Abstract: Corrosion failure happened to an S32750 duplex stainless steel hexagon head bolt used on the water pump of an enterprise after 2 years of use. The corrosion causes of the bolt were analyzed by macroscopic analysis, scanning electron microscopy and energy spectrum analysis, metallographic analysis, mechanical property test, chemical composition analysis and simulation verification test. The results show that the failure mode of the bolt was pitting corrosion. The root causes of the bolt pitting corrosion were that the improper heat treatment process led to the obvious intermetallic compound σ phase in the microstructure of the bolt, and there was corrosive medium Cl^- in the service environment.