Analysis on Fracture Reasons of SWRCH22A Steel Self-Tapping Screws

Fracture occurred to self-tapping screws of SWRCH22A steel after assembly for one day. The fracture reasons were analyzed through macrographic examination, chemical composition analysis, metallographic inspection, fracture analysis and hydrogen content testing. The results indicate that:the fracture mechanism of screws was delayed brittle fracture induced by hydrogen; the microstructure of screws after heat treatment was mainly tempered martensite and a small amount of residual austenite, and the martensite structure was sensitive to hydrogen brittle; the screws were treated by electroplating, which made the hydrogen content of screws as high as 0.000 49%, and finally caused the delayed brittle fracture of screws induced by hydrogen on the root of thread initiation position where the stress concentrated.