| 摘要 |
Provided is a high-strength hot-rolled steel sheet for a spiral pipe, the hot-rolled steel sheet having excellent low-temperature toughness. The hot-rolled steel sheet comprises specific components, 0<S/Ca<0.8, and satisfies N-14/48×T1≥0%. When analyzed to a depth from the surface of the steel sheet that is equivalent to 1/2 the sheet thickness, the microstructure of the steel sheet has a proeutectoid ferrite percentage between 3% and 20%, with the remainder being a low-temperature transformation phase. The number-average crystal grain diameter of the entire microstructure is 2.5 µm or less, the area-average grain diameter is 9 µm or less, and the standard deviation of the area-average grain diameter is 2.3 μm or less. Furthermore, when analyzed to a depth from the surface of the steel sheet that is equivalent to 1/2 the sheet thickness, the reflected X-ray intensity ratio {211}/{111} in the {211} direction and the {111} direction at the face parallel to the steel sheet surface is 1.1 or greater. The steel sheet has both high toughness and strength that meets or exceeds the API5L-X80 standard. |
