Effect of microstructure on corrosion resistance of a martensitic stainless linepipe material was surveyed from viewpoint of sulfide stress cracking (SSC) and carbon dioxide (CO2) corrosion. SSC test resulted that steel having more retained austenite showed higher SSC resistance. In the steels containing 10% or more retained austenite, even a large amount of fresh martensite was not harmful to SSC. The more retained austenite containing samples showed lower strengths, but it was difficult to explain the SSC resistance only by the strength. The corrosion resistance in pure CO2 corrosion environment was not significant different among various microstructure. In very mild sour environment, which contained slight
amount of hydrogen sulfide, the corrosion rate of steels containing higher retained austenite showed slightly higher value than the others.
Key words: Martensitic stainless, Linepipe, Retained austenite, Fresh martensite, Tempered martensite, Sulfide stress cracking