Two-phase stainless steel and manufacturing method therefor

Abstract

The purpose of the present invention is to expand application to steel types having corrosion resistance of SUS329J1 or greater. The present invention addresses the problem of obtaining a two-phase stainless steel that both exhibits excellent corrosion resistance in environments with high chloride-ion concentration close to that of brackish water or seawater, and is economically advantageous. Theinventors found that the effect of improving critical pitting temperature (CPT) was likely to be achieved when a minute amount of Nb was added after reducing the amount of Mn to less than 2.0%, and Nto no more than 0.25%. The steel augmented with the minute amount of Nb was subjected to a solid-solution heat treatment, and on determining how depositions of Cr nitride and Nb nitride were affectedthereby, the inventors developed a two-phase stainless steel made of a base material having improved corrosion resistance. When the ratio between the Cr amount [Cr] and the Nb amount [Nb] in extraction residue is brought to 0.2 or greater by controlling the depositions of the chrome nitride and the niobium nitride through gradual cooling to 800 degrees centigrade followed by quick cooling to 600 degrees centigrade, the corrosion resistance can be improved.

Description

technical field [0001] The present invention relates to a duplex stainless steel material exhibiting excellent corrosion resistance in an environment close to brackish water or seawater with a high chloride ion concentration, and a method for producing the same. Background technique [0002] Duplex stainless steel contains a large amount of Cr, Mo, Ni, and N, and intermetallic compounds and nitrides tend to precipitate, so solution heat treatment at 1000°C or higher is performed to solid-solve the precipitates. Recently, an alloy element-saving duplex stainless steel has been developed that saves Ni, Mo, etc., contains Mn, and greatly reduces the precipitation sensitivity of intermetallic compounds. [0003] In alloying element-sparing duplex stainless steels, the main influencing precipitates are chromium nitrides. Chromium nitride is a precipitate combined with Cr (chromium) and N (nitrogen). In duplex stainless steel, it is mostly cubic CrN or hexagonal Cr 2 N precipita...

AI Technical Summary

Problems solved by technology

However, these stainless steels are relatively expensive, and it is necessary to further improve the economical efficiency in order to expand the application as a general-purpose steel.

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