Method of producing powder metal parts using induction sintering

Abstract

A method of forming a part from a metallurgical powder includes compressing a metallurgical powder including no more than 0.3 weight percent of lubricant within a die to provide a green compact. The green compact is subsequently sintered by induction heating up to a sintering temperature of the green compact and maintaining the compact at the temperature for a time sufficient to provide a sintered compact. The sintered part may be subsequently hot formed and/or forged to densify and adjust the dimensions of the sintered compact.

What is claimed is:  
     
         1 . A method of forming a part from a metallurgical powder, the method comprising: 
 compressing a metallurgical powder comprising 0 up to 0.3 weight percent of internal lubricant within a die to provide a green compact; and    sintering the green compact by induction heating the green compact to provide a sintered compact.    
     
     
         2 . The method of  claim 1 , wherein the metallurgical powder further comprises a particulate metallic material that may be heated by induction.  
     
     
         3 . The method of  claim 2 , wherein the particulate metallic material is least one of a pure iron powder and an iron-containing powder.  
     
     
         4 . The method of  claim 2 , wherein the metallurgical powder is one of a single powder and a powder blend.  
     
     
         5 . The method of  claim 1 , wherein the metallurgical powder comprises 0 up to 3 weight percent graphite, 0 up to 12 weight percent nickel, 0 up to 3 weight percent molybdenum, 0 up to 10 weight percent copper, 0 up to 2 weight percent manganese, 0 up to 20 weight percent chromium, and iron.  
     
     
         6 . The method of  claim 1 , wherein the metallurgical powder comprises 0 up to 1 weight percent graphite, 0 up to 6 weight percent nickel, 0 up to 2 weight percent molybdenum, 0 up to 3 weight percent copper, 0 up to 1 weight percent manganese, 0 up to 3 weight percent chromium, and iron.  
     
     
         7 . The method of  claim 1 , wherein sintering the green compact comprises induction heating the green compact to a sintering temperature within the range of 1900° F. to 2500° F.  
     
     
         8 . The method of  claim 1 , wherein the metallurgical powder is free of internal lubricant.  
     
     
         9 . The method of  claim 1 , wherein the metallurgical powder comprises at least one internal lubricant selected from ethylene bis-stearamide, zinc stearate, and stearic acid.  
     
     
         10 . The method of  claim 1 , wherein compressing at least a portion of the metallurgical powder comprises compressing at least a portion of the metallurgical powder in at least one of a self-lubricating die and a die including a die wall coated with a material to reduce friction and die wear.  
     
     
         11 . The method of  claim 1 , wherein compressing the metallurgical powder comprises compressing the metallurgical powder at a pressure in the range of 10 up to 70 tsi.  
     
     
         12 . The method of  claim 5 , wherein the green compact has a green strength of at least 1000 psi.  
     
     
         13 . The method of  claim 5 , wherein the green compact has a density of at least 4.0 g/cc.  
     
     
         14 . The method of  claim 1 , wherein induction heating the green compact comprises inducing a current within the green compact to increase the temperature of the green compact to a sintering temperature of the green compact.  
     
     
         15 . The method of  claim 1 , wherein induction heating the green compact comprises placing the green compact within an induction work coil while passing alternating current through the coil to thereby induce a secondary current within the green compact through electromagnetic induction.  
     
     
         16 . The method of  claim 14 , wherein the green compact is maintained at the sintering temperature for a time in the range of 2 up to 600 seconds.  
     
     
         17 . The method of  claim 14 , wherein the green compact comprises 0 up to 3 weight percent graphite, 0 up to 12 weight percent nickel, 0 up to 3 weight percent molybdenum, 0 up to 10 weight percent copper, 0 up to 2 weight percent manganese, 0 up to 20 weight percent chromium, and balance iron and incidental impurities, and further wherein the green compact is maintained at the sintering temperature for at least 20 up to 180 seconds.  
     
     
         18 . The method of  claim 14 , wherein the sintering temperature, measured in Fahrenheit degrees, is 60 up to 95 percent of the melting point of the primary component of the metallurgical powder.  
     
     
         19 . The method of  claim 1 , further comprising: 
 processing the sintered compact by at least one of hot forming and forging the sintered compact.    
     
     
         20 . The method of  claim 19 , wherein hot forming and forging the sintered compact comprises placing the sintered compact in a heated die and applying pressure to the sintered compact.  
     
     
         21 . The method of  claim 20 , wherein the heated die is at a temperature in the range of 200 up to 800° F. (93° C. up to 427° C.).  
     
     
         22 . The method of  claim 20 , wherein 20 up to 90 tsi pressure is applied to the sintered compact.  
     
     
         23 . The method of  claim 20 , wherein about 40 tsi pressure is applied to the sintered compact.  
     
     
         24 . The method of  claim 20 , further comprising prior to hot forming the sintered compact, cooling the sintered compact to a temperature less than the sintering temperature.  
     
     
         25 . The method of  claim 24 , wherein cooling the sintered compact comprises cooling the sintered compact to a temperature in the range of 1400 up to 2100° F. (1371° C.).  
     
     
         26 . A method of forming a part from a metallurgical powder, the method comprising: 
 compressing a metallurgical powder comprising predominantly iron and further comprising 0 up to 3 weight percent graphite, 0 up to 12 weight percent nickel, 0 up to 3 weight percent molybdenum, 0 up to 10 weight percent copper, 0 up to 2 weight percent manganese, 0 up to 20 weight percent chromium, and up to 0.3 weight percent internal lubricant, within a die at a pressure in the range of 10 up to 70 tsi to provide a green compact;    sintering the green compact by induction heating the green compact to a sintering temperature of the green compact, and maintaining the sintering temperature for a time in the range of 2 up to 600 seconds to provide a sintered compact;    cooling the sintered compact to a temperature lower than the sintering temperature; and    processing the sintered compact by at least one of hot forming and forging the sintered compact by placing the sintered compact in a heated die and applying a pressure in the range of 20 up to 90 tsi to the sintered compact.    
     
     
         27 . The method of  claim 26 , wherein the green compact has a density of at least 4.0 g/cc.  
     
     
         28 . The method of any of claims  1  and  26 , wherein the part is selected from a gear, a sprocket, a spur pinion, a helical pinion, a cam lobe, a bushing, a bearing, and a bearing race.  
     
     
         29 . A part formed by a method comprising: 
 compressing a metallurgical powder comprising 0 up to 0.3 weight percent of internal lubricant within a die to provide a green compact; and    sintering the green compact by induction heating the green compact to provide a sintered compact.    
     
     
         30 . The part of  claim 29 , wherein the method further comprises: 
 processing the sintered compact by at least one of hot forming and forging the sintered compact.    
     
     
         31 . A part formed by a method comprising: 
 compressing a metallurgical powder comprising predominantly iron and further comprising 0 up to 3 weight percent graphite, 0 up to 12 weight percent nickel, 0 up to 3 weight percent molybdenum, 0 up to 10 weight percent copper, 0 up to 2 weight percent manganese, 0 up to 20 weight percent chromium, and up to 0.3 weight percent lubricant, within a die at a pressure in the range of 10 up to 70 tsi to provide a green compact;    sintering the green compact by induction heating the green compact to a sintering temperature of the green compact and maintaining the sintering temperature for a time in the range of 2 up to 600 seconds to provide a sintered compact;    cooling the sintered compact to a temperature lower than the sintering temperature; and    processing the sintered compact by at least one of hot forming and forging the sintered compact in a heated die by applying a pressure in the range of 20 up to 90 tsi to the sintered compact.    
     
     
         32 . The part of any of claims  29  and  31 , wherein the part is selected from a gear, a sprocket, a spur pinion, a helical pinion, a cam lobe, a bushing, a bearing, and a bearing race.