Analysis on Fracture Reason of IN783 Bolt Applied in Ultra Supercritical Steam Turbine

A pressure regulator valve bolt made by alloy IN783 in a power plant was fractured at the position of bolt waist during operation.Based on macro and micro observation, chemical composition and mechanical property inspection, the fracture reason of bolt was investigated.The results showed that fracture originated from the center hole wall, the main characteristic of fracture was intergranular brittleness morphology, and the fracture mode was brittle fracture caused by stress accelerated grain boundary oxidative (SAGBO);the lower resistance of SAGBO due to aging treatment failure of β phases was the main case of fracture.