High temperature alloys

Abstract

An improved nickel-chromium-iron alloy is provided, which comprises up to about 5% of hafnium-containing particles. In one embodiment, an improved creep resistant castable oxide dispersion strengthened nickel-chromium-iron alloy comprises up to about 5% of hafnium, with at least part of the hafnium being present as finely dispersed oxidized particles. Further embodiments of the improved alloy can comprise additionally up to about 15% by weight aluminum. The alloy is particularly useful in the production of creep resistant tubes and castings, for example, for the petrochemical market.

1 . A method for manufacturing an oxide dispersion strengthened nickel-chromium-iron alloy which comprises adding finely divided hafnium particles to a melt of the alloy before pouring, under conditions such that at least part of the hafnium is converted to hafnium oxide particles in the melt. 
   
   
       2 . The method according to  claim 1 , wherein the hafnium particles have a particle size less than 5 mm. 
   
   
       3 . The method according to  claim 2 , wherein the hafnium particles have a particle size less than 4 mm with an average particle size ranging from 1 to 2 mm. 
   
   
       4 . The method according to  claim 1 , in which the alloy is an alloy comprising: 
     
       
         
               
               
               
             
                   
                   
               
                   
                 Carbon 
                 0.01-0.7%   
               
                   
                 Silicon 
                 0.1-3.0%   
               
                   
                 Manganese 
                 0-2.5% 
               
                   
                 Nickel 
                 15-90%   
               
                   
                 Chromium 
                 5-40%  
               
                   
                 Molybdenum 
                 0-3.0% 
               
                   
                 Niobium 
                 0-2.0% 
               
                   
                 Tantalum 
                 0-2.0% 
               
                   
                 Titanium 
                 0-2.0% 
               
                   
                 Zirconium 
                 0-2.0% 
               
                   
                 Cobalt 
                 0-2.0% 
               
                   
                 Tungsten 
                 0-4.0% 
               
                   
                 Hafnium 
                 0.01-4.5%   
               
                   
                 Aluminum 
                 0-15%  
               
                   
                 Nitrogen 
                 0.001-0.5%    
               
                   
                 Oxygen 
                 0.001-0.7%    
               
                   
                   
               
           
              
             
             
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
             
          
         
       
       balance iron and incidental impurities. 
     
   
   
       5 . The method according to  claim 1 , wherein the hafnium oxide particles have a particle size of less than 50 microns. 
   
   
       6 . The method according to  claim 1 , wherein the hafnium oxide particles have a particle size ranging from 5 microns to 0.25 microns or less. 
   
   
       7 . The method according to  claim 1 , in which the amount of hafnium added to the melt is from 0.01 to 3.0% by weight. 
   
   
       8 . The method according to  claim 1 , wherein the hafnium particles are added to the melt shortly before pouring the molten alloy into a mold. 
   
   
       9 . The method according to  claim 8 , in which the hafnium particles are added to the molten alloy in a ladle. 
   
   
       10 . The method according to  claim 8 , in which the hafnium particles are added to the molten alloy in the furnace. 
   
   
       11 . The method according to  claim 1 , in which the hafnium is electrolytic hafnium. 
   
   
       12 . The method according to  claim 1 , wherein adding finely divided hafnium particles to the melt of the alloy before pouring comprises adding finely divided hafnium particles to the melt of the alloy before pouring, under conditions such that formation of detrimental oxide from reactive elements titanium, zirconium or aluminum is reduced. 
   
   
       13 . The method according to  claim 12 , wherein any one of the reactive elements titanium, zirconium or aluminum are added to the melt after the addition of hafnium into the melt. 
   
   
       14 . The method according to  claim 13 , wherein any one of the reactive elements titanium, zirconium or aluminum are added to the melt after the addition of hafnium in the melt, and just before pouring into the mold. 
   
   
       15 . The method according to  claim 14 , wherein the titanium is added to the melt in a form of TiFe after said hafnium addition. 
   
   
       16 . The method according to  claim 1 , wherein oxygen in the melt is varied by an addition of one or more substance selected from the group consisting of: silicon, chromium, manganese, calcium, CaSi, CaSiMn, niobium, titanium and zirconium. 
   
   
       17 . The method according to  claim 1 , further comprising adding finely divided hafnium particles to the melt of the alloy and varying the level of oxygen in the melt by adding at least one substance selected from the group consisting of: silicon, chromium, manganese, calcium, CaSi, CaSiMn, niobium, titanium and zirconium. 
   
   
       18 . The method according to  claim 1 , wherein adding finely divided hafnium particles to the melt of the alloy further comprises adding finely divided hafnium particles to the melt of the alloy, the addition of the hafnium particles controlling at least one of:
 (a) the partial pressure of oxygen to permit the oxidation of the hafnium particles in situ;   (b) the free oxygen content to permit the oxidation of the hafnium particles in situ; and   (c) the partial pressure of at least one element selected from the group consisting of: oxygen, carbon, nitrogen and hydrogen to permit the oxidation of the hafnium particles in situ.   
   
   
       19 . The method according to  claim 1  wherein the nickel-chromium-iron alloy is melted at a temperature in the range of from 1350° C. to 1700° C. 
   
   
       20 . The method according to  claim 1 , wherein the nickel-chromium-iron alloy is formed into a tube by rotational molding. 
   
   
       21 . A method for manufacturing an oxide dispersion strengthened nickel-chromium-iron alloy which comprises adding finely divided hafnium particles to a melt of the alloy permitting oxidation in situ of beneficial oxide dispersion as hafnium oxide, avoiding forming detrimental precipitates. 
   
   
       22 . The method according to  claim 21 , wherein adding finely divided hafnium particles to the melt of the alloy permitting oxidation in situ of beneficial oxide dispersion as hafnium oxide further comprises limiting the in situ oxidation to beneficial oxide dispersion of hafnium oxide and avoids the oxide dispersion of hafnium oxides reaction with slag. 
   
   
       23 . A method for manufacturing a corrosion resistant nickel-chromium-iron alloy which comprises adding sequentially finely divided hafnium particles and aluminum to a melt of the alloy before pouring the melt of the alloy. 
   
   
       24 . The method according to  claim 23 , wherein the aluminum is added to the melt immediately before pouring the molten alloy into a mold. 
   
   
       25 . A method for manufacturing an oxide dispersion strengthened nickel-chromium-iron alloy, the alloy comprising by weight percent: 35% Nickel, 25% Chromium, 0.4% Carbon, 0.8-0.9% Niobium, 1.6-1.8% Silicon, 1.1-1.3% Manganese and the balance Iron, the method comprises:
 (a) melting the alloy in a furnace;   (b) heating the melted alloy to a tap temperature ranging from 1610° C. to 1670° C.;   (c) removing slag from the furnace; and   (d) removing the melted alloy from the furnace and adding hafnium particles having a particle size maximum of 5 mm to the melted alloy thereby transforming at least a part of the hafnium particles to hafnium oxide in the melted alloy thereby forming an oxide dispersion strengthened nickel-chromium-iron alloy.   
   
   
       26 . The method according to  claim 25 , wherein removing the melted alloy from the furnace and adding hafnium particles having a particle size maximum of 5 mm to the melted alloy comprises removing the melted alloy into a ladle and adding the hafnium particles to a tap stream during removal of the melted alloy from the furnace. 
   
   
       27 . The method according to  claim 25 , wherein the total amount of hafnium particles added to the melted alloy is 0.3 to 0.5% by weight of the melted alloy. 
   
   
       28 . The method according to  claim 25 , further comprising adding TiFe to the melted alloy after addition of the hafnium particles sufficient to provide a final amount of 0.18% by weight of titanium. 
   
   
       29 . A method for manufacturing a low-carbon oxide dispersion strengthened nickel-chromium-iron alloy, the alloy comprising by weight percent: 33%-35% Nickel, 24-26% Chromium, 0.04-08% Carbon, 1.0-1.2% Silicon, 1.0-1.2% Manganese, 0.14-0.3% Molybdenum and the balance Iron, the method comprises:
 (a) melting the alloy in a furnace;   (b) heating the melted alloy to a tap temperature ranging from 1610° C. to 1670° C.;   (c) removing slag from the furnace;   (d) removing the melted alloy from the furnace; and   (e) adding 0.5-0.75% hafnium particles by total weight of the alloy to the melted alloy, the hafnium particles having a particle size maximum of 5 mm transforming the hafnium to hafnium oxide in the melted alloy thereby forming an oxide dispersion strengthened nickel-chromium-iron alloy.   
   
   
       30 . The method according to  claim 29 , further comprising adding TiFe to the melted alloy after addition of the hafnium particles sufficient to provide a final amount of 0.25% by weight of titanium. 
   
   
       31 . A method for manufacturing an oxide dispersion strengthened nickel-chromium-iron alloy, the alloy comprising by weight percent: 35% Nickel, 25% Chromium, 0.4% Carbon, 0.8-0.9% Niobium, 1.6-1.8% Silicon, 1.1-1.3% Manganese and the balance Iron, the method comprises:
 (a) melting the alloy in a furnace;   (b) heating the melted alloy to a tap temperature ranging from 1630° C. to 1690° C.;   (c) removing slag from the furnace;   (d) removing the melted alloy from the furnace;   (e) adding 0.15-0.30% hafnium particles by total weight to the melted alloy, the hafnium particles having a particle size maximum of 5 mm, transforming the hafnium to hafnium oxide in the melted alloy; and   (f) adding 1.5% to 1.8% by weight aluminum to the melted alloy thereby forming an oxide dispersion strengthened nickel-chromium-iron alloy.