Low temperature nitrocarburizing salt and method of use

Abstract

A composition for nitrocarburizing stainless steel parts and a method for producing a nitride or hard case on such parts using the composition, are provided. The composition includes alkali metal cyanate and alkali metal carbonate, wherein the cyanate ion is present in a weight percentage of greater than 45% and less than 55.2%. The composition is fused and maintained between about 750° F. and about 950° F. depending upon the type of stainless steel to be treated. The workpiece is immersed in the fused bath and left in until a satisfactory compound layer or case is formed. With austenitic stainless steel, the piece is immersed from about four hours to about six hours at temperatures between about 750° F. and about 950° F., preferably between 750° F. and 850° F. to maintain corrosion resistance. With 400 series stainless steel, increased corrosion resistance is achieved by immersion for between four and six hours at 950° F.

What is claimed is:  
     
         1 . A composition for treating stainless steel parts at temperatures between 750° F. and 950° F. comprising alkali metal cyanates and alkali carbonate and wherein said cyanate ion is present in a weight percentage of greater than 45% and less than 55.2%, and wherein the composition is molten and homogenous at temperatures between 750° F. and 950° F.  
     
     
         2 . The invention as defined in  claim 1  wherein said cyanate ion is present in a weight percentage of greater than 45% and less than 50%.  
     
     
         3 . The invention as defined in  claim 1  wherein said cyanate ion is present in weight percentage of about 48%.  
     
     
         4 . The invention as defined in  claim 1  wherein said alkali metal is selected from the group of sodium, potassium, and mixtures thereof.  
     
     
         5 . The invention as defined in  claim 1  wherein said alkali metal is a mixture of sodium and potassium.  
     
     
         6 . The invention as defined in  claim 5  wherein the ratio of potassium to sodium is about 3.9 to 1.0.  
     
     
         7 . A method for producing a nitride or a hard case on a stainless steel workpiece comprising the steps of: 
 providing a fused bath of alkali metal cyanate, and alkali metal carbonate, wherein said cyanate ion is present in a weight percentage of greater than 45% and less than 55.2%, maintained at a temperature of between 750° F. and 950° F., and immersing a stainless steel workpiece in said bath for a sufficient time to form a hard case thereon.    
     
     
         8 . The invention as defined in  claim 7  wherein said cyanate ion is present in a weight percentage of between 48% and 50%.  
     
     
         9 . The invention as defined in  claim 7  wherein said cyanate ion is present in a weight percentage of about 48%.  
     
     
         10 . The invention as defined in  claim 7  wherein said alkali metal is selected from the group of sodium, potassium, and mixtures thereof.  
     
     
         11 . The invention as defined in  claim 7  wherein said alkali metal is a mixture of sodium and potassium.  
     
     
         12 . The invention as defined in  claim 11  wherein the ratio of potassium to sodium is about 3.9 to 1.0.  
     
     
         13 . The invention as defined in  claim 7  wherein said workpiece is austenitic stainless steel.  
     
     
         14 . The invention as defined in  claim 7  wherein the workpiece is hardenable stainless steel and the temperature is about 950° F.