Hydrogen embrittlement failure of box-like link-plate

This paper present a failure analysis of box-like link-plate. The failed link-plate is fabricated from 42CrMo steel and the surface of internal hole is demanded to be induction-hardened. Metallographic analyses, tensile test and fractography investigation were conducted in order to determine the causes of failure. The strength and toughness levels of link-plate material are below what is expected. A number of fisheyes were found on the tensile fracture surfaces and a lot of non-metallic inclusions are presented in the centre of fisheyes. Two axial cracks were found on the surface of internal hole of link-plate when performing flaw detection after finishing induction-hardening operating on the surface of internal hole. Radial extending depth of two cracks just corresponds to the depth of induction-hardened layer. Intergranular fracture is predominant micromechanism of the crack in link-plate. Evidences indicate that the failure of link-plate is due to hydrogen. The possible source for hydrogen was introduced during melting and casting process. A great number of non-metallic inclusions in the link-plate material acted as traps of hydrogen.