite,which is the main reason to reduce the hardness,strength and toughness of the bolt steel.In addition,no transition arc was machined from the bearing surface of the bolt forehead to the neck scapular root of the screw rod,which leds to the bolt fracture failure also.