Fracture Analysis on Thread Rolling Screws of Automobile Steering Wheel

The fracture reasons of fixing screws of automobile steering wheel were investigated by means of fracture analysis, metallographic examination, microhardness testing, chemical composition analysis, hydrogen embrittlement preliminary load test and so on. The results indicated that the fracture model of the screw was hydrogen induced delayed fracture, and the crack originated from the bottom of first tooth. Residual hydrogen in screw, carburized layer on the surface, and stress concentration at the first tooth formed the sensitivity factors of hydrogen embrittlement.