Ultra High Strength Alloy for Severe Oil and Gas Environments and Method of Preparation

Abstract

A high strength, corrosion resistant alloy suitable for use in oil and gas environments includes, in weight percent: 0-15% Fe, 18-24% Cr, 3-9% Mo, 0.05-3.0% Cu, 4.0-6.5% Nb, 0.5-2.2% Ti, 0.05-1.0% Al, 0.005-0.040% C, balance Ni plus incidental impurities and deoxidizers. A ratio of Nb/(Ti+Al) is equal to 2.5-7.5.

1 - 17 . (canceled) 
     
     
         18 . A high strength, corrosion resistant alloy suitable for use in oil and gas environments, comprising in weight %: 0-15% Fe, 18-24% Cr, 3-9% Mo, 0.05-3.0% Cu, 4.0-6.5% Nb, 0.5-2.2% Ti, 0.05-1.0% Al, 0.005-0.040% C, balance Ni plus incidental impurities and deoxidizers, wherein a ratio of Nb/(Ti+Al)=2.5-7.5. 
     
     
         19 . The alloy of  claim 18 , wherein the maximum Fe content is 12%. 
     
     
         20 . The alloy of  claim 18 , wherein the minimum Mo content is 3.5%. 
     
     
         21 . The alloy of  claim 18 , wherein the minimum Cu content is 0.1%. 
     
     
         22 . The alloy of  claim 18 , wherein the minimum Cu content is 1.0%. 
     
     
         23 . The alloy of  claim 18 , wherein the minimum Ti content is 0.6%. 
     
     
         24 . The alloy of  claim 18 , wherein the minimum Ti content is 0.8%. 
     
     
         25 . The alloy of  claim 18 , wherein the maximum Al content is 0.7%. 
     
     
         26 . The alloy of  claim 18 , wherein the C content is less than 0.030%. 
     
     
         27 . A bar or tube suitable for use in oil and gas wells made of the alloy of  claim 18 . 
     
     
         28 . A method of making a high strength, corrosion resistant alloy comprising the steps of:
 (a) providing the alloy of claim  1  in ingot form;   (b) hot working the ingot to a desired shape; and   (c) heat treating the shaped alloy by: (i) providing a first solution annealing by heating at between 1750° F. (954° C.) to 2050° F. (1121° C.) for a time of about 0.5-4.5 hours, followed by a water quenching or air cooling; (ii) aging by heating to a temperature of at least about 1275° F. (691° C.) and holding at that temperature for a time of between about 6-10 hours to precipitate γ′ and γ″ phases; optionally (iii) providing a second aging heat treatment at about 1050° F. (565° C.) to 1250° F. (677° C.) and holding at that temperature to conduct a secondary aging step for about 4-12 hours, then air cooling after aging to ambient temperature.   
     
     
         29 . The method of  claim 28 , wherein step (a) includes: vacuum induction melting plus vacuum arc remelting the alloy prior to step (b). 
     
     
         30 . The method of  claim 28 , wherein the heating time of the first solution annealing step (c) (i) is about 1 hour and the holding time in secondary aging step (c) (iii) is about 8 hours. 
     
     
         31 . A bar or tube suitable for use in in oil and gas wells made according to the method of  claim 18 .