STEEL SHEET AND LINE PIPE STEEL PIPE EXCELLENT IN HYDROGEN-INDUCED CRACK RESISTANCE AND TOUGHNESS

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet that is excellent in hydrogen-induced crack resistance and toughness by sufficiently suppressing the fine HIC of about severalμm, particularly in the steel sheet surface layer portion where the hydrogen concentration is high and the environment is severe.SOLUTION: A steel sheet excellent in hydrogen-induced crack resistance and toughness is characterized in that: it comprises regular elements and the balance consists of iron and inevitable impurities; the ratio of Ca amount to S amount (Ca/S) is 2.0 or more, and also the ratio of the maximum Ca concentration (Cmax) in the area to a depth of 5 mm from the surface in sheet thickness direction, to the average Ca concentration (Cave) in said area (Cmax/Cave) is 1.20 or less.