Submicron Cemented Carbide with Mixed Carbides

Abstract

A cemented carbide body is 1-30% by mass of binder consisting of Co, Co/Ni, Co/Fe, Co/Ni/Fe or Ni/Fe and a hard material having a hexagonal WC phase and having a face-centered cubic phase of the form (M 1 , M 2 , M 3 )C or (M 1 , M 2 , M 3 )(C, N) or (M 1 , M 2 , M 3 )(O, C, N) where M 1 =Ti and/or Zr and M 2 =W and M 3 optionally means none or one or a plurality of the elements Ta, Nb, Hf, Cr, Mo or V, wherein the proportion of the face-centered cubic phase based on the total mass is 2% to 97%, preferably 5 to 12% by mass, and the microstructure of the hexagonal phase and of the face-centered cubic phase has a mean grain size of between 0.2 μm and 1 μm, preferably ≦0.9 μm, and the mean grain sizes of the hexagonal phase and of the face-centered cubic phase differ at most by 30%.

1 . A cemented carbide body comprising 1-30% by mass of binder consisting of Co, Co/Ni, Co/Fe, Co/Ni/Fe or Ni/Fe and a hard material having a hexagonal WC phase and having a face-centered cubic phase of the form (M 1 , M 2 , M 3 )C or (M 1 , M 2 , M 3 )(C, N) or (M 1 , M 2 , M 3 )(O, C, N) where M 1 =Ti and/or Zr and M 2 =W and M 3  optionally means none or one or a plurality of the elements Ta, Nb, Hf, Cr, Mo or V, wherein the proportion of the face-centered cubic phase based on the total mass is 2% to 97%, preferably 5 to 12% by mass, and the microstructure of the hexagonal phase and of the face-centered cubic phase has a mean grain size of between 0.2 μm and 1 μm, preferably ≦0.9 μm, and the mean grain sizes of the hexagonal phase and of the face-centered cubic phase differ at most by 30%. 
     
     
         2 . The cemented carbide body as claimed in  claim 1 , characterized in that the face-centered cubic phase contains a carbonitride having a proportion of molar C of between 80% and 40% and a proportion of molar N of between 20% and 60%. 
     
     
         3 . The cemented carbide body as claimed in  claim 1 , characterized by an edge zone which is free from face-centered cubic carbides or carbonitrides. 
     
     
         4 . The cemented carbide body as claimed in  claim 1 , characterized in that:
 a) a carbonitride phase which is substantially free from binder phase, preferably completely free from binder phase, is present in an outer, first layer which adjoins the body surface and extends down to a depth of between 2 μm and 30 μm, said carbonitride phase;   b) being adjacent to an underlying middle layer having a thickness of 5 μm to 150 μm, which consists of a substantially pure WC—Co composition; and in that   c) in a third, lowermost layer having a thickness of at least 10 μm and at most 650 μm, the proportions of the binder phase and of the IVa and/or Va elements increase to the substantially constant value present in the interior of the body, and the proportion of tungsten decreases to the substantially constant value present in the interior of the body.   
     
     
         5 . The cemented carbide body as claimed in either of  claim 1 , characterized in that:
 a) in an outer layer which adjoins the body surface or an edge zone having a depth of penetration of 1 μm to at most 3 μm and extends down to a depth of between 10 μm and 200 μm, in the hard material phase, the proportion of tungsten and of the binder phase is at most 0.8 times the proportion arising from the overall composition, and in this layer the proportion of tungsten and of the binder phase increases substantially continuously toward the interior of the body and the proportion of nitrogen decreases substantially continuously toward the interior of the body;   b) in that in an underlying middle layer having a thickness of between 20 μm and 400 μm, the tungsten and binder phase contents pass through a maximum with an increasing depth of penetration, and the contents of elements of group IVa and/or Va of the periodic table run through a minimum; and   c) in that in a third, lowermost layer which extends down to a depth of penetration up to at most 1 mm, as measured from the body surface, the proportions of tungsten and binder phase decrease to substantially constant values in the interior of the body, and the contents of elements of group IVa and/or Va of the periodic table increase to substantially constant values.   
     
     
         6 . The cemented carbide body as claimed in  claim 1 , characterized in that:
 a) a first layer having a thickness of 2-100 μm is provided, having a proportion of binder metal of 2-25% by mass and comprising up to 25% by volume of nitrides or carbonitrides of one or a plurality of metals from group IVa of the periodic table and/or up to 10% by volume of carbides and/or carbonitrides of V, Nb, Ta and/or Cr, remainder WC;   b) a second layer which has a thickness of 2 to 40 μm and has a higher proportion of nitrogen than in the first layer is arranged underneath the first layer, said second layer consisting essentially of nitrides and/or carbonitrides of the metals from group IVa of the periodic table and containing proportions of up to 10% by volume of the elements W, Mo, V, Ta, Nb, Cr and up to 15% by mass of binder; and   c) in that a transition zone having a thickness of 2 to 100 μm is arranged underneath the second layer, in which transition zone the composition gradually changes to a homogeneous composition in the interior of the core of the cemented carbide or cermet body.   
     
     
         7 . A method for producing a cemented carbide body comprising 1-30% by mass of binder, which consists of Co and/or Ni, if appropriate additionally Fe, remainder hard material phase, consisting of at least one metal carbide or metal carbonitride, by mixing, grinding and initially pressing a green compact and finally sintering, characterized in that, in addition to the binder metal or the binder metals, the starting powder mixture contains a pre-alloyed phase of the type (M1, M2, M3)C or (M1, M2, M3)(C, N) or (M1, M2, M3)(O, C, N) where M1=Ti and/or Zr and M2=W and M3 optionally means none or one or a plurality of the elements Ta, Nb, Hf, Cr, Mo or V. 
     
     
         8 . The method as claimed in  claim 7 , characterized in that the pulverulent starting mixture for producing a cemented carbide body additionally contains hexagonal WC or a tungsten-containing phase, such as pure W, W2C or WO3, which reacts by the take up of carbon to form hexagonal WC. 
     
     
         9 . The method as claimed in  claim 7 , characterized in that the initially pressed green compact is subjected to reaction sintering, in which N2 is present in the gas atmosphere during the heating between 1100° C. and 1300° C. and, in accordance with the reaction equation
     a (M1, M2, M3)C+ b  W+ c  N2 →d (M1, M2, M3)(C, N)+ e  WC, 
 
       forms the desired carbonitride and carbide phases, where M1=Ti and/or Zr, M2=W and M3 (optionally) means one or a plurality of the elements Ta, Nb, Hf, Cr, Mo or V and a, b, c, d and e are the stoichiometric coefficients. 
     
     
         10 . The method as claimed in  claim 8 , characterized in that the green compact is heated in vacuo, preferably at 8° C./min, up to 1100° C., then N2 is admitted at a pressure of between 1 Pa and 107 Pa and the temperature of 1100° C. is retained for 15 to 30 min, before the green compact is heated further to 1300° C., preferably at a heating rate of 3° C./min, in that the temperature of 1300° C. is retained preferably for 15 min and the body is heated further up to the sintering temperature, preferably of 1450° C., the sintering temperature is retained for 30 min and the sintered body is finally cooled to room temperature, preferably at a cooling rate of 4° C./min. 
     
     
         11 . The method as claimed in one of  claim 7 , characterized in that the N2 atmosphere is also maintained during cooling at least until 1000° C. is reached. 
     
     
         12 . The method as claimed in one of  claim 7 , characterized in that, once cooling to at least 1000° C. has occurred, the sintered body is additionally treated in a nitrogen atmosphere at an N2 pressure of 5×103 Pa to 107 Pa at temperatures of between 1000° C. and a temperature below the eutectic, preferably below 1200° C. 
     
     
         13 . The method as claimed in one of  claim 7 , characterized in that at least some of the nitrogen is introduced by nitrides, carbonitrides and/or oxycarbonitrides of at least one of the metals V, Nb, Ta, Cr, Mo and W which are present in the starting mixture, or by means of solid carbonitrides. 
     
     
         14 . The method as claimed in one of  claim 7 , characterized in that pulverulent hard materials which have been obtained from recycled cemented carbide bodies are present at least partially in the starting powder mixture.