Intergranular Cracking Mechanism of 1Cr17Ni2 Brake Lever Bolt in High-speed Train

Intergranular cracking occurred to a brake lever bolt of 1Cr17Ni2 martensitic stainless steel in a high-speed train. The cracking mechanism was studied by fracture observation, corrosion products analysis, mechanical tests, microstructure observation and verification tests. The results show that the intergranular cracking of the bolt mainly resulted from two aspects. The internal cause is that the grain boundary strength was weakened because of the segregation of Cr element on the grain boundary caused by the unreasonable tempering treatment and the generation of the bead-like second-phase Cr-containing particles on the grain boundary. The external cause is that the bolt was under the external force with high strain rate during service. Furthermore, the crack initiation position revealed that stress concentration also played an important role in cracking of the brake lever bolt.