| 摘要 |
<p>The purpose of the present invention is to provide a high-strength thick-walled electric-resistance-welded steel pipe having both excellent low-temperature toughness and HIC resistance, and having a yield strength of at least 400 MPa. In the present invention, a steel raw material including, by mass%, 0.025-0.084% C, 0.10-0.30% Si, and 0.70-1.80% Mn, the content of P, S, Al, N, and O being adjusted, further containing 0.001-0.065% Nb, 0.001-0.065% V, 0.001-0.033% Ti, and 0.0001-0.0035% Ca, and satisfying a Pcm of 0.20 or less is subjected to hot rolling at a draft of at least 20% in the non-recrystallization temperature range after being heated to and held in a temperature range of 1200-1280°C. After hot rolling is completed, the steel raw material is cooled to a cooling stop temperature of 630°C or below at a cooling rate of 7-49°C/s, and is wound into a hot-rolled strip at 400°C to less than 600°C. The hot-rolled steel strip is roll formed and electric-resistance welded to obtain an electric-resistance-welded steel pipe, and a welded part of the electric-resistance-welded steel pipe is furthermore subjected to thermal processing in which the welded part is heated so that the entire wall thickness reaches a temperature range of 800°C-1150°C, and is then cooled to 630°C or below at an average cooling rate of 7-49°C/s. A high-strength thick-walled electric-resistance-welded steel pipe is thereby obtained in which both the parent material and the electric-resistance-welded part have excellent toughness and HIC resistance.</p> |
