Ferritic-austenitic stainless steel excellent in corrosion resistance and workability andmethod of production of same

Abstract

The present invention relates to ferritic-austenitic stainless steel oriented to have low Ni which is excellent in corrosion resistance, particularly in corrosion resistance in a neutral chloride environment, and has high “uniform elongation”—a factor governing workability—and a method of production for the same.There are independently provided ferritic-austenitic stainless steels and methods of production for the same particularly having a corrosion resistance in a neutral chloride environment satisfyingPI value(=Cr+3Mo+10N—Mn)≧18% and having a uniform elongation satisfying−10≦Md≦110 (where Md=551−462({C}+[N])−9.2[Si]−8.1[Mn]−13.7[Cr]−29[Ni]−29[Cu]−18.5[Mo], where [ ] is composition (mass %) in the austenite phase, and { } is average composition (mass %))

Description

TECHNICAL FIELD[0001]The present invention relates to ferritic-austenitic stainless steel excellent in corrosion resistance and workability and a method of production of the same. According to the present invention, it is possible to produce ferritic-austenitic stainless steel excellent in corrosion resistance and workability without including a large amount of the expensive and rare element of Ni, so it is believed this can contribute to resource conservation and environmental protection.BACKGROUND ART[0002]Stainless steel may be broadly divided into austenitic stainless steel, ferritic stainless steel, and two-phase (ferritic-austenitic) stainless steel. Austenitic stainless steel contains expensive Ni in 7% mass or more. Many types are excellent in workability. Ferritic stainless steel contains almost no Ni and generally has considerably lower workability than austenitic stainless steel. On the other hand, two-phase (ferritic-austenitic) stainless steel has a comparatively small ...

AI Technical Summary

Benefits of technology

[0016]The present invention was made in view of the current state of the prior art and has as its object to provide ferritic-austenitic stainless steel oriented at lower Ni which is excellent in corrosion resistance, particularly corrosion resistance in a neutral chloride environment, and which has a high “uniform elongation”, the factor governing workability, and a method of production of the same.

[0017]The inventors engaged in intensive research to solve the above problems and as a result discovered that by defining the ingredients and metal structure of the steel, particularly the balance of the ferrite phase and austenite phase, and controlling the annealing conditions and other production conditions, ferritic-austenitic stainless steel which has a corrosion resistance in a neutral chloride environment equal to or greater than SUS 304, which has excellent uniform elongation, and which is excellent in corrosion resistance and workability can be obtained and thereby completed the present invention.

[0023](4) Ferritic-austenitic stainless steel excellent in corrosion resistance and workability as set forth in any of (1) to (3), characterized by having a pitting potential Vc′100 in a 30° C., 3.5% NaCl aqueous solution of 0.3V (Vv.s.AGCL) or more.

Problems solved by technology

Ferritic stainless steel contains almost no Ni and generally has considerably lower workability than austenitic stainless steel.

However, ferritic stainless steel is very inferior to austenitic stainless steel with respect to workability, particularly in material elongation and uniform elongation.

Further, it contains several percent of Mo—which is rarer and more expensive than Ni.

Therefore, there is still a problem in terms of spread of use and economy.

However, if the uniform elongation does not increase, the actual workability will not improve.

Further, even if steel sheet or plate does not break and “fracture” in actual shaping, it is often judged unworkable when necking occurs.

However, even these citations do not describe at all the uniform elongation which governs the actual workability.

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