HIGH-NITROGEN STAINLESS-STEEL PIPE WITH HIGH STRENGTH, HIGH DUCTILITY, AND EXCELLENT CORROSION AND HEAT RESISTANCE AND PROCESS FOR PRODUCING SAME

WIPO Patent Application WO/2011/096592

A1

Provided is a novel high-nitrogen stainless-steel pipe which is not obtained with any conventional technique, the stainless-steel pipe having high strength, high ductility, and excellent corrosion and heat resistance and being obtained through size reduction of crystal grains and strengthening by slight plastic working besides formation of a gradient structure in which the concentration of solid-solution nitrogen continuously decreases gradually from the surface. Also provided are hollow materials of various shapes and sizes which are formed from the steel pipe and processes for producing the steel pipe and the hollow materials. An austenitic stainless-steel pipe is treated in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel-pipe material to cause nitrogen (N) to be absorbed into the surface of the pipe and diffused into the solid phase, while minimizing the enlargement of crystal grains during the treatment. Thus, a gradient structure is formed, the structure including a part that is close to the surface part of the pipe and has been highly strengthened by the formation of a high-concentration solid solution of N and a part in which ductility gradually increases toward around the center of the cross-section of the pipe as the N concentration decreases. Thereafter, the pipe is subjected to size reduction of crystal grains by utilizing, for example, eutectoid transformation of the austenite phase, thereby greatly improving the elongation (ductility) of the steel pipe. Furthermore, the steel pipe is strengthened by slight plastic working to give a high-nitrogen austenitic stainless-steel pipe having high strength, high ductility, and excellent corrosion and heat resistance. A plurality of the thus-obtained high-nitrogen austenitic stainless-steel pipes of the same quality are disposed one over another so as to result in dimensions, e.g., diameter and wall thickness, according to the use or strength level, and this pipe arrangement is united by adhesion processing through hot drawing, hot rolling, or other method to give a high-nitrogen austenitic stainless-steel pipe or hollow material which has high strength, high ductility, and excellent corrosion and heat resistance and has repetitions of the gradient structure within the wall. This stainless-steel pipe or hollow material can have large or small sizes and be of various kinds, and examples thereof include a hollow material for use as a container for storing high-pressure hydrogen gas which is for fuel cell vehicles (FCVs) and which does not suffer hydrogen gas embrittlement (HGE) in the presence of high-pressure hydrogen gas.

MIURA HARUMATU (JP)
ODA KAZUO (JP)

PCT/JP2011/052962

August 11, 2011

February 04, 2011

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MIURA HARUMATU (JP)
ODA IND CO LTD (JP)
ODA KAZUO (JP)

C23C8/80; B21C37/06; B23K20/00; C23C8/26; C23C8/62

JPH01287249A	1989-11-17
JPS5558354A	1980-05-01
JPS5681658A	1981-07-03
JPS62265186A	1987-11-18
JP2005161118A	2005-06-23
JPS5947080A	1984-03-16
JPS5378966A	1978-07-12
JP2008290104A	2008-12-04
JP2003145225A	2003-05-20
JP2008212947A	2008-09-18
JPH0881752A	1996-03-26

TAKASHI NAKAMURA ET AL., ASSETSU TO ROSETSU, 29 February 1964 (1964-02-29), pages 282 - 284, 301 TO 302

MURATA, YUKIO (JP)
Yukio Murata (JP)

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