Steel and component of structural equipment for use in a hydrogen gas environment, and a method for the manufacture thereof

Abstract

A steel which does not suffer from hydrogen embrittlement contains 0.3-30% of Cr as the base material, and has an oxide film having a thickness of 100 nm or more formed on its surface. The oxide film contains at least two elements selected among Fe, Cr and Al in the form of oxides, respectively in an amount of 5 atom % or more. The oxide film is formed through single-step or two-step heating wherein the steel is heated in the atmosphere at 600-900° C. for not less than 3 minutes but not more than 2 hours if necessary, and then heated in a hydrogen atmosphere at 700-1200° C. for not less than 3 minutes but not more than 2 hours while controlling the water vapor partial pressure within the range from 10−8 to 10−1 MPa. The steel is adapted for use in hydrogen gas environments, such as a container or other hardware.

Description

TECHNICAL FIELD [0001] This invention relates to a steel which can be used in a hydrogen gas environment, to a method for its manufacture, and to vessels, piping, and accessories made from the steel. More particularly, it relates to a steel which does not undergo hydrogen embrittlement when used in a hydrogen gas environment, particularly when exposed to a high pressure hydrogen gas environment of 35 MPa or above, and to a method for its manufacture, and to components of structural equipment such as gas cylinders, piping, valves, or other equipment and to accessories therefor which are exposed to a high pressure hydrogen gas environment and which are used in fuel cell automobiles or hydrogen gas stations. BACKGROUND ART [0002] Fuel cell automobiles obtain electric power using hydrogen and oxygen as fuels, and they are attracting attention as the next generation of clean automobiles which do not discharge harmful substances such as carbon dioxide (CO2), nitrogen oxides (NOx), or sulf...

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Benefits of technology

[0008] The object of the present invention is to provide a steel which does not undergo hydrogen embrittlement even when used in a hydrogen gas environment and a method for its manufacture, and a vessel used in high pressure hydrogen gas or other components of structural equipment made from this steel.

[0010] It is known to form a Cr oxide film having a thickness from several nm up to at most 100 nm on the surface of gas piping or components of stainless steel used in semiconductor manufacture in order to decrease the discharge and dissolving out of impurities.

[0016] However, such surface modification has the advantage that it can exhibit a protective action regardless of types of the base material, and the present inventors focused on surface modification so as to suppress penetration of hydrogen into steel and to prevent hydrogen embrittlement. As a result of diligent investigation of types of film having a protective action for preventing permeation of hydrogen, they unexpectedly found that by performing heat treatment in a hydrogen atmosphere containing a controlled steam partial pressure after heat treatment in air or without first performing such heat treatment, if a compound oxide film containing at least two of Fe, Cr, and Al in the form of an oxide is formed to at least a desired thickness, the effect of preventing permeation of hydrogen is exhibited, and penetration of hydrogen into the steel and therefore hydrogen embrittlement of the steel can be prevented.

[0019] It was also found that from the standpoint of preventing hydrogen permeation, in contrast to the conventional theory of forming an oxide film, it is desirable to provide a compound oxide film having a complicated, fine structure. In particular it was found that a compound oxide film having a prescribed content of Fe, Cr, and Al has the greatest effect on preventing hydrogen permeation.

[0020] Namely, when it is desired to obtain a chemical protecting action, it is desirable to form a chemically stable Cr oxide film or Al oxide film as a single phase as much as possible and to avoid intermixing therein of oxides such as Fe oxides or Mn oxides. However, in order to obtain a physical protective action for preventing hydrogen permeation, it is preferable to have a compound oxide film with a complicated and fine structure. In particular, a compound oxide film containing a prescribed amount of Fe, Cr, and Al in the form of oxides provides the greatest effect of preventing hydrogen permeation.

Problems solved by technology

When steel is used in a hydrogen gas environment and particularly a high pressure hydrogen gas environment, there is concern of the problem of the hydrogen embrittlement caused by penetration of hydrogen into the steel.

However, in research performed in recent years, it has been confirmed that hydrogen embrittlement can occur in a specific hydrogen gas environment such as a high pressure hydrogen gas environment even with a low alloy steel or with an austenitic stainless steel for which it was thought to be more difficult for hydrogen embrittlement to occur compared to ferritic stainless steel.

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