Method for producing high chromium seamless pipe or tube

Abstract

A billet containing, by mass %, 8.0 to 16.0% of Cr with a value represented by the formula of “Cr+4Si−(22C+0.5Mn+1.5Ni+30N)” of not more than 9.0%, wherein the symbols of the elements represent the contents, by mass %, of the elements in the steel, is heated by means of a heating furnace conditioned so as to have a soaking temperature of 1100 to 1300° C. and an in-furnace time (min) of not less than “0.5×Diameter of the billet (mm)”. Thereafter, by means of a centering machine capable of forming a center hole having a diameter of not less than “0.34×Diameter of the billet (mm)” at one end face of the said billet where piercing starts by punch of 60 to 110° punching angle, a center hole is formed at the said face of the billet, followed by piercing and rolling by an inclined roll type piercing mill of not more than 8.0% plug tip draft rate. The thus-produced high-Cr seamless pipe or tube has excellent internal surface properties with minimized internal surface defects.

Description

[0001]This application is a continuation of the international application PCT / JP2007 / 053916 filed on Mar. 1, 2007, the entire content of which is herein incorporated by reference.TECHNICAL FIELD[0002]The present invention relates to a method for producing a high-Cr seamless pipe or tube used for oil or gas wells, for various industrial plants, for building structures, and so on. The present invention relates in particular to a method for producing a high-Cr seamless pipe or tube containing, by mass %, 8.0 to 16.0% of Cr.BACKGROUND ART[0003]High-Cr seamless pipes or tubes containing, by mass %, 8.0 to 16.0% of Cr have been widely used for oil or gas wells, for various industrial plants and for building structures.[0004]In order to effectively produce high-Cr seamless pipes or tubes, it is preferable to use an inclined roll type piercing mill (hereinafter often referred to as a “piercing mill”) in the piercing and rolling process. Specifically, a hollow pipe or tube stock is produced ...

AI Technical Summary

Benefits of technology

[0036]According to the method of the present invention, in producing the high-Cr seamless pipes or tubes containing 8.0 to 16.0% of Cr, the internal fracture flaws among the internal surface defects, which are caused in the piercing and rolling process by a piercing mill, can be suppressed.

Problems solved by technology

However, since the hot workability of high-Cr steel is lower than that of a so-called “common steel”, the piercing and rolling by a piercing mill thereof tends to cause defects on the internal surface of the resulting pipe or tube stock.

Since the said treatment needs a lot of man-hours, it leads to a remarkable reduction in production efficiency.

Further, a deep flaw leads to disposal of the pipe or tube itself, resulting in deterioration of production yield.