Corrosion pitting resistant martensitic stainless steel and method for making same

Abstract

A method of making a forged, martensitic, stainless steel alloy is provided. The alloy is a forged preform of martensitic, pitting corrosion resistant stainless steel alloy comprising, by weight: 12.0 to 16.0 percent chromium; greater than 16.0 to 20.0 percent cobalt, 6.0 to 8.0 percent molybdenum, 1.0 to 3.0 percent nickel, 0.02 to 0.04 percent carbon; and the balance iron and incidental impurities. The alloy has a microstructure that comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure. The method heats the preform to a solutionizing temperature to form a solutionized microstructure. The preform is cooled with a liquid to room temperature. The preform is immersed in a cryo-liquid to transform the retained austenite phase in the microstructure to martensite. The preform is heated to a temperature of less than 600° F. for a time sufficient to form a tempered forged preform.

1 . A forged, martensitic, stainless steel alloy comprising, by weight:
 about 12.0 to about 16.0 percent chromium;   greater than 16.0 to about 20.0 percent cobalt;   about 6.0 to about 8.0 percent molybdenum;   about 1.0 to about 3.0 percent nickel;   about 0.020 to about 0.040 percent carbon;   and the balance iron and incidental impurities; and   wherein the alloy has a microstructure that comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure.   
     
     
         2 . The alloy of  claim 1 , wherein the microstructure comprises about zero percent by volume of a sigma phase. 
     
     
         3 . The alloy of  claim 2 , wherein the microstructure includes no sigma phase. 
     
     
         4 . The alloy of  claim 1 , wherein the microstructure contains about zero percent by volume of a laves phase, a chi phase, and a delta ferrite phase. 
     
     
         5 . The alloy of  claim 4 , wherein the microstructure contains no laves phase, no chi phase, and no delta ferrite phase. 
     
     
         6 . The alloy of  claim 1 , wherein the alloy comprises a turbine airfoil preform or a compressor airfoil preform. 
     
     
         7 . A forged, martensitic, stainless steel alloy comprising, by weight:
 about 12.0 to about 16.0 percent chromium;   greater than 16.0 to about 20.0 percent cobalt;   about 6.0 to about 8.0 percent molybdenum;   about 1.0 to about 3.0 percent nickel;   about 0.020 to about 0.040 percent carbon;   and the balance iron and incidental impurities; and   wherein the alloy has a microstructure that comprises about zero percent by volume of a sigma phase.   
     
     
         8 . The alloy of  claim 7 , wherein the microstructure includes no sigma phase. 
     
     
         9 . The alloy of  claim 7 , wherein the microstructure comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure. 
     
     
         10 . The alloy of  claim 7 , wherein the microstructure contains about zero percent by volume of a laves phase, a chi phase, and a delta ferrite phase. 
     
     
         11 . The alloy of  claim 10 , wherein the microstructure contains no laves phase, no chi phase, and no delta ferrite phase. 
     
     
         12 . The alloy of  claim 7 , wherein the alloy comprises a turbine airfoil preform or a compressor airfoil preform. 
     
     
         13 . A forged, martensitic, stainless steel alloy comprising, by weight:
 about 12.0 to about 16.0 percent chromium;   greater than 16.0 to about 20.0 percent cobalt;   about 6.0 to about 8.0 percent molybdenum;   about 1.0 to about 3.0 percent nickel;   about 0.020 to about 0.040 percent carbon;   and the balance iron and incidental impurities; and   wherein the alloy has a microstructure that comprises about zero percent by volume of a sigma phase, and wherein the alloy microstructure comprises a retained austenite phase less than or equal to 2 percent by volume of the microstructure.   
     
     
         14 . The alloy of  claim 13 , wherein the microstructure includes no sigma phase. 
     
     
         15 . The alloy of  claim 13 , wherein the microstructure contains about zero percent by volume of a laves phase, a chi phase, and a delta ferrite phase. 
     
     
         16 . The alloy of  claim 15 , wherein the microstructure contains no laves phase, no chi phase, and no delta ferrite phase. 
     
     
         17 . The alloy of  claim 13 , wherein the alloy comprises a turbine airfoil preform or a compressor airfoil preform.