STEEL PLATE WITH EXCELLENT HYDROGEN-INDUCED CRACKING RESISTANCE AND TOUGHNESS OF THE WELD HEAT AFFECTED ZONE, AND STEEL TUBE FOR USE AS LINE PIPE

摘要

A steel plate with excellent hydrogen-induced cracking resistance and toughness of the weld heat affected zone (HAZ toughness) and a steel pipe obtained using the steel plate are achieved. The steel plate is characterized to contain specified elements with the remainder consisting of iron and inevitable impurities, in which the ratio of Ca amount and S amount (Ca/S) is 2.0 or more, Ca amount, S amount, and O amount satisfy (Ca-1.25S)/O‰¤1.8, and, in a region from the surface to 5 mm depth in the plate thickness direction, Ca-based inclusions with 50 µm or more of the long diameter or long side are 2.0 pieces/mm 2 or less, and TiN with 300 nm or less of the long diameter or long side is 5×10 2 pieces/µm 2 or more.