Austenitic stainless steel

Abstract

An austenitic stainless steel, which comprises by mass %, C: 0.04 to 0.18%, Si≦1.5%, Mn≦2.0%, Ni: 6 to 30%, Cr: 15 to 30%, N: 0.03 to 0.35%, sol. Al≦0.03% and further contains one or more elements selected from Nb≦1.0%, V≦0.5% and Ti≦0.5%, with the balance being Fe and impurities, and among the impurities P≦0.04%, S≦0.03%, Sn≦0.1%, As≦0.01%, Zn≦0.01%, Pb≦0.01% and Sb≦0.01%, and satisfy the conditions P1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}≦0.06 and 0.2≦P2=Nb+2(V+Ti)≦1.7−10×P1 has high strength and excellent resistance to cracking due to grain boundary embrittlement in the welded portion during the use at high temperatures. Therefore, the said steel can be suitably used as materials for constructing machines and equipment, such as power plant boilers, which are to be used at high temperatures for a long period of time.

1 . An austenitic stainless steel, which comprises by mass percent, C; 0.04 to 0.18%, Si: not more than 1.5%, Mn: not more than 2.0%, Ni: 6 to 30%, Cr: 15 to 30%, N: 0.03 to 0.35%, sol. Al: not more than 0.03% and further contains one or more elements selected from Nb: not more than 1.0%, V: not more than 0.5% and Ti: not more than 0.5%, with the balance being Fe and impurities, in which the contents of P, S, Sn, As, Zn, Pb and Sb among the impurities are P: not more than 0.04%, S. not more than 0.03%, Sn: not more than 0.1%, As: not more than 0.01%, Zn: not more than 0.01%, Pb: not more than 0.01% and Sb: not more than 0.01%, and the values of P1 and P2 defined respectively by the following formula (1) and formula (2) satisfy the conditions P1≦0.06 and 0.2≦P2≦1.7−10×P1;
     P 1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}  (1),       P 2=Nb+2(V+Ti)   (2);   
       wherein each element symbol in the formulas (1) and (2) represents the content by mass percent of the element concerned. 
     
     
         2 . An austenitic stainless steel, which comprises by mass percent, C: 0.05 to 0.15%, Si: not more than 1.0%, Mn: not more than 2.0%, Ni: 6 to 13%, Cr: 15 to 25%, N: 0.03 to 0.15%, sol. Al: not more than 0.03% and further contains one or more elements selected from Nb: not more than 1.0%, V: not more than 0.5% and Ti: not more than 0.5%, with the balance being Fe and impurities, in which the contents of P, S, Sn, As, Zn, Pb and Sb among the impurities are P: not more than 0.04%, S: not more than 0.03%, Sn: not more than 0.1%, As: not more than 0.01% Zn: not more than 0.01%, Pb: not more than 0.01% and Sb: not more than 0.01 and the values of P1 and P2 defined respectively by the following formula (1) and formula (2) satisfy the conditions P1≦0.06 and 0.3≦P2≦1.7−10×P1;
     P 1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}  (1),       P 2=Nb+2(V+Ti)   (2);   
       wherein each element symbol in the formulas (1) and (2) represents the content by mass percent of the element concerned. 
     
     
         3 . An austenitic stainless steel, which comprises by mass percent) C: 0.04 to 0.18%, Si: not more than 1.5%, Mn: not more than 2.0%, Ni: more than 13% to not more than 30%, Cr: 15 to 30%, N: 0.10 to 0.35%, sol. Al: not more than 0.03% and further contains one or more elements selected from Nb: not more than 1.0%, V: not more than 0.5% and Ti: not more than 0.5%, with the balance being Fe and impurities, in which the contents of P, S, Sn, As, Zn, Pb and Sb among the impurities are P: not more than 0.04%, S: not more than 0.03%, Sn: not more than 0.1%, As: not more than 0.01%, Zn: not more than 0.01%, Pb: not more than 0.01% and Sb: not more than 0.01%, and the values of P1 and P2 defined respectively by the following formula (1) and formula (2) satisfy the conditions P1≦0.06 and 0.2≦P2≦−1.3−10×P1;
     P 1=S+{(P+Sn)/2+{(As+Zn+Pb+Sb)/5}  (1),       P 2=Nb+2(V+Ti)   (2);   
       wherein each element symbol in the formulas (1) and (2) represents the content by mass percent of the element concerned. 
     
     
         4 . The austenitic stainless steel according to  claim 1 , which further contains, by mass percent, one ore more elements of one or more groups selected from the first to third groups listed below in lieu of a part of Fe:
 First group. Cu: not more than 4%, Mo: not more than 2%, W: not more than 2%, Co: not more than 1%, Ta: not more than 0.1%, Zr: not more than 0.1% and Hf: not more than 0.1%;   Second group: B: not more than 0.012%; and   Third group: Ca: not more than 0.02%, Mg: not more than 0.02% and rare earth element: not more than 0.1%.   
     
     
         5 . The austenitic stainless steel according to  claim 2 , which further contains, by mass percent, one ore more elements of one or more groups selected from the first to third groups listed below in lieu of a part of Fe:
 First group: Cu: not more than 4%, Mo: not more than 2%, W: not more than 2%, Co: not more than 1%, Ta: not more than 0.1%, Zr: not more than 0.1% and Hf: not more than 0.1%;   Second group: B: not more than 0.012%; and   Third group: Ca: not more than 0.02%, Mg: not more than 0.02% and rare earth element: not more than 0.1%.   
     
     
         6 . The austenitic stainless steel according to  claim 3 , which further contains, by mass percent, one ore more elements of one or more groups selected from the first to third groups listed below in lieu of a part of Fe:
 First group: Cu: not more than 4%, Mo: not more than 2%, W: not more than 2%, Co: not more than 1%, Ta: not more than 0.1%, Zr: not more than 0.1% and Hf: not more than 0.1%;   Second group: B: not more than 0.012%; and   Third group: Ca: not more than 0.02%, Mg: not more than 0.02% and rare earth element: not more than 0.1%.