Fracture failure analysis on ultra supercritical turbine bolts

Fracture failure analysis on ultra supercritical turbine bolts was carried out by means of chemical composition analysis, mechenical properties testing, metallographic examination and fracture analysis. The results show that the main reason of the bolts fracture is high temperature stress-rupture, with the fracture morphology being intergranular cracking character. The main fracture is perpendicular to the axial direction of bolt, which indicates that the tensile working stress result in the crack. In addition, another kind of cracks which is 45ºof the axis has been found on the bolt. It indicates that there must be some abnormal torsion stress on the bolt which most possibly be caused during assembling process.