METHOD OF PRODUCING SEAMLESS STEEL TUBE

PROBLEM TO BE SOLVED: To provide a method of producing a seamless steel tube of 17Cr steel having suppressed flaw of an outside surface and an inside surface of a steel tube.SOLUTION: The seamless steel tube is provided that contains, by mass%, C:0.06% or less, S:0.005% or less, Cr:15.5 to 18.0%, Ni:2.5 to 6.0%, Si:1.0% or less, Mn:0.01 to 2.0%, P:0.05% or less, Al:0.001 to 0.1%, Cu:1.0 to 3.5%, N:0.06% or less, V:0 to 0.3%, Ca:0 to 0.05% and B:0 to 0.01%, the content of Mo and W satisfying formula (1). A method of producing a seamless steel tube is provided that comprises a step 2 of heating a billet at a soaking temperature of 1260 to 1300°C for in-furnace time of 8 hours or less in a heating furnace with an oxygen concentration of atmosphere in the furnace of 0.2 vol.% or less and a step S3 of performing piercing rolling on the heated billet. 1.0≤(Mo+0.5×W)≤3.5... (1)SELECTED DRAWING: Figure 4 【課題】鋼管の外面及び内面の疵を抑制した１７Ｃｒ鋼の継目無鋼管の製造方法の提供。【解決手段】質量％で、Ｃ：０．０６％以下、Ｓ：０．００５％以下、Ｃｒ：１５．５〜１８．０％、Ｎｉ：２．５〜６．０％、Ｓｉ：１．０％以下、Ｍｎ：０．０１〜２．０％、Ｐ：０．０５％以下、Ａｌ：０．００１〜０．１％、Ｃｕ：１．０〜３．５％、Ｎ：０．０６％以下、Ｖ：０〜０．３％、Ｃａ：０〜０．０５％及びＢ：０〜０．０１％を含有し、かつＭｏ及びＷの含有量が式（１）を満たす継目無鋼管。炉内雰囲気の酸素濃度が０．２体積％以下である加熱炉において、１２６０〜１３００℃の均熱温度及び８時間以下の在炉時間でビレットを加熱する工程Ｓ２と、加熱されたビレットを穿孔圧延する工程Ｓ３とを含む継目無鋼管の製造方法。１．０≦（Ｍｏ＋０．５×Ｗ）≦３．５・・・（１）【選択図】図４