Influence of carbon on stress corrosion cracking of high strength pipeline steel

• A surface solid carburization process was applied to X80 pipeline steel.
• Anodic dissolution occurred on the ferrite grains rather than carbon-rich structures.
• Galvanic effect induced micro-cracks at the junction of anode/cathode.
• Coalescence of micro-cracks and ferrite grain dissolution may lead to TGSCC.
• Higher crack velocity at grain boundaries and grain passivation may induce IGSCC.

To understand the influence of carbon on stress corrosion cracking of pipeline steels, a carburization treatment was applied to API X80 steel. Carbon-rich structures rather than ferrite grains remain intact and act as cathode during immersion in the acidic environment. Coalescence of micro-cracks induced by galvanic effect and higher dissolution inclination of ferrite grains lead to the higher driving force for crack growth within grains in the low pH environment. Higher average crack velocity at grain boundaries and passivation of ferrite grains provide higher driving force for crack propagates along grain boundaries in the high pH environment.