Method of mitigating stress corrosion cracking in austenitic solid solution strengthened stainless steels

Abstract

A method of providing resistance to intergranular stress corrosion cracking in an alloy material, the method comprising sensitizing the alloy to form carbides, allowing the carbides to precipitate, and applying a heat treatment to replenish a chromium-depleted zone.

1 . A method for providing resistance to intergranular stress corrosion cracking in an Fe—Ni—Cr alloy material, the method comprising:
 sensitizing the Fe—Ni—Cr alloy material with a heat treatment to form carbide precipitates at grain boundary interfaces and chromium-depleted zones about the carbide precipitates; and   extending the heat treatment of the sensitized Fe—Ni—Cr alloy material for a time effective to allow diffusion of chromium into a chromium-depleted zone;   wherein the carbide precipitates, in combination with the diffusion of chromium into the chromium depleted zones provide resistance to intergranular stress corrosion cracking.   
     
     
         2 . The method of  claim 1 , wherein the Fe—Ni—Cr alloy material comprises at least 16% chromium. 
     
     
         3 . The method of  claim 1 , wherein sensitizing and the heat treatment of the Fe—Ni—Cr alloy material is at a temperature from about 450° C. to 700° C. 
     
     
         4 . The method of  claim 1 , wherein sensitizing the Fe—Ni—Cr alloy material comprises a welding process. 
     
     
         5 . The method of  claim 1 , wherein the carbide precipitates comprise chromium. 
     
     
         6 . The method of  claim 1 , wherein the carbide precipitates are of the formula Cr 23 C 6 , Cr 7 C 3  and combinations thereof. 
     
     
         7 . The method of  claim 6 , wherein the carbide precipitates further comprise Mo, V, W, Ti, Nb, Ta, Hf, and combinations thereof. 
     
     
         8 - 10 . (canceled) 
     
     
         11 . The method of  claim 1 , wherein the heat treatment is extended for a period of time in a range of about 10 to about 3000 hours. 
     
     
         12 - 14 . (canceled) 
     
     
         15 . The method of  claim 1 , wherein the alloy material comprises a 800 series or 300 series stainless steel. 
     
     
         16 . The method of  claim 15 , wherein the alloy material further comprises one or more additional alloying elements. 
     
     
         17 . The method of  claim 16 , wherein the one or more additional alloying elements comprise vanadium, aluminum, tungsten, cobalt, copper, nitrogen, carbon and combinations of these. 
     
     
         18 . The method of  claim 1 , wherein the method provides the alloy material with resistance to stress corrosion cracking. 
     
     
         19 . A method for providing resistance to stress corrosion cracking in a sensitized Fe—Ni—Cr alloy material having carbide precipitates at grain boundary interfaces and a chromium depleted zone about the carbide precipitates, the method comprising:
 Heating the sensitized Fe—Ni—Cr alloy material to a temperature and a time effective to diffuse chromium from a grain matrix of the Fe—Ni—Cr alloy material into the chromium depleted zone, wherein the carbide precipitates, in combination with the diffusion of chromium into the chromium depleted zones provide resistance to intergranular stress corrosion cracking.   
     
     
         20 . The method of  claim 19 , wherein the alloy material is an 800 series alloy. 
     
     
         21 . (canceled) 
     
     
         22 . (canceled)