Fracture Analysis of Bolt Made of GH4033 Superalloy

The slide valve bolt in a catalytic unit fractured during service, leading to the falling off of the valve body guide rail and the valve plate. The fracture cause of the GH4033 bolt was determined by macroscopic observation, chemical composition analysis, microstructure examination, fracture analysis and microscopic observation. The results show that the facture of the bolt is intergranular brittle fracture caused by high temperature creep damage. Improper heat treatment causes coarse grain in the bolt, and less second phase and intergranular carbide, which weaken the fine grain, the second phase and the grain boundary strengthen, leading to the decline of creep property. Long-term service at high temperature led to creep damage and micro-crack initiation, and damage accumulation accelerated the formation and expansion of crack, resulting in the early fracture of the bolt.