High-nitrogen austenitic stainless steel

Abstract

This invention provides a high-nitrogen austenitic stainless steel superior to the conventional one both in the corrosion resistance and strength, despite a low Ni content, characterized in having a Fe content of 50% by mass or more; containing Cr: 15.0% by mass to 35.0% by mass, Mo: 0.05% by mass to 8.0% by mass %, Mn: 0.2% by mass to 10.0% by mass, Cu: 0.01% by mass to 4.0% by mass and N: 0.8% by mass to 1.5% by mass, both ends inclusive, having a C content of 0.20% by mass or less, a Si content of 2.0% by mass or less, a P content of 0.03% by mass or less, a S content of 0.05% by mass or less, a Ni content of 0.5% by mass or less, an Al content of 0.03% by mass or less, and an 0 content of 0.020% by mass or less; wherein the contents of Cr, Mo, N and Mn are adjusted so that a compositional parameter η expressed by the equation: η≡(WCr+3.3WMo+16WN) / WMn where WCr is Cr content (% by mass), WMo is Mo content (% by mass) WN is N content (% by mass) and WMn is Mn content (% by mass) has a value of 5 or above. and optionally further containing either one of, or both of: W: 0.01% by mass to 1.0% by mass; and Co: 0.01% by mass to 5.0% by mass, both ends inclusive; and optionally further containing at least one of: Ti: 0.01% by mass to 0.5% by mass; Nb: 0.01% by mass to 0.5% by mass; V: 0.01% by mass to 1.0% by mass; and Ta: 0.01% by mass to 0.5% by mass, both ends inclusive; and optionally further containing at least one of: B: 0.001% by mass to 0.01% by mass; Zr: 0.01% by mass to 0.50% by mass; Ca: 0.001% by mass to 0.01% by mass; and Mg: 0.001% by mass to 0.01% by mass, both ends inclusive; and optionally further containing either one of, or both of: Te: 0.005% by mass to 0.05% by mass; and Se: 0.01% by mass to 0.20% by mass, both ends inclusive.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to a high-nitrogen austenitic stainless steel. [0003] 2. Description of Related Art [0004] Austenitic stainless steel represented by SUS304, SUS316 and so forth are widely used as a steel excellent in corrosion resistance and workability. For purposes demanding particularly excellent corrosion resistance and strength at the same time, SUS316 as an austenitic stainless steel, and SUS329 as a dual-phase stainless steel are generally used. For applications demanding still more excellent corrosion resistance, there is also used SUS836L (also referred to as “super-austenitic stainless steel”) having Ni and Mo contents increased therein to a considerable degree. [0005] The above-described austenitic stainless steels, generally believed as highly corrosion resistant, can however show only a limited resistance against local corrosion, and this raises a further demand on still higher strength. Large am...

AI Technical Summary

Benefits of technology

[0037] The high-nitrogen austenitic stainless steel of this invention makes it possible to attain a good balance between the strength and corrosion resistance, by allowing a large amount of N (nitrogen) to solubilize while limiting Ni content, and by optimizing contents of the essential elements which comprise Cr, Mo, N and Mn within ranges specific to this invention. This consequently makes it possible to realize a high-nitrogen austenitic stainless steel superior to conventional one both in the corrosion resistance and strength, despite a low Ni content. For example, it is no more impossible to achieve both of high corrosion resistance equivalent to that of SUS836L which is a super-austenitic stainless steel, and strength higher than that of SUS329J4L which is a dual-phase stainless steel, after being subjected to solution heat treatment.

[0070] As has been described in the above, the high-nitrogen austenitic stainless steel of this invention is successful in achieving both of high corrosion resistance equivalent to that of SUS836L which is a super-austenitic stainless steel, and strength higher than that of SUS329J4L which is a dual-phase stainless steel, after being subjected to solution heat treatment. The steel can realize a strength of as high as 1,500 MPa or more (or even as high as 2,000 MPa or more), when cold-worked in a form of wire product or sheet product after the solution heat treatment.

Problems solved by technology

The above-described austenitic stainless steels, generally believed as highly corrosion resistant, can however show only a limited resistance against local corrosion, and this raises a further demand on still higher strength.

Adoption of such high Mn composition may result in a degraded corrosion resistance, and also in an insufficient strength.

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