Influence of inclusions on initiation of pitting corrosion and stress corrosion cracking of X70 steel in near-neutral pH environment

In-situ 2D and 3D microscopic technologies are used to analyze the influence of inclusions on pitting and stress corrosion cracking initiation of X70 steel in near-neutral pH solution. The chemical dissolution of complex oxide inclusions or part of them induces corrosion pits. Circular protected region forms around Ds inclusions due to dissolution of CaS. The Si-enriched inclusions remain intact, but interstice forms at the inclusion/matrix interface due to the dissolution of the matrix. Both complex oxide inclusions and Si-enriched inclusions can induce initiation of SCC micro-cracks, but most of the micro-cracks are generated inside the ferrite grains.