Patent ID: 7396421
Filing Date: 2008-07-08
Classification: C22C

Abstract:
1. A duplex stainless steel containing, by mass %, C: not more than 0.03%, Si: 0.01 to 2%, Mn: 0.1 to 2%, P: not more than 0.05%, S: not more than 0.001%, Al: 0.003 to 0.05%, Ni: 4 to 12%, Cr: 18 to 32%, Mo: 0.2 to 5%, N (nitrogen): 0.05 to 0.4%, O (oxygen): not more than 0.01%, Ca: 0.0005 to 0.005%, Mg: 0.0001 to 0.005%, Cu: 0 to 2%, B: 0 to 0.01%, and W: 0 to 4%, and the balance of Fe impurities, where a number of oxide-based inclusions, which have a total content of Ca and Mg of 20 to 40% by mass and also have a long diameter of not less than 7 μm, is not more than a 10 per 1 mm 2 of the cross section perpendicular to the working direction, wherein a pitting resistance index PREW represented by the following equation (1) is not less than 40: wherein each chemical symbol represents the content of each element (% by mass).