Method of producing powder metal parts

Abstract

A method of producing parts from powdered metal comprising the steps of providing a metallurgic powder, compressing the powder at a pressure of 25 to 65 tsi to provide a green compact with a density if 6.4 g/cc to 7.4 g/cc. The compact is then high temperature sintered at a temperature of 2100° F. to 2400° F. for 20 to 60 minutes or regularly sintered at a temperature of 1650° F. to 2400° F. for 20 to 80 minutes, held between 1000° F. to 1800° F. for 5 to 60 minutes, and then cooled to room temperature. Then, the compact is selectively densified to greater than 7.6 g/cc. The compact is sinter hardened to obtain a mainly Martensite microstructure. The compact can be directly high temperature sinter hardened if selective densification is not necessary. Material made by this method is also disclosed.

1 . A method of producing a part from a metallurgic powder comprising the steps of: 
 a) compressing the metallurgic powder at a pressure of 25 to 65 tsi to form a compact;    b) heating the compact to 1650° F. to 2400° F. for 20 to 60 minutes;    c) holding the compact between 1000° F. to 1900° F. for 5 to 60 minutes;    d) cooling the compact to room temperature, such that microstructure of the compact becomes mainly pearlite;    e) increasing the density of at least a portion of the compact to greater than 7.6 g/cc;    f) sinter hardening the compact by the steps of: 
 i) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes;  
 ii) cooling the compact at a rate of 150° F. to 250° F. per minute to room temperature;  
   g) tempering the compact by heating the compact to 300° F. to 1000° F. for 30 to 90 minutes, such that the microstructure of the compact becomes tempered martensite, 0% to 20% bainite, and less than 5% retained austenite and the compact has a hardness of 27 to 65 HRC.    
     
     
         2 . The method of  claim 1 , wherein the metallurgic powder is comprised of iron, 0.1-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         3 . The method of  claim 1 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.5-1.0 weight percent molybdenum, and 0.1-4.0 weight percent chromium, the weight percentages calculated based on the total weight of the powder.  
     
     
         4 . The method of  claim 3 , wherein the metallurgic powder further comprises up to 0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         5 . The method of  claim 3 , wherein the metallurgic powder further comprises up to 1.5 weight percent silicon, the weight percentages calculated based on the total weight of the powder.  
     
     
         6 . The method of  claim 3 , wherein the metallurgic powder further comprises up to 4.5 weight percent nickel, the weight percentages calculated based on the total weight of the powder.  
     
     
         7 . The method of  claim 3 , wherein the metallurgic powder further comprises up to 2.0 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         8 . The method of  claim 1 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.1-1.5 weight percent molybdenum, and 0.1-2.0 weight percent nickel, 0.1-0.5 weight percent manganese, and 0.1-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         9 . The method of  claim 1 , wherein the part is a sprocket.  
     
     
         10 . The method of  claim 9 , wherein the sprocket has a tooth density of 6.75 g/cc to 7.25 g/cc after step g).  
     
     
         11 . The method of  claim 1 , wherein after step a) of compressing the metallurgic powder, the compact has a density of 6.4 g/cc to 7.4 g/cc.  
     
     
         12 . The method of  claim 1 , wherein the compact is heated in step b) to a temperature of 2300° F. for 30 minutes.  
     
     
         13 . The method of  claim 1 , wherein the compact is heated in step b) to a temperature of 2070° F. for 30 minutes.  
     
     
         14 . The method of  claim 1 , wherein the compact is not cooled below the holding temperature of step c) between steps b) and c).  
     
     
         15 . The method of  claim 14 , wherein step b) produces a compact having a critical temperature of 1510° F. and in step c) the compact is held below the critical temperature at a temperature of 1450° F. for 15 minutes.  
     
     
         16 . The method of  claim 14 , wherein the compact produced in step c) has a critical temperature of 1510° F. and in step d) is held at the critical temperature of 1510° F. for 15 minutes.  
     
     
         17 . A method of producing a part from a metallurgic powder comprising the steps of: 
 a) compressing the metallurgic powder at a pressure of 25 to 65 tsi to form a compact;    b) heating the compact to 2100° F. to 2400° F. for 20 to 60 minutes;    c) sinter hardening the compact by the steps of: 
 i) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes; and  
 ii) cooling at a rate of 150° F. to 250° F. per minute to room temperature;  
   d) tempering the compact by heating the compact to 300° F. to 1000° F. for 20 to 90 minutes.    
     
     
         18 . The method of  claim 17 , wherein the metallurgic powder is comprised of iron, 0.1-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         19 . The method of  claim 17 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.1-2.0 weight percent nickel, 0.1-1.5 weight percent molybdenum, 0.1-0.5 weight percent manganese, and 0.1-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         20 . The method of  claim 17 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-4.0 weight percent chromium, the weight percentages calculated based on the total weight of the powder.  
     
     
         21 . The method of  claim 20 , wherein the metallurgic powder further comprises up to 0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         22 . The method of  claim 20 , wherein the metallurgic powder further comprises up to 1.5 weight percent silicon, the weight percentages calculated based on the total weight of the powder.  
     
     
         23 . The method of  claim 20 , wherein the metallurgic powder further comprises up to 4.5 weight percent nickel, the weight percentages calculated based on the total weight of the powder.  
     
     
         24 . The method of  claim 20 , wherein the metallurgic powder further comprises up to 2.0 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         25 . A method of producing a part from a metallurgic powder comprising the steps of: 
 a) compressing the metallurgic powder at a pressure of 25 to 65 tsi to form a compact;    b) heating the compact to 2100° F. to 2400° F. for 20 to 60 minutes; and    c) cooling the compact to room temperature at a rate of 150° F. to 250° F. per minute;    d) tempering the compact by heating the compact to 300° F. to 1000° F. for 20 to 90 minutes.    
     
     
         26 . The method of  claim 25 , wherein the metallurgic powder is comprised of iron, 0.1-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         27 . The method of  claim 25 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.1-2.0 weight percent nickel, 0.1-1.5 weight percent molybdenum, 0.1-0.5 weight percent manganese, and 0.1-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         28 . The method of  claim 25 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-4.0 weight percent chromium, the weight percentages calculated based on the total weight of the powder.  
     
     
         29 . The method of  claim 28 , wherein the metallurgic powder further comprises up to 0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         30 . The method of  claim 28 , wherein the metallurgic powder further comprises up to 1.5 weight percent silicon, the weight percentages calculated based on the total weight of the powder.  
     
     
         31 . The method of  claim 28 , wherein the metallurgic powder further comprises up to 4.5 weight percent nickel, the weight percentages calculated based on the total weight of the powder.  
     
     
         32 . The method of  claim 28 , wherein the metallurgic powder further comprises up to 2.0 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         33 . A method of producing a part from a metallurgic powder comprising the steps of: 
 a) compressing the metallurgic powder at a pressure of 25 to 65 tsi to form a compact;    b) sinter hardening the compact by the steps of: 
 i) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes; and  
 ii) cooling at a rate of 150° F. to 250° F. per minute to room temperature;  
   c) tempering the compact by heating the compact to 300° F. to 1000° F. for 20 to 90 minutes.    
     
     
         34 . The method of  claim 33 , wherein the metallurgic powder is comprised of iron, 0.1-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         35 . The method of  claim 33 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.1-2.0 weight percent nickel, 0.1-1.5 weight percent molybdenum, 0.1-0.5 weight percent manganese, and 0.1-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder.  
     
     
         36 . The method of  claim 33 , wherein the metallurgic powder is comprised of iron, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, and 0.1-4.0 weight percent chromium, the weight percentages calculated based on the total weight of the powder.  
     
     
         37 . The method of  claim 36 , wherein the metallurgic powder further comprises up to 0.5 weight percent manganese, the weight percentages calculated based on the total weight of the powder.  
     
     
         38 . The method of  claim 36 , wherein the metallurgic powder further comprises up to 1.5 weight percent silicon, the weight percentages calculated based on the total weight of the powder.  
     
     
         39 . The method of  claim 36 , wherein the metallurgic powder further comprises up to 4.5 weight percent nickel, the weight percentages calculated based on the total weight of the powder.  
     
     
         40 . The method of  claim 36 , wherein the metallurgic powder further comprises up to 2.0 weight percent copper, the weight percentages calculated based on the total weight of the powder.