Method of producing powder metal parts

Abstract

A method of producing parts from powdered metal comprising the steps of providing a metallurgic powder comprising iron, 0-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, 0-0.5 weight percent manganese, and 0-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder. Next, the metallurgic powder is compressed 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 high temperature sintered at a temperature of 2100° F. to 2400° F. 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.

What is claimed is:  
     
         1 . A method of producing parts from powdered metal comprising the steps of: 
 a) providing a metallurgic powder comprising iron, 0-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, 0-0.5 weight percent manganese, and 0-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder;    b) compressing the metallurgic powder at a pressure of 25 to 65 tsi to provide a green compact;    c) heating the compact to 2100° F. to 2400° F. for 20 to 60 minutes;    d) holding the compact between 1000° F. to 1900° F. for 5 to 60 minutes, 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) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes;    g) cooling the compact at a rate of 150° F. to 250° F. per minute; and    h) 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 has a hardness of 27 to 50 HRC.    
     
     
         2 . The method of  claim 1 , wherein the parts are sprockets.  
     
     
         3 . The method of  claim 2 , wherein the sprockets have a tooth density of 6.75 g/cc to 7.25 g/cc.  
     
     
         4 . The method of  claim 1 , wherein the step of compressing the metallurgic powder produces a compact with a density of 6.4 g/cc to 7.4 g/cc.  
     
     
         5 . The method of  claim 1 , wherein the compact is heated in step c) to a temperature of 2300° F. for 40 minutes.  
     
     
         6 . The method of  claim 1 , wherein the compact is held in step d) at a temperature between 1000° F. to 1800° F.  
     
     
         7 . The method of  claim 1 , wherein the compact is held in step d) at a temperature between 1500° F. to 1900° F.  
     
     
         8 . The method of  claim 1 , wherein the compact is not subjected to additional cooling or heating between steps c) and d).  
     
     
         9 . The method of  claim 8 , wherein the compact produced in step c) has a critical temperature and in step d) is held below the critical temperature.  
     
     
         10 . The method of  claim 8 , wherein the compact produced in step c) has a critical temperature and in step d) is held at the critical temperature.  
     
     
         11 . The method of  claim 1 , wherein the Pearlite may be spheroidized.  
     
     
         12 . A method of producing parts from powdered metal comprising the steps of: 
 a) providing a metallurgic powder comprising iron, 0-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, 0-0.5 weight percent manganese, and 0-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder;    b) compressing the metallurgic powder at a pressure of 25 to 65 tsi to provide a compact with a density of 6.4 to 7.4 g/cc;    c) heating the compact to 2100° F. to 2400° F. for 20 to 60 minutes and cooling the compact to room temperature;    d) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes;    e) cooling the compact at a rate of 150° F. to 250° F. per minute; and    f) heating the compact to 300° F. to 1000° F. for 30 to 90 minutes.    
     
     
         13 . The method of  claim 12 , wherein the compact is heated in step c) is to a temperature of 2300° F. for 40 minutes.  
     
     
         14 . A method of producing parts from powdered metal comprising the steps of: 
 a) providing a metallurgic powder comprising iron, 0-1.5 weight percent silicon, 0.4-0.9 weight percent carbon, 0.5-4.5 weight percent nickel, 0.5-1.0 weight percent molybdenum, 0-0.5 weight percent manganese, and 0-1.5 weight percent copper, the weight percentages calculated based on the total weight of the powder;    b) compressing the metallurgic powder at a pressure of 25 to 65 tsi to provide a compact with a density if 6.4 to 7.4 g/cc;    c) heating the compact to 1650° F. to 2100° F. for 20 to 80 minutes;    d) cooling the compact at a rate of 150° F. to 250° F. per minute; and    e) heating the compact to 300° F. to 1000° F. for 30 to 90 minutes.