| 摘要 |
A duplex stainless steel which has a chemical composition, in mass %, that C: 0.03 % or less, Si: 0.01 to 2 %, Mn: 0.1 to 2 %, P: 0.05 % or less, S: 0.001 % or less, 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): 0.01 % or less, Ca: 0.0005 to 0.005 %, Mg: 0.0001 to 0. 005 %, Cu: 0 to 2 %, B: 0 to 0.01 %, W: 0 to 4 %, and the balance: Fe and impurities, characterized in that it contains oxide type inclusions having a total content of Ca and Mg of 20 to 40 mass % and having a longer diameter of 7 mum or more in an amount of 10 pieces or less per 1 mm2 of the cross section perpendicular to the working direction, or further in that it contains oxide type inclusions having a content of S of 15 mass % or more and having a longer diameter of 1 mum or more in an amount of 10 pieces or less per 0.1 mm2 of the cross section perpendicular to the working direction. In particular, it is desirable that contents of Cu, B and W are 0.2 to 2 %, 0.001 to 0.01 % and 0.1 to 4 %, respectively.
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