| 摘要 |
In the conventional art, it is difficult to stably adjust the strength of a heavy wall steel pipe to a target strength of 95 to 140 ksi (= TS: 655 to 965 MPa) by one Q-T operation. Specifically, a method for manufacturing a heavy wall steel pipe includes a cooling step in which a steel pipe, with a wall thickness of 1/2 inch or more, that has been heated to the gamma range (i.e., austenite region) is dipped in water while supporting and rotating the steel pipe about the axis of pipe, an axial stream which is a water flow in the direction of axis of pipe is applied to the inside surface of the steel pipe under rotation in the water, and an impinging stream which is a water flow impinging on the outer surface of the pipe is applied to the outer surface of the steel pipe under rotation in the water. The rotation is performed at a circumferential velocity of pipe of 4 m/s or more, the application of the axial stream and the impinging stream is started within 1.1 s after the entire steel pipe is dipped, and continued until the temperature of the steel pipe is decreased to 150°C or lower, the pipe flow velocity of the axial stream is set at 7 m/s or more, and the discharge flow velocity of the impinging stream is set at 9 m/s or more. |
