Cracking due to Cu and Ni segregation in a 17-4 PH stainless steel piston rod

The 17-4 PH stainless steel is employed to produce piston rods in industry due to the high strength and toughness, good workability and nice corrosion resistance. In the present failure analysis, obvious long cracks were observed along the longitudinal direction on the surface of the commercial 17-4 PH stainless steel piston rod after heat treatment. The cracks were carefully looked into by observing the crack tip and characterizing the microstructure along the cracks. The results showed that the cracks were mostly initiated from the surface of the rod and propagated along the phase boundary between martensite and delta ferrite. The EDXA showed that the segregation of Cu and Ni should be responsible for the cracking after heat treatment. In order to define when the crack was coming into being, oxidation film along the crack was considered as a clue. The scrutiny of the oxidation film on the crack edge illustrated that the crack should be formed right in the heat treatment of aging. (C) 2016 Elsevier Ltd. All rights reserved.