Method for manufacturing high chromium system seamless steel pipe

摘要

A method for manufacturing a high Cr system seamless steel pipe having a high inside surface quality with a high efficiency and at a reduced production cost is provided. An initial material including Cr at a content of 10 to 20%, and impurities S and P at respective contents of not more than 0.050% is used to form a finished pipe, and when using parameters, the total soaking period SIGMAt1 (hours) for soaking the initial material to form a primary pipe material as a billet or bloom and the total soaking period SIGMAt2 (hours) for soaking the primary pipe material, a finished pipe is formed at a heating temperature of 1,200° C. under the condition that the following equation (b) is satisfied: 1 $\begin{array}{cc}F=f+0.6x\left(1-\frac{1}{e^{\sum it\mathrm{t1}}}\right)+0.8x\left(1-\frac{1}{e^{\sum \mathrm{t2}}}\right)>-9.7& \left(b\right)\end{array}$ where f is a factor indicating the degree of generating the delta ferrites in accordance with the contents of elements included therein. The method allows a high Cr system seamless steel pipe having a very small amount of inside surface defects to be formed, using a high Cr steel. Since a predetermined productivity can be attained without any excessive addition of impurities, a high Cr system seamless steel pipe having a high inside surface quality can be produced with a high efficiency.