Hot-rolled steel sheet for thick-walled high-strength line pipe, welded steel pipe for thick-walled, high-strength line pipe, and manufacturing method thereof

摘要

Suitable for transportation pipelines of natural gas, crude oil, etc., especially API X60-X80 grade high strength (yield strength YS: 415 MPa or more, tensile strength TS: 520 MPa or more), DWTT characteristics (brittleness) of the base material To provide a hot-rolled steel sheet for thick-walled, high-strength line pipes with excellent fracture propagation stopping performance. To provide a welded steel pipe for a thick-walled high-strength line pipe using the hot-rolled steel sheet and a method for producing the same. 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 %, Nb: 0.01 to 0.15%, Ti: 0.001 to 0.030%, Al: 0.001 to 0.080%, and the component composition comprising the balance Fe and inevitable impurities The {001} α grains having a continuous cooling transformation structure (Zw) as the main phase and the sheet width direction as the normal direction have an area fraction of 10% or less and a connected size of area average particle diameter. For a thick-walled high-strength line pipe having a microstructure of 10 μm or less, a tensile strength of 520 MPa or more, and a temperature at which the ductile fracture surface ratio is 85% or less in a drop weight test (DWTT) Hot rolled steel sheet.