Steel Material Suitable For Use In Sour Service Environment

Abstract: Provided is a steel material that has high yield strength and excellent fracture toughness in low-temperature sour service environments. The steel material of the present disclosure has the chemical composition set forth in the description, a yield strength sYS of at least 758 MPa, and a molybdenum content ?Mo in the vicinity of prior austenite grain boundaries in the steel material of at least 5.0 mass%. Furthermore, if the yield strength sYS is less than 862 MPa, the steel material of the present disclosure has an Fn1, defined by formula (1), of at least -300 and, if the yield strength sYS is 862 MPa or greater, the steel material of the present disclosure has an Fn1, defined by formula (1), of at least -520. Formula (1): Fn1 = 83 × (?Mo-10-7×v?) - sYS, where ?Mo in formula (1) represents the molybdenum content in the vicinity of prior austenite grain boundaries in mass%, ? in formula (1) represents the dislocation density in m-2, and sYS in formula (1) represents the yield strength in MPa.

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