| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively manufacture a seamless steel pipe for high temperature and high pressure steam transportation, having high temperature and high pressure resisting properties and capable of withstanding transportation of high pressure steam to a greater extent more than conventional one. SOLUTION: A billet, having a composition consisting of 0.05-0.15% C, 0.01-0.50% Si, 0.50-1.50% Mn, <=0.025% P, <=0.008% S, 0.10-0.30% Cr, 0.01-0.10% Al, 0.01-0.12% V, 0.01-0.05% Ti, and the balance Fe with inevitable impurities, is hot-pierced and formed into a seamless steel pipe by not rolling at a finishing temperature not lower than the Ar3 transformation point. The steel pipe is introduced, without delay, into a soaking pit at a temp. of (Ar3 point +50 deg.C) to 1,100 deg.C to undergo soaking treatment, cooled rapidly at >=5 deg.C/sec cooling rate, and successively temperature at a temperature between 550 deg.C and Ac1 transformation point. By this method, the seamless steel pipe for high temperature and high pressure steam transportation, having high strength in a medium temperature region and excellent in weldability, can be manufactured at a low cost.
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