Surface modification of stainless steels

Abstract

A process involves the continuous surface treatment of stainless steel coils with aqueous suspensions of rare earth oxide nano or micro particles or aqueous rare earth nitrate solutions of nano or micro particles. The surface treatment can be applied by roll coating, spraying or other conventional application techniques. The treated material in coil form is then heated in an annealing box using an open coil process whereby a wire is placed between coil laps to promote uniform atmosphere exposure. The atmosphere can be reducing or oxidizing and the times can vary from 1 hr to 100 hr. The atmosphere can also be wet (high dew point) or dry (low dew point). The surface treatment promotes a more uniform color to the subsequently developed oxide formed during anneal-type heat treatment. It also improves corrosion resistance of the processed stainless steel material. Materials treated in this manner are suitable for a variety of applications in the building systems, automotive and appliance markets.

What is claimed is: 
     
         1 . A process for modifying the surface of stainless steel strip comprising: Subjecting a coil of stainless steel strip having two sides to an open coil anneal process at a temperature of about 1000° F. to about 1800° F. for about 1 hour to greater than 72 hours. 
     
     
         2 . The process of  claim 1  wherein, prior to subjecting the coil of stainless steel strip to an open coil anneal process, coating said stainless steel strip on at least one of the said sides with at least one of an aqueous suspension comprising a rare earth oxide or an aqueous solution comprising a rare earth nitrate. 
     
     
         3 . The process of  claim 2 , wherein the rare earth oxide comprises nanoparticles. 
     
     
         4 . The process of  claim 2 , wherein the rare earth oxide comprises microparticles. 
     
     
         5 . The process of  claim 1  or  2 , wherein the open coil anneal process is performed in a dry atmosphere with a dewpoint of less than about 0° F. 
     
     
         6 . The process of  claim 5 , wherein the dewpoint is less than about −40° F. 
     
     
         7 . The process of  claim 1  or  2 , wherein the open coil anneal process is performed in a wet atmosphere with a dewpoint of more than 60° F. 
     
     
         8 . The process of  claim 7 , wherein the open coil anneal process is performed in a wet atmosphere with a dewpoint of more than 80° F. 
     
     
         9 . The process of  claim 2 , wherein the coating leaves a residue of a rare earth oxide in the range of about 300 to about 3000 μg/m 2 . 
     
     
         10 . The process of  claim 9 , wherein the residue of the rare earth oxide is in the range of 500 to about 1000 μg/m 2 . 
     
     
         11 . The process of  claim 1 , wherein, prior to subjecting the stainless strip to an open coil anneal process, at least one side of said stainless steel strip treated so as to impart to said side a surface finish selected from the group consisting of 2B, 2D, #4 Polish, ESD, and Greystone finishes. 
     
     
         12 . The process of  claim 2 , wherein, prior to coating said stainless steel strip, at least one side of said stainless steel strip treated so as to impart to said side a surface finish selected from the group consisting of 2B, 2D, #4 Polish, ESD, and Greystone finishes.