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≡(W_Cr+3.3W_Mo+16W_N)/W_Mn

• • where W_Cr is Cr content (% by mass), W_Mo is Mo content (% by mass) W_N is N content (% by mass) and W_Mn 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

[0068] The high-nitrogen austenitic stainless steel of this invention can be worked so as to produce wire product or sheet product. In this case, a more distinct level of strengthening is available by carrying out the area-reducing process at the final stage of the wire making or sheet making by cold wire drawing or cold rolling. After such process, Cr-base nitride having a diameter of 2 μm or larger is observed neither in the section of a wire product 100, shown in FIG. 1, normal to the axis thereof, nor in the section of a sheet product 150, shown in FIG. 2, normal to the drawing direction thereof, and it is made possible to obtain the wire product or sheet product as having a mean grain size (in circle-converted diameter) of the austenitic matrix phase of 100 μm or smaller. The refinement of the mean grain size of the austenitic matrix phase makes it possible to obtain the wire product or sheet product having an extremely high strength and an excellent corrosion resistance. A specific attainable level of strength may be 1,500 MPa or more, or may be even 2,000 MPa or more (strengthening up to 2,500 MPa or around, for example, is attainable, with the upper limit value not specifically limited).

[0069] The finally-obtained grain size of the austenitic matrix phase of the wire product or sheet produ

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 th

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