Method for manufacturing a Ni-based alloy article and product therefrom

Abstract

A method for manufacturing a Ni-based alloy article which elutes little Ni even when used in a high-temperature water environment for a long period comprises heating the Ni-based alloy in a carbon dioxide-containing atmosphere for a set period of time at an elevated temperature to form an oxide film comprising chromium oxide on a surface thereof. Using carbon dioxide as an oxidizing gas produces an oxide film of generally uniform thickness along a length of the article being treated so that resistance to nickel elution is more uniform over the entire article.

1 . In a method of forming an oxide film comprising chromium oxide on a surface of a nickel based chromium containing alloy article by subjecting the alloy to an oxidizing treatment at an elevated temperature for a period of time, the oxidizing treatment including the use of an oxidizing gas, the improvement comprising providing an effective amount of carbon dioxide as the oxidizing gas to form the oxide film, the oxide film having a generally uniform thickness along a length of the alloy article being treated.  
   
   
       2 . The method of  claim 1 , wherein oxidizing gas comprises a mixture of one or more of hydrogen, oxygen and an inert gas, with the effective amount of carbon dioxide gas.  
   
   
       3 . The method of  claim 2 , wherein the oxidizing gas comprises a mixture of hydrogen and carbon dioxide.  
   
   
       4 . The method of  claim 2 , wherein a concentration of the oxidizing gas ranges between 0.0001% and 99.9999% by volume of carbon dioxide with the balance being one or more of hydrogen, oxygen and the inert gas.  
   
   
       5 . The method of  claim 4 , wherein the concentration of the carbon dioxide is between 0.0001% and 1.0% by volume.  
   
   
       6 . The method of  claim 5 , wherein a remainder of the oxidizing gas is hydrogen.  
   
   
       7 . The method of  claim 1 , wherein the elevated temperature ranges between 500° and 1,250° C.  
   
   
       8 . The method of  claim 1 , wherein the period of time ranges between 10 seconds and 35 hours.  
   
   
       9 . The method of  claim 1 , wherein the nickel-based chromium containing alloy comprises, by mass %: 0.15% or less C; 1.00% or less Si; 2.0% or less Mn; 0.030% or less P; 0.030% or less S; 10.0-40.0% Cr; 15.0% or less Fe; 0.5% or less Ti; 0.50% or less Cu; 2.00% or less Al; and the balance Ni with unavoidable impurities.  
   
   
       10 . The method of  claim 1 , wherein the alloy article is a tube, the surface is an inner surface of the tube, and the oxidizing gas is introduced into one end of the tube and removed from an opposite end.  
   
   
       11 . The method of  claim 10 , wherein the alloy article tube has a thickness of the oxide film t in  as measured at the opposite end, and a thickness of oxide film t out  as measured at the one end, and |t in -t out |/t in <1.0.  
   
   
       12 . The method of  claim 1 , wherein the alloy article is made of a nickel-based chromium containing alloy suitable for a member for a nuclear power plant.  
   
   
       13 . The method of  claim 12 , wherein the member for nuclear power plant is a steam generator tube.  
   
   
       14 . A nickel-based chromium containing alloy tube of set length and having an inner surface coated with an oxide film comprising chromium oxide, wherein one end of the tube has an oxide film thickness of t in  and an opposite end of the tube has an oxide film thickness of t out , and wherein the oxide film thicknesses satisfy the equation |t in -t out |/t in <1.0.  
   
   
       15 . The alloy tube of  claim 14 , wherein the alloy tube is made of a nickel-based chromium containing alloy suitable for use as a tube for a nuclear power plant.  
   
   
       16 . The alloy tube of  claim 15 , wherein the tube for a nuclear power plant is a steam generator tube.  
   
   
       17 . The alloy tube of  claim 14 , wherein the nickel-based chromium containing alloy comprises, by mass %: 0.15% or less C; 1.00% or less Si; 2.0% or less Mn; 0.030% or less P; 0.030% or less S; 10.0-40.0% Cr; 15.0% or less Fe; 0.5% or less Ti; 0.50% or less Cu; 2.00% or less Al; and the balance Ni with unavoidable impurities.