Failure Analysis on Fracture of Grade 4.8 Philips Screw

The fracture of philips screw with strength grade demand of 4.8 happened in assembly process, and four of them and another two inventory screws were checked and analyzed. The results show that the fracture reason of screw 1 and screw 2 was the oxide inclusions under the cross counterbore formed in cold heading,and the fracture reason of screw 3 and screw 4 was the cracks at the thread root because of improper rolling process. In addition, the irregular thread shape of screw 3 was also an important reason for the fracture.