Manufacturing method of high-strength steel plate for sour line pipe, high-strength steel pipe for sour line pipe, and high-strength steel pipe using high-strength steel plate for sour line pipe

摘要

To provide a method for manufacturing a high strength steel sheet for sour resistant line pipes, in which increase in hardness at 0.25 mm below a surface of the steel sheet is suppressed while sufficient strength is secured.SOLUTION: The method for manufacturing a high strength steel for sour resistant line pipes includes a process of heating a billet having a predetermined composition and then hot rolling it to form a steel sheet, a first water-cooling process, a reheating process, a subsequent air-cooling process, and a following second water-cooling process. In the first water-cooling step, the hot rolled steel sheet is water-cooled under a predetermined condition. Then in the reheating process, the steel sheet surface is reheated to a reheating temperature of not less than (Ar+10°C) and not more than (Ar+100°C). In the air-cooling process, the air-cooling start temperature at the surface of the steel sheet is set to be equal to the reheating temperature, and the air-cooling finish temperature at a surface of the steel sheet is set to the Arpoint or more and (Ar+40°C) or lower as well as (the reheating temperature-10°C) or less, and the steel sheet is air-cooled. In the second water-cooling process, the steel sheet is water-cooled with the water-cooling start temperature at the surface of the steel sheet being set to be equal to the air-cooling finish temperature and the water-cooling finish temperature being set to a predetermined condition.SELECTED DRAWING: Figure 1A