Cracking Cause of Plane Seat 1Cr17Ni2 Austenitic Stainless Steel Outer Nut

1Cr17Ni2 austenitic stainless steel outer nuts of a plane seat guide cracked after 1 000–2 000 h service. The cracking cause of the nut was analyzed by macroscopic morphology observation, fracture macro and micro morphology observation, microstructure observation and hardness detection. The results show that the outer nut underwent stress corrosion cracking. The internal cause of cracking included chain distribution of chromium precipitates at grain boundaries and high content of δ-ferrite and plastic inclusions in structure of outer nut, leading to the high hardness and brittleness. The external cause included corrosive chlorine environment and certain assembly stresses.