Method for Treating Elongated Metal Product by Heating and Oxidizing the Surface in a Controlled Environment

Abstract

A method and apparatus are provided for making a metal product with improved surface characteristics. The method provides for treating the metal product through a method including: heating the metal product; exposing the outer surface of the metal product to a controlled environment; and oxidising the outer surface of the metal product. The heating may take the metal product to an elevated temperature, the elevated temperature of the metal product being at least 725° C. The method further includes a controlled environment around the metal product which is controlled with respect to the atmosphere around the metal product, and in particular the nitrogen and/or oxygen and/or hydrogen content thereof. The result is a more consistent surface for elongate metal products, having a more consistent colour to the surface, a more durable and hard wearing surface and/or a surface which is not prone to flaking.

1 . A method for treating a metal product, the method comprising:
 heating the metal product;   exposing the outer surface of the metal product to a controlled environment; and   oxidising the outer surface of the metal product.   
     
     
         2 . The method according to  claim 1 , the method further comprising heating the metal product to an elevated temperature, the elevated temperature of the metal product being at least 725° C. 
     
     
         3 . The method according to  claim 1 , the method further comprising the controlled environment being controlled with respect to the atmosphere around the metal product. 
     
     
         4 . The method according to  claim 3 , the method further comprising the nitrogen and/or oxygen and/or hydrogen content being controlled. 
     
     
         5 . The method according to  claim 1 , the method further comprising the controlled environment being provided within a container provided in a first process stage, the container being a tube or other elongate container, and the metal product passing through the container. 
     
     
         6 . The method according to  claim 1 , in which a gas mixture is fed to the controlled environment and in which the H 2  to O 2  ratio in the total gas mixture is between 1.5:1 and 4:1. 
     
     
         7 . The method according to  claim 1 , in which a gas mixture is fed to the controlled environment and in which the H 2  to O 2  ratio in the total gas mixture is between 1.65:1 and 3.5:1. 
     
     
         8 . The method according to  claim 1 , in which a gas mixture is fed to the controlled environment and in which the H 2  to O 2  ratio in the total gas mixture is between 1.5:1 and 2:1 
     
     
         9 . The method according to  claim 1 , in which a gas mixture is fed to the controlled environment and in which the H 2  to O 2  ratio in the total gas mixture is between 3.2:1 and 3.7:1. 
     
     
         10 . The method according to  claim 1 , the method further comprising that the surface of the metal product oxidises in a first process stage. 
     
     
         11 . The method according to  claim 10 , in which the oxidation is substantially completed in the controlled environment. 
     
     
         12 . The method according to  claim 1 , the method further comprising that the surface of the metal product is reduced in a first process stage. 
     
     
         13 . The method according to  claim 12 , in which the reduction is substantially completed in the controlled environment. 
     
     
         14 . The method according to  claim 1 , in which the method further comprises a quenching stage, the quenching stage being provided after the first process stage, the quench stage hardening the metal product. 
     
     
         15 . The method according to  claim 1 , in which the method further comprises a further immersion stage, the further immersion stage being provided after the first process stage and/or after the quenching stage, the further immersion stage tempering the metal product. 
     
     
         16 . The method according to  claim 1 , in which the method further comprises a further quenching stage, the further quenching stage being provided after the first process stage and/or after the quenching stage and/or after the further immersion stage, the further quenching stage hardening the metal product. 
     
     
         17 . The method according to  claim 1 , in which the method of treating provides that the characteristics and/or properties of the surface do not alter after the quenching stage, particularly with respect to the oxidisation of the surface. 
     
     
         18 . The method according to  claim 17  in which the method provides that less than 1% of the oxidation of the surface of the metal product occurs after the further quenching stage, preferably after the tempering stage and most preferably after the quenching stage. 
     
     
         19 . Apparatus for treating a metal product, the apparatus comprising:
 a heating stage for heating the metal product;   a controlled environment, to which the outer surface of the metal product is exposed;   an oxidising stage for oxidising the outer surface of the metal product.   
     
     
         20 . A method for treating a metal product, the method comprising:
 heating the metal product;   exposing the outer surface of the metal product to a controlled environment;   oxidising the outer surface of the metal product;   quenching the metal product; and   tempering the metal product.   
     
     
         21 . Apparatus for treating a metal product, the apparatus comprising:
 a heating stage for heating the metal product;   a controlled environment, to which the outer surface of the metal product is exposed;   an oxidising stage for oxidising the outer surface of the metal product;   a quenching stage for quenching the metal product; and   an tempering stage for tempering the metal product.