high strength pipeline steel and high strength pipeline steel with excellent low temperature toughness

摘要

Disclosed are a steel plate and a steel pipe for use in line pipes that have superior low-temperature toughness and are ideal for steel pipes that are used, for example, in line pipes for the transportation of petroleum, natural gas, and the like. The steel plate and steel pipe comprise, in mass%, 0.03 to 0.08% carbon, 0.01 to 0.5% silicon, 1.5 to 2.3% manganese, 0.001 to 0.05% niobium, 0.0010 to 0.0050% nitrogen, and 0.0001 to 0.0050% calcium; have a limit of no more than 0.015% phosphorus, no more than 0.0020% sulfur, no more than 0.030% titanium, no more than 0.030% aluminum, and no more than 0.0035% oxygen; have a residue comprising iron and obligatory impure elements; fulfill S/Ca 0.5; and furthermore have a limit of a maximum hardness of no higher than 400 Hv for a center segregation section and a length of no longer than 0.1 mm for a non-pressure bonded section.