HIGH-STRENGTH STEEL SHEET AND HIGH-STRENGTH WELDED STEEL PIPE EXCELLING IN DUCTILE FRACTURE PERF0RMANCE AND PR0CESS F0R PR0DUCING THEM

摘要

The present invention to a tensile strength of providing a ductile fracture properties are excellent high-strength steel sheet and high-strength welded steel pipe corresponding to the X100 grade, and methods for their preparation of the API specifications, in mass%, C: 0.01 to 0.5%, Si: 0.01 to 3%, Mn: 0.1 to 5%, P: 0.03% or less, S: it made by containing 0.03% or less, and the balance of Fe and unavoidable impurities, to 1 in area ratio, including the 60% of ferrite and the balance of Bay and night and having a microstructure consisting of martensite, by rolling in the axial direction of the plate, the maximum value of the density of the {100} cross-sectional thickness was 20 to 50˚ rotation from the end of 3 or less, as measured by ultrasonic flaw detection plate method high strength welded steel pipe for high strength steel sheet excellent in the ductile properties and the steel sheet, characterized in that the thickness is less than 1 ㎜ parallel cracks in the base material. ; Ductile, high strength, ferrite, crack parallel to the thickness