Steel pipe for line pipe and method of manufacturing the same

A method of manufacturing a steel pipe for line pipe, comprising:

• preparing a hollow shell having a chemical composition of, in mass %:
• C:
• 0.02 to 0.11%;
• Si:
• 0.05 to 1.0%;
• Mn:
• 0.30 to 2.5%;
• P:
• up to 0.030%;
• S:
• up to 0.006%;
• Cr:
• 0.05 to 0.36%;
• Mo:
• 0.02 to 0.33%;
• V:
• 0.02 to 0.20%;
• Ti:
• 0.001 to 0.010%;
• Al:
• 0.001 to 0.100%;
• N:
• up to 0.008%;
• Ca:
• 0.0005 to 0.0040%;
• Cu:
• 0 to 1.5%;
• Ni:
• 0 to 1.5%;
• Nb:
• 0 to 0.05%;
• and balance Fe and impurities;
• quenching the hollow shell such that at least one of a maximum Vickers hardness of a portion between an outer surface of the hollow shell and a depth of 1 mm from the outer surface, and a maximum Vickers hardness of a portion between an inner surface of the hollow shell and a depth of 1 mm from the inner surface is not lower than 310 Hv;
• and
• tempering the quenched hollow shell,
• the chemical composition satisfying Equation (1) below,
• Cr+Mo+V≤0.40 (1),
• wherein each of the chemical symbols in equation (1) is substituted for by the content of the corresponding element in mass %.