Nippon Steel Sumitomo Metal Corporation

Tadashi Kawakami

Tetsuo Yokoyama

Yoshitaka Nishiyama

Kouichi Kuroda

Atsuro Iseda

Kazuhiro Uchida

Takashi Nakashima

Toshihide Ono

Tatsuya Okui

Takuya Hanada

Mikio Yoneyama

Syunichi Ootsuka

Yoshihiro Tatsumi

After an inner wall tube, made of steel or alloy containing not less than 2% of Cr, whose outer surface thereof is machined and/or ground to a thickness of 0.1 mm or more including the scale layer, is inserted into an outer wall tube, made of ferritic steel containing not less than 2% of Cr, in which an oxide scale layer containing Cr and having a thickness of 10 to 30 &#x3bc;m is formed in the inner surface thereof, cold working at an outside diameter reduction rate of 5 to 30% is performed. Similarly cold worked after an inner wall tube having an oxide scale layer on the outer surface thereof, is inserted into an outer wall tube whose inner surface is machined and ground. A double-walled tube made has a uniform gap and an excellent thermal conductivity, and is suitable as materials for SG tubes of future FBR.

Double-walled tube with interface gap and production method therefor

Provided is a production method including: heating a workpiece at a temperature higher than an Atransformation point in a carburizing atmosphere; slowly cooling the workpiece at not more than 70&#xb0; C./Hr down to a temperature T satisfying Formula (1) while maintaining the carburizing atmosphere: A&#x2212;20&#x2267;T(&#xb0; C.)&#x2267;300&#xb0; C. . . . (1); and cooling the workpiece in an oxidizing atmosphere. According to this method, it is possible to efficiently produce a high-carbon chromium bearing steel whose depth of the recarburized layer or the overcarburized layer is within a range from 0 to 0.2 mm, having less machining allowance, and excellent in machinability, using a steel tube after hot tube-making.

High-carbon chromium bearing steel and production method of the same

Growing community of inventors

Tokyo, Japan

Tadashi Kawakami