Sintered metal parts and method for the manufacturing thereof

Abstract

The invention relates to a method consisting of the steps of providing a pre-alloyed iron-based metal powder comprising at least 1.3-3.5% chromium, 0.15-0.7% molybdenum, manganese and unavoidable impurities, mixing said powder with 0.1-1.0% graphite, compacting the obtained mixture at a pressure of at least 600 MPa, sintering the compacted part in a single step at a temperature above 1100° C., shot-peening the part and after sintering optionally hardening the component. The invention also relates to a powder metallurgical part and use of a low chromium prealloyed powder for preparing notched sintered parts having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g/cm 3 , preferably at least 400 MPa at a sintered density of 7.3 g/cm 3 .

1 . A method for producing powder metallurgical parts with improved fatigue strength comprising the steps of: 
 providing a pre-alloyed iron-based metal powder comprising at least 1.3-3.5% by weight of chromium, 0.15-0.7% by weight of molybdenum,    mixing said powder with 0.1-1.0% by weight of graphite,    compacting the obtained mixture at a pressure of at least 600 MPa,    sintering the compacted part in a single step at a temperature above 1100° C., and    shot-peening the part.    
     
     
         2 . A method according to  claim 1  wherein the increase of the fatigue strength is at least 50%.  
     
     
         3 . The method according to  claim 1 , wherein the compacted and sintered part is subjected to hardening and tempering prior to shot peening.  
     
     
         4 . A powder metallurgical part manufactured according to  claim 1  having a mainly pearlitic microstructure.  
     
     
         5 . A powder metallurgical part manufactured according to  claim 1  having a martensitic and lower bainitic microstructure.  
     
     
         6 . The powder metallurgical part manufactured according to  claim 1  having a mainly tempered martensitic microstructure.  
     
     
         7 . The powder metallurgical part according to  claim 1  having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g/cm 3 .  
     
     
         8 . A method for preparing notched sintered parts having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g/cm 3 , comprising compacting a low chromium Prealloyed Powder to form a compacted part, sintering and optionally tempering and annealing said compacted part, and thereafter subjecting said compacted part to shot peening.  
     
     
         9 . A method for preparing notched sintered parts according to  claim 8 , wherein said parts have a stress concentration factor above 1.3.  
     
     
         10 . The method according to  claim 2 , wherein the compacted and sintered part is subjected to hardening and tempering prior to shot peening.  
     
     
         11 . A powder metallurgical part manufactured according to  claim 2  having a mainly pearlitic microstructure preferably mainly pearlitic microstructure.  
     
     
         12 . A powder metallurgical part manufactured according to  claim 3  having a mainly pearlitic microstructure preferably mainly pearlitic microstructure.  
     
     
         13 . A powder metallurgical part manufactured according to  claim 1  having a mainly fine pearlitic microstructure.  
     
     
         14 . A powder metallurgical part manufactured according to  claim 2  having a martensitic and lower bainitic microstructure.  
     
     
         15 . A powder metallurgical part manufactured according to  claim 3  having a martensitic and lower bainitic microstructure.  
     
     
         16 . The powder metallurgical part manufactured according to  claim 2  having a mainly tempered martensitic microstructure.  
     
     
         17 . The powder metallurgical part manufactured according to  claim 3  having a mainly tempered martensitic microstructure.  
     
     
         18 . A powder metallurgical part according to  claim 1  having a bending fatigue limit of at least 400 MPa at a sintered density of 7.3 g/cm 3 .  
     
     
         19 . The powder metallurgical part according to  claim 2  having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g/cm 3 .  
     
     
         20 . A method for preparing notched sintered parts according to  claim 8  wherein said parts have a bending fatigue limit of at least 400 MPa at a sintered density of 7.3 g/cm 3 .