J-integral based fracture toughness of 15Cr–5Ni stainless steel during phase transformation

This paper proposes a simple effective method to extract the elastoplastic toughness J1C from a simple experiment on a plate. The method is based on a combination of global experimental load displacement measurements, finite element simulation, and digital image correlation which is used to observe the crack propagation initiation as well as to determine the appropriate boundary conditions to be used in numerical simulation. This method is applied to obtain the J1C value of material 15Cr–5Ni stainless steel, which is normally written as 15–5PH after different temperature histories. This paper investigates the influence of the different material state history on the mechanical properties due to the heat treatment and possible phase transformation. Meanwhile, the fractography is also analysed. The result of J1C value shows that the pure martensite 15–5PH has higher fracture toughness at room temperature than at 200 °C. The toughness is also higher than the original material after one cycle heat treatment, which is probably caused by some residual austenite. Meanwhile, pure austenite 15–5PH has a higher fracture toughness than pure martensite 15–5PH at 200 °C. The J1C value of the dual phase 15–5PH during the martensitic transformation also shows that possibly austenite can enhance the ductility of the material as well as fracture toughness.