| abstract |
The object of the present invention is to expand the application to steel types having corrosion resistance above SUS329J1, and the object is to obtain a steel that exhibits excellent corrosion resistance in an environment close to the chloride ion concentration of brackish water or seawater and is economical. Duplex stainless steel. The inventors of the present invention found that by adding a small amount of Nb in addition to reducing Mn to less than 2.0% and reducing N to 0.25% or less, the effect of increasing the pitting temperature CPT can be easily obtained. Furthermore, the effects of solution heat treatment on the precipitation of Cr nitrides and Nb nitrides in steels to which a small amount of Nb was added were clarified, and a duplex stainless steel with improved pitting corrosion resistance of the base material was developed. That is, by slow cooling to 800°C and then rapid cooling to 600°C, the precipitation of chromium nitrides and niobium nitrides is suppressed, and the ratio of the Cr content [Cr] to the Nb content [Nb] in the extraction residue is 0.2 or more. This can improve corrosion resistance. |