Investigation of stress corrosion cracking of the cast and forged steel in water

Abstract

The aqueous stress corrosion behavior of cast steel and forged steel of the same heat has been examined. It was shown that the activation energy of crack growth of both cast and forged steels was identical,i.e., Q = 5540 cal/mol, and was comparable with the apparent diffusion activation energy of hydrogen in the steel. Theda/dt for cast and forged steel increased under both cathodic and anodic polarization conditions. Correspondingly, the steady-state hydrogen permeation flux increased steeply with the increase of polarizing current under either cathodic or anodic polarization. The influences of the polarization upon theda/dt and the hydrogen permeation flux were similar. TheK _ISCC of the cast steel was larger than that of the forged steel. This may be due to the observation that the steady-state permeation flux for the forged steel was twice as large as that of the cast steel. For both cast and forged steels the fracture modes were clearly dependent uponK _I at the crack tip, and a transition from dimple to quasi-cleavage or intergranular was observed on the fracture surfaces with decreasingK _I .