Hot-rolled steel sheet for heavy-wall, high-strength line pipe, welded steel pipe for heavy-wall, high-strength line pipe, and method for producing the welded steel pipe

A hot-rolled steel sheet for a heavy-wall, high-strength line pipe,

• the hot-rolled steel sheet having a chemical composition comprising, in mass %,
• C:
• 0.02 to 0.20%,
• Mn:
• 0.80 to 2.10%,
• Si:
• 0.01 to 0.50%,
• P:
• 0.034% or less,
• S:
• 0.0050% or less,
• Nb:
• 0.01 to 0.15%,
• Ti:
• 0.001 to 0.030%, and
• Al:
• 0.001 to 0.080%, the balance being Fe and incidental impurities,
• the hot-rolled steel sheet having a microstructure in which a main phase is a continuous cooling transformation structure and in which {001}α grains in a plane whose normal direction is a sheet width direction constitute an area fraction of 10% or less and have a combined size of 10 μm or less in terms of an area fraction average grain diameter, wherein
• the hot-rolled steel sheet has a tensile strength of 520 MPa or greater, and, in a drop weight tear test (DWTT), a temperature at which a percent ductile fracture reaches 85% is −25° C. or lower.