Highly corrosion-resistant austenite stainless steel and method for producing the same

Abstract

A highly corrosion-resistant austenite stainless steel that, even when exposed to temperatures in a range in which a σ phase is precipitated and corrosion resistance varies greatly, the stainless steel remains corrosion resistant, the steel consisting of, in mass %: C: 0.005 to 0.030%, Si: 0.05 to 0.30%, Mn: 0.05 to 0.40%, P: 0.005 to 0.050%, S: 0.0001 to 0.0010%, Ni: 22.0 to 32.0%, Cr: 19.0 to 28.0%, Mo: 5.0 to 7.0%, N: 0.18 to 0.25%, Al: 0.005 to 0.100%, Cu: 0.05 to 0.50%, W: not more than 0.05%, Sn: 0.0005 to 0.0150%, Co: 0.030 to 0.300%, B: 0.0005 to 0.0050%, Fe as a remainder and inevitable impurities, in which the stainless steel satisfies the following formula (1), an area ratio of σ phase is not more than 1%, and CPT based on ASTM G48 Method C as corrosion resistance property is not less than 60° C. 0.05≤10[% B]+2[% P]+6[% Sn]+0.03[% Si]≤0.20  (1)

1 . A highly corrosion-resistant austenite stainless steel consisting of, in mass %: C: 0.005 to 0.030%, Si: 0.05 to 0.30%, Mn: 0.05 to 0.40%, P: 0.005 to 0.050%, S: 0.0001 to 0.0010%, Ni: 22.0 to 32.0%, Cr: 19.0 to 28.0%, Mo: 5.0 to 7.0%, N: 0.18 to 0.25%, Al: 0.005 to 0.100%, Cu: 0.05 to 0.50%, W: not more than 0.05%, Sn: 0.0005 to 0.0150%, Co: 0.030 to 0.300%, B: 0.0005 to 0.0050%, Fe as a remainder and inevitable impurities, wherein the stainless steel satisfies the following formula (1), an area ratio of a α phase is not more than 1%, and CPT based on ASTM G48 Method C as corrosion resistance property is not less than 60° C.
   0.05≤10[% B]+2[% P]+6[% Sn]+0.03[% Si]≤0.20  (1).
 
 
     
     
         2 . The highly corrosion-resistant austenite stainless steel according to  claim 1 , wherein the stainless steel further includes at least one of Nb: 0.005 to 0.250% and V: 0.005 to 0.250%, and satisfies the following formula (2), and crystal grain size of parent material based on JIS G0511 is in a range of 3.0 to 7.0
   1.2≤100{2([% V]+[% Nb])+6[% B]}*([% N]+[% C]−0.1[% Mn])≤5.0  (2).
   
     
     
         3 . A method for production of the highly corrosion-resistant austenite stainless steel according to  claim 1 ,
 as a heat history after solution heat treatment, a temperature range of 700 to 1000° C. is maintained for 10 to 60 minutes by isothermal holding, cooling, or heating process.   
     
     
         4 . A method for production of the highly corrosion-resistant austenite stainless steel according to  claim 2 ,
 as a heat history after solution heat treatment, a temperature range of 700 to 1000° C. is maintained for 10 to 60 minutes by isothermal holding, cooling, or heating process.