Formable sintered alloy with dispersed hard phase

Abstract

A method of forming an iron based sintered body which comprises in % by mass: 0.4 to 1.0% of C; 0.5 to 3.5% of Cr; 0.1 to 1.7% of Mo; 0.3 to 3.0% of Cu and microstructure of about 20-50% dispersed martensite in a matrix of fine pearlite is provided. The method utilizes a step of cooling a sintered article at a rate not exceeding 0.5˜C/sec. Ni and/or Mn may also be included in the method.

1 . A method of forming an iron based sintered body having a microstructure of about 20-50% dispersed martensite in a matrix of fine pearlite, the method comprising the steps of:
 providing a mixture comprising a composition in % by mass: 0.4 to 1.0% of C; 0.5 to 3.5% of Cr; 0.1 to 1.7% of Mo; 0.3 to 3.0% of Cu, the balance being primarily Fe and unavoidable impurities and lubricant;   placing the mixture in a first mold possessing the approximate shape of a finished product;   subjecting the mold to compaction pressures of between generally 35 and 65 tsi to produce a green body compact;   sintering the green body compact at a temperature of between 1120˜C and 1180˜C to form a sintered article;   cooling the sintered article at a rate not exceeding 0.5˜C/sec;   thermally stabilizing the sintered article;   placing the sintered article in a second mold possessing the desired shape of the finished product;   subjecting the second mold to pressures generally between 50 and 75 tsi.   
     
     
         2 . The method of  claim 1  wherein the step of sintering the green body compact is performed in an atmosphere comprising about 90% nitrogen and 10% hydrogen. 
     
     
         3 . The method of  claim 1  wherein the step of thermally stabilizing the sintered article comprises cold treatment and tempering. 
     
     
         4 . The method of  claim 1 , wherein the step of providing a mixture further includes in % by mass: 0.1 to 0.5 of Mn. 
     
     
         5 . The method of  claim 1 , wherein the step of providing a mixture further includes in % by mass: 0.1 to 6.0 of Ni. 
     
     
         6 . The method of  claim 1 , wherein the first mold is in the form of a gerotor gear. 
     
     
         7 . The method of  claim 1 , wherein the second mold is in the form of a gerotor gear generally at net shape. 
     
     
         8 . The method of  claim 1 , wherein the step of sintering the green body compact at a temperature of between 1120˜C and 1180˜C is performed for about 25 minutes. 
     
     
         9 . A method of forming an iron based sintered body having a microstructure of about 20-50% dispersed martensite in a matrix of fine pearlite, the method comprising the steps of:
 providing a mixture comprising a composition in % by mass: 0.4 to 1.0% of C; 0.5 to 3.5% of Cr; 0.1 to 1.7% of Mo; 0.3 to 3.0% of Cu, the balance being primarily Fe and unavoidable impurities and lubricant;   placing the mixture in a first mold possessing the approximate shape of a finished product;   subjecting the mold to compaction pressures of between generally 35 and 65 tsi to produce a green body compact;   sintering the green body compact at a temperature of between 1120˜C and 1180˜C in an atmosphere comprising about 90% nitrogen and 10% hydrogen for about 25 minutes to form a sintered article;   cooling the sintered article at a rate not exceeding 0.5˜C/sec;   thermally stabilizing the sintered article;   placing the sintered article in a second mold possessing the desired shape of the finished product;   subjecting the second mold to pressures generally between 50 and 75 tsi.   
     
     
         10 . The method of  claim 9  wherein the step of thermally stabilizing the sintered article comprises cold treatment and tempering. 
     
     
         11 . The method of  claim 9 , wherein the step of providing a mixture further includes in % by mass: 0.1 to 0.5 of Mn. 
     
     
         12 . The method of  claim 9 , wherein the step of providing a mixture further includes in % by mass: 0.1 to 6.0 of Ni. 
     
     
         13 . The method of  claim 9 , wherein the first mold is in the form of a gerotor gear. 
     
     
         14 . The method of  claim 9 , wherein the second mold is in the form of a gerotor gear generally at net shape.