Nitrided sintered steels

Abstract

The present invention concerns a method of producing sintered components, and sintered components by the method. The method provides a cost effective production of sintered steel parts with wear resistance properties comparable to those of components made from chilled cast iron.

1 . A method of producing sintered components by single press/single sintering comprising the steps of:
 a) providing pre-alloyed iron-based steel powder comprising less than 0.3% by weight of Mn and at least one of Cr in an amount between 0.2-3.5% by weight, Mo in an amount between 0.05-1.20% by weight and V in an amount between 0.05-0.4% by weight, and maximum 0.5% incidental impurities, the balance being iron,   b) mixing said pre-alloyed iron-based steel powder with lubricant and graphite, and optionally machining enhancing agent(s) and other conventional sintering additives,   c) subjecting the mixed composition of step b) to compaction at pressures of 400-2000 MPa, thereby providing a compact,   d) sintering said compact from step c) in a reducing atmosphere at a temperature between 1000-1400° C., thereby providing a sintered component,   e) nitriding said sintered component of step d) in a nitrogen containing atmosphere, at a temperature of 400-600° C., with a soaking time of less than 3 hours,   
     
     
         2 . A method according to  claim 1 , wherein the lubricant consists of composite lubricant particles comprising a core of 10-60% by weight of at least one primary fatty acid amide having more than 18 and not more than 24 carbon atoms and 40-90% by weight of at least one fatty acid bisamide, said lubricant particles also comprising nanoparticles of at least one metal oxide adhered on the core. 
     
     
         3 . A method according to  claim 1 , wherein the compact is not steam treated before nitriding in step e). 
     
     
         4 . A method according to  claim 1 , wherein in step c) the compact is compacted to a green density of at least 7.10 g/cm 3 . 
     
     
         5 . A method according to  claim 1 , wherein in step d) the sintered component is sintered to a density between 7.1-7.6 g/cm 3 . 
     
     
         6 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder further comprises between 0.1-1.0% by weight of Ni. 
     
     
         7 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder is essentially free from Ni. 
     
     
         8 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder further comprises between 0.05% and 0.50% by weight of one or more of element(s) selected from the group of tungsten (W), titanium (Ti), niobium (Nb) and aluminium (Al). 
     
     
         9 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder consists of, in percentage by weight:
 Fe: Bal.   Mn: 0.09-0.3   Cr: 1.3-1.6   Mo: 0.15-0.3   and max 0.3 incidental impurities.   
     
     
         10 . A method according to any one of  claims 1   5 ,  claim 1 , wherein the pre-alloyed iron-based steel powder consists of, in percentage by weight:
 Fe: Bal.   Mn: 0.09-0.3   Cr: 1.5-1.9   Mo: max 0.1   and max 0.3 incidental impurities.   
     
     
         11 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder consists of, in percentage by weight:
 Fe: Bal.   Mn: 0.09-0.3   Cr: 2.8-3.2   Mo: 0.4-0.6   and max 0.3 incidental impurities.   
     
     
         12 . A method according to  claim 1 , wherein the pre-alloyed iron-based steel powder consists of, in percentage by weight:
 Fe: Bal.   Mn: 0.09-0.3   V: 0.05-0.4   Mo: max 0.1   and max 0.3 incidental impurities.   
     
     
         13 . A nitrated, sintered component, produced according to  claim 1 , and having a wear resistance in lubricating sliding contact that provides safe wear for hertzian pressures up to at least 800 MPa when tested at a sliding velocity of 2.5 m/s during 100 seconds. 
     
     
         14 . A nitrated, sintered component, produced according to  claim 1 , and having a wear resistance in lubricating sliding contact that provides safe wear for hertzian pressures up to at least 900 MPa, when tested at a sliding velocity of 2.5 m/s during 100 seconds. 
     
     
         15 . A nitrated, sintered component, produced according to  claim 1 , and having a wear resistance in lubricating sliding contact that provides safe wear for hertzian pressures up to at least 1000 MPa, when tested at a sliding velocity of 2.5 m/s during 100 seconds.