STEEL PLATE FOR LINE PIPES AND STEEL PIPES

摘要

The invention provides a steel for high-strength sour-resistant line pipes which has such excellent HIC resistance as to match with severe HIC resistance performance requisite to sour-resistant line pipes having wall thicknesses of 20 mm or above and steel pipes. A steel which contains by weight C: 0.02 to 0.06%, Si: 0.5% or below, Mn: 0.8 to 1.6%, P: 0.008% or below, S: 0.0008% or below, Al: 0.08% or below, Nb: 0.005 to 0.035%, Ti: 0.005 to 0.025%, Ca: 0.0005 to 0.0035% and further contains at need one or more of Cu: 0.5% or below, Ni: 1% or below, Cr: 0.5% or below, Mo: 0.5% or below and V: 0.1% or below and which has a CP value of 0.95 or below as defined by the formula: CP=4.46C(%)+2.37Mn(%)/6+{1.18Cr(%)+1.95Mo(%)+1.74V(%)}/5+{1.74Cu(%)+1.7Ni (%)}/15+22.36P(%) and a Ceq value of 0.30 or above as defined by the formula: Ceq=C(%)+Mn(%)/6+ {Cr(%)+Mo(%)+V(%)}/5+{Cu(%)+Ni(%)}/15.