Method of forming powder metal components having surface densification

Abstract

A method for producing a powder metal article having a three dimensional shape and having at least one densified surface comprising: a) providing a blend of powdered metals; b) compacting said blend to form a pre-form having a general shape of said article; c) sintering said pre-form; d) densifying at least one cylindrical surface region of said pre-form; and, e) forming said pre-form to a final density and into the three dimensional shape of said article.

1 . A method for producing a powder metal article having a three dimensional shape and having at least one densified surface region, said method comprising:
 a) providing a blend of powdered metals;   b) compacting the blend to form a pre-form having a general shape of the article, said preform being generally cylindrically shaped at a region corresponding to said at least one densified surface region;   c) sintering said pre-form;   d) densifying said at least one surface region of said pre-form; and,   e) forming said pre-form to a desired final density and into a desired three dimensional shape of said article.   
   
   
       2 . The method of  claim 1  wherein said step of densifying comprises cold rolling said at least one surface. 
   
   
       3 . The method of  claim 1  further comprising:
 f) subjecting said article to annealing.   
   
   
       4 . The method of  claim 1  further comprising:
 f) subjecting said article to heat treatment.   
   
   
       5 . The method of  claim 1  wherein said powder is compacted in step (b) to a density of between 70% and 90% of the theoretical maximum density. 
   
   
       6 . The method of  claim 1  wherein step (d) comprises densifying said at least one surface region to a density of at least 80% of the theoretical maximum density. 
   
   
       7 . The method of  claim 1  wherein step (d) comprises densifying said at least one surface region to a density of between 95% and 100% of the theoretical maximum density. 
   
   
       8 . The method of  claim 1  wherein said forming step includes compressing said pre-form to a core density of at least 90% of the theoretical maximum density. 
   
   
       9 . The method of  claim 1  wherein said forming step includes compressing said pre-form to a core density of between 90% and 98% of the theoretical maximum density. 
   
   
       10 . The method of  claim 1  wherein said at least one surface region has a thickness of between 0.001 and 0.04 inches after densification. 
   
   
       11 . The method of  claim 1  wherein said powder metal blend comprises compressible iron powder, at least one ferro alloy, a lubricant, and carbon in the form of graphite. 
   
   
       12 . The method  claim 11  wherein said ferro alloy comprises an alloy of iron with a metal chosen from the group consisting of: chromium, copper, manganese, molybdenum, nickel, niobium, vanadium, and combinations thereof. 
   
   
       13 . The method of  claim 12  wherein said ferro alloy is chosen from the group consisting of: ferro manganese, ferro molybdenum, and ferro chromium. 
   
   
       14 . The method of  claim 1  wherein said powder blend comprises: elemental or substantially pure powder blends; fully pre-alloyed powder blends; partially pre-alloyed powder blends; or, powder blends containing ferro alloys. 
   
   
       15 . The method of  claim 1  further including an isothermal treatment step following said sintering step (c). 
   
   
       16 . The method of  claim 1  further including an isothermal treatment step, wherein said isothermal treatment is included in a cooling phase of said sintering step (c). 
   
   
       17 . A method for producing a powder metal article having a three dimensional shape and having at least one densified surface region, said method comprising:
 a) providing a blend of powdered metals;   b) compacting the blend to form a pre-form having a general shape of the article, said pre-form having a density of between 70% to 90% of the theoretical maximum density and being generally cylindrically shaped at a region corresponding to said at least one densified surface region;   c) sintering said pre-form;   d) densifying said at least one surface region of said pre-form to at least 80% of the theoretical maximum density; and,   e) forming said pre-form to a desired final density and into a desired three dimensional shape of said article.   
   
   
       18 . The method of  claim 17  further including an isothermal treatment step following said sintering step (c). 
   
   
       19 . The method of  claim 17  further including an isothermal treatment step, wherein said isothermal treatment is included in a cooling phase of said sintering step (c). 
   
   
       20 . A powder metal pre-form having a general shape of a desired article, said pre-form having a density of between 70% to 90% of the theoretical maximum density and being generally cylindrically shaped at least one surface region. 
   
   
       21 . A powder metal article formed from the pre-form of  claim 20 .