Preferentially binder enriched cemented carbide bodies and method of manufacture

Abstract

Cemented carbide substrates having substantially A or B type porosity and a binder enriched layer near its surface are described. A refractory oxide, nitride, boride, and/or carbide coating is deposited on the binder enriched surface of the substrate. Binder enrichment is achieved by incorporating Group IVB or VB transition elements. These elements can be added as the metal, the metal hydride, nitride or carbonitride.

What is claimed is: 
     
       1. A cemented carbide body formed by sintering a substantially homogeneous mixture of constituents comprising: a least 70 weight percent tungsten carbide; a metallic binder; a .[.metal.]. .Iadd.second .Iaddend.carbide selected from the group consisting of the Group IVB and VB transition metal carbides; said metal carbide being present in an amount less than the amount of tungsten carbide; said body having substantially A to B type porosity throughout said body; said metal carbide combined with said tungsten carbide forming a solid solution carbide; a .Iadd.first .Iaddend.layer of .Iadd.binder enriched and .Iaddend.at least partially solid solution carbide depleted material .[.near.]. .Iadd.beginning at and extending inwardly from .Iaddend.a peripheral surface of said body.Iadd., the content of said binder present in the first layer reaching between about 150 percent and about 300 percent of the average binder content of the cemented carbide body; and a hard dense refractory coating bonded to the peripheral surface of the cemented carbide body.Iaddend.. 
     
     
       2. A cemented carbide body according to claim 1 wherein said binder is selected from the group consisting of cobalt, nickel, iron and their alloys. .[.3. A cemented carbide body formed by sintering a substantially homogeneous mixture of constituents comprising: at least 70 weight percent tungsten carbide; a cobalt binder alloy; a metal carbide selected from the group consisting of the Group IVB and VB transition metal carbides; said metal carbide combined with said tungsten carbide forming a solid solution carbide; a layer of at least partially solid solution depleted material near a peripheral surface of said body; and wherein said cobalt binder alloy has an overall magnetic saturation value of less than 158 
     
     
        gauss-cm 3  /gm cobalt..]. .[.4.  A cemented carbide body according to claim 3 wherein said cobalt binder alloy has an overall magnetic saturation value of approximately 145 to 157 gauss-cm 3  /gm cobalt..]. .[.5. A cemented carbide body according to claim 3 wherein said cobalt binder alloy has an overall magnetic saturation value of less than 126 
     
     
        gauss-cm 3  /gm cobalt..]. 6. A cemented carbide body comprising: at least 70 weight percent .[.tugnsten.]. .Iadd.tungsten .Iaddend.carbide; cobalt; a metal carbide selected from the group consisting of the Group IVB and VB transition metal carbides; a layer of cobalt enrichment near a peripheral surface of said body; said body having substantially A to B type porosity throughout .Iadd.and wherein the cobalt enriched layer has a cobalt content at said peripheral surface equal to 1.5 to 3 times the 
     
     
        average cobalt content of the body.Iaddend.. 7. The cemented carbide, body according to claim 6 wherein the level of said transition metal carbide in 
     
     
        said layer of cobalt enrichment is at least partially depleted. 8. A cemented carbide body according to claims 6 or 7 wherein said metal carbide is selected from the group consisting of titanium .Iadd.carbide.Iaddend., hafnium .Iadd.carbide.Iaddend., tantalum 
     
     
        .Iadd.carbide ep and niobium .Iadd.carbide.Iaddend.. 9. A cemented carbide body according to claims 6 or 7 wherein said metal carbide is present at 
     
     
        the level of at least 0.5 weight percent. 10. A cemented carbide body according to claim 8 wherein said metal carbide is present at the level of 
     
     
        at least 0.5 weight percent. .[.11.  A cemented carbide body according to claims 6 or 7 wherein the cobalt enriched layer has a cobalt content at said peripheral surface equal to 1.5 to 3 times the average cobalt content of the body..]. .[.12. A cemented carbide body according to claim 6 wherein the cobalt enriched layer extends inwardly from said peripheral surface of said body to a minimum depth of substantially 6 microns..]. 
     
     
            A cemented carbide body according to claim .[.11.]. .Iadd.6 .Iaddend.wherein the cobalt enriched layer extends inwardly from said peripheral surface of said body to a minimum depth of substantially 6 microns. .[.14. A cemented carbide body according to claim 12 wherein the cobalt enriched layer extends inwardly from said peripheral surface of 
     
     
        said body to a depth of 12 to 50 microns..]. 15. A cemented carbide body according to claim 13 wherein the cobalt enriched layer extends inwardly from said peripheral surface of said body to a depth of 12 to 50 microns. 
     
     
         6. A cemented carbide body accoring to .[.claims 6 or 14.]. .Iadd.claim 6.Iaddend., wherein said peripheral surface of said body comprises a rake face; said rake face joined to a flank face; a cutting edge located at the junction of said rake and flank faces; and wherein said enriched layer 
     
     
        extends inwardly from said rake face. 17. A cemented carbide body according to claim 16 further comprising a hard dense refractory coating bonded to said peripheral surface of said body, and said coating having 
     
     
        one or more layers. 18. The cemented carbide body according to claim .[.17.]. .Iadd.100 .Iaddend.wherein the material comprising said layer is selected from the group consisting of the carbides, nitrides, borides and carbonitrides of titanium, zirconium, hafnium, niobium, tantalum, 
     
     
        vanadium, and the oxide and oxynitride of aluminum. 19. The cemented carbide body according to claim .[.17.]. wherein said coating comprises a 
     
     
        layer of titanium carbide. 20. The cemented carbide body according to claim .[.17.]. .Iadd.100 .Iaddend.wherein said coating comprises a layer 
     
     
        of titanium carbonitride. 21. The cemented carbide body according to claim .[.17.]. .Iadd.100 .Iaddend.wherein said coating comprises a layer of 
     
     
        titanium carbide and a layer of titanium nitride. 22. The cemented carbide body according to claim 21 wherein said coating further comprises a layer 
     
     
        of titanium carbonitride. 23. The cemented carbide body according to claim .[.17.]. .Iadd.100 .Iaddend.wherein said coating comprises a layer of 
     
     
        aluminum oxide. 24. The cemented carbide body according to claim 23 
     
     
        wherein said coating further comprises a layer of titanium carbide. 25. The product prepared by the process of forming a binder enriched layer near a peripheral surface of a substantially A to B type porosity cemented carbide body, in which said process comprises: milling and blending a first carbide powder, a binder alloy powder and a chemical agent powder selected from the group consisting of metals, alloys, nitrides and carbonitrides of Group IVB and VB transition metals; pressing a compact utilizing said powders; sintering said compact at a temperature above the binder alloy melting temperature so as to transform, at least partially, the chemical agent to a carbide in the layer to be binder enriched; removing said binder enriched layer in selected areas of said product; resintering said compact at a temperature above the binder alloy melting temperatures so as to transform, at least partially, the chemical agent to a carbide in the layer near the peripheral surface of the selected area of 
     
     
        the product. 26. The product of claim 25 further comprising the step of: depositing on said peripheral surface of the product an adherent hard wear 
     
     
        resistant refractory coating having one or more layers. 27. The product of claim 26 wherein the material comprising each of said layers is selected from the group consisting of the carbides, nitrides and carbonitrides of titanium, zirconium, hafnium, niobium, tantalum and vanadium, and the 
     
     
        oxide and oxynitride of aluminum. 28. The product of claim 25 wherein said first carbide powder comprises tungsten carbide and said tungsten carbide 
     
     
        comprises at least 70 weight percent of the product. 29. The product according to claim 28 wherein said binder is selected from the group 
     
     
        consisting of cobalt, nickel, iron and their alloys. 30. A process for forming a cobalt binder enriched layer near a peripheral surface of a substantially A type porosity cemented carbide body, said process comprising the steps of: milling and blending powders comprising tungsten carbide, cobalt and a metal compound selected from the group consisting of nitrides, and carbonitrides of Group IVB and VB transition metals.Iadd., and the adding of free carbon as during milling and blending in an amount sufficient to produce a tungsten lean cobalt binder in the sintered compact.Iaddend.; pressing a compact utilizing said powders; sintering said compact at a temperature above the melting temperature of said binder so as to transform, at least partially, the metal compound to a metal carbide in the layer to be binder enriched.Iadd.; and removing said binder enriched layer in selected areas of said peripheral surface.Iaddend.. .[.31. The process according to claims 30 further comprising the step of: removing said binder enriched layer in selected areas of said peripheral 
     
     
        surface..]. 32. The process according to claim 30 further comprising the step of: depositing on said peripheral surface an adherent hard wear resistant coating having one or more layers wherein the material comprising each of said layers is selected from the group consisting of the carbides, nitrides, borides and carbonitrides of titanium, zirconium, hafnium, niobium, tantalum and vanadium, and the oxide and the oxynitride 
     
     
        of aluminum. 33. The process according to claim 30 wherein said powders further comprise a second carbide powder selected from the group consisting of the Group IVB and VB metal carbides and their solid 
     
     
        solutions. 34. The process according to claim 30 further comprising the step of at least partially volatilizing an element selected from the group 
     
     
        consisting of hydrogen and nitrogen during the sintering step. .[.35.  The process according to claim 31 further comprising the addition of free carbon as during milling and blending in an amount sufficient to produce a 
     
     
        tungsten lean cobalt binder in the sintered compact..]. .Iadd.36.  The cemented carbide body according to claim 1 wherein said binder is present 
     
     
        in an amount up to about 10 weight percent. .Iaddend. .Iadd.37.  A cemented carbide body according to claim 1 further including nitrogen present as a carbonitride in a solid solution of said tungsten and second carbide. .Iaddend. .Iadd.38. A cemented carbide body according to claim 37 wherein said carbonitride is a tungsten titanium carbonitride. .Iaddend. 
     
     
        .Iadd.39.  A cemented carbide body according to claim 1 wherein said second carbide is present at the level of at least 0.5 weight percent. 
     
     
        .Iaddend. .Iadd.40.  A cemented carbide body according to claim 1 wherein said second carbide is present in an amount between 0.5 and 2 weight 
     
     
        percent. .Iaddend. .Iadd.41.  The cemented carbide body according to claim 1 further including a second layer of partial metallic binder depletion beneath and separate from said first layer. .Iaddend. .Iadd.42. The cemented carbide body according to claim 41 wherein the bulk substrate is beneath said second layer. .Iaddend. .Iadd.43. The cemented carbide body according to claim 1 wherein said first layer extends inwardly from the peripheral surface a distance between about 12 microns to about 50 microns. .Iaddend. .Iadd.44. The cemented carbide body according to claim 1 wherein the first layer extends inwardly from the peripheral surface a 
     
     
        distance between about 6 and about 125 microns. .Iaddend. .Iadd.45.  The cemented carbide body according to claim 1 wherein said second carbide is a cubic carbide selected from the group consisting of tantalum carbide, niobium carbide, titanium carbide, vanadium carbide, hafnium carbide and zirconium carbide. .Iaddend. .Iadd.46. The cemented carbide body according to claim 45 wherein the metallic binder is cobalt, and the cobalt is present in an amount between about 5 and 10 weight percent. .Iaddend. .Iadd.47. The cemented carbide body according to claim 46 wherein the cubic carbide content is not greater than about 20 weight percent. 
     
     
        .Iaddend. .Iadd.48.  The cemented carbide body according to claim 1 wherein the binder is cobalt, and the first layer has a cobalt content between about 1.75 and about 3.0 times the average cobalt content of the 
     
     
        cemented carbide body. .Iaddend. .Iadd.49.  The cemented carbide body according to claim 1 wherein said metallic binder is cobalt and said cobalt is present as a cobalt binder alloy, and said cobalt binder alloy has an overall magnetic saturation value of between approximately 145 to 
     
     
        approximately 157 gauss-cm -3  /gm cobalt. .Iaddend. .Iadd.50.  The cemented carbide body according to claim 1 wherein the first layer has a binder content between about 2.0 and about 3.0 times the average binder 
     
     
        content of the cemented carbide body. .Iaddend. .Iadd.51.  The cemented carbide body according to claim 1 wherein said binder is cobalt and the cobalt is present in said body as a cobalt alloy, and said cobalt alloy has an overall magnetic saturation value of less than 158 gauss-cm -3   
     
     
        /gm cobalt. .Iaddend. .Iadd.52.  A cemented carbide body according to claim 6 wherein the cobalt enriched layer has a cobalt content reaching between about 1.75 and about 3.0 times the average cobalt content of the body. .Iaddend. .Iadd.53. A cemented carbide body according to claim 6 wherein the cobalt enriched layer has a cobalt content reaching between about 2.0 and about 3.0 times the average cobalt content of the body. 
     
     
        .Iaddend. .Iadd.54.  The cemented carbide body according to claim 6 wherein said cobalt is present as a cobalt binder alloy having an overall magnetic saturation value of less than 158 gauss-cm -3  /gm cobalt and 
     
     
        at least gauss-cm 3  /gm cobalt. .Iaddend. .Iadd.55.  The product of claim 25 wherein in said cemented carbide body said binder alloy is a cobalt alloy, and said cobalt alloy has an overall magnetic saturation value of between approximately 145 to approximately 157 gauss-cm -3   
     
     
        /gm cobalt. .Iaddend. .Iadd.56.  A coated cemented carbide cutting insert comprising: a cemented carbide body configured so as to present a rake face joined to a flank face, a cutting edge located at the juncture of the rake and flank faces;   said cemented carbide body formed by sintering a substantially homogenous mixture of constituents, the body comprising:   at least 70 weight percent of tungsten carbide;   between about 3 weight percent and about 10 weight percent of cobalt;   a solid solution of tungsten carbide and a carbide of a second metal, the second metal selected from the group consisting of titanium, hafnium, tantalum and niobium;   a zone of cobalt enrichment being at and extending inwardly from the peripheral surface of the rake face wherein the zone of cobalt enrichment has a cobalt content equal to about 1.5 to about 3 times the average cobalt content of the cemented carbide body, cobalt enrichment being absent from the flank face, said cobalt being present as a cobalt binder alloy wherein said cobalt binder alloy has an overall magnetic saturation value of less than 158 gauss-cm 3  /gm cobalt; and   a hard dense refractory coating bonded to the peripheral surfaces of said cemented carbide body including the peripheral surfaces of the rake and flank faces, and said coating having one or more layers. .Iaddend.   
     
     
        .Iadd.  .  The cutting insert according to claim 56 wherein said coating comprises a layer of titanium carbide. .Iaddend. .Iadd.58. The cutting insert according to claim 56 wherein said coating comprises a layer of titanium carbonitride. .Iaddend. .Iadd.59. The cutting insert according to claim 56 wherein said coating comprises a layer of titanium nitride. .Iaddend. .Iadd.60. The cutting insert according to claim 56 wherein said coating comprises a layer of aluminum oxide. .Iaddend. .Iadd.61. The cutting insert according to claim 56 wherein the zone of cobalt enrichment further exhibits solid solution carbide depletion to some degree. .Iaddend. .Iadd.62. The cutting insert according to claim 61 wherein the cemented carbide body exhibits an absence of solid solution carbide depletion from the flank face. .Iaddend. .Iadd.63. The cutting insert according to claim 56 wherein the cemented carbide body includes a zone of cobalt depletion to some degree and solid solution enrichment beneath the 
     
     
        zone of cobalt enrichment. .Iaddend. .Iadd.64.  The cutting insert according to claim 56 wherein the cobalt enriched zone extends inwardly from the peripheral surface of the rake face to a minimum depth of approximately 6 microns. .Iaddend. .Iadd.65. The cutting insert according to claim 56 further including nitrogen present as a carbonitride in a solid solution of the tungsten carbide and second metal carbide. .Iaddend. 
     
     
        .Iadd.66.  The cutting insert according to claim 56 wherein said cobalt binder alloy has an overall magnetic saturation value of between approximately 145 to approximately 157 gauss-cm 3  /gm cobalt. 
     
     
        .Iaddend. .Iadd.67.  The cutting insert according to claim 56 wherein the zone of cobalt enrichment reaches a level of between about 175 percent and about 300 percent of the average cobalt content of the cemented carbide body. .Iaddend. .Iadd.68. The cutting insert according to claim 56 wherein the zone of cobalt enrichment reaches a level of between about 200 percent and about 300 percent of the average cobalt content of the cemented 
     
     
        carbide body. .Iaddend. .Iadd.69.  The coated cemented carbide cutting insert according to claim 56 wherein said cobalt binder alloy has an overall magnetic saturation value of less than 158 gauss-cm 3  /gm 
     
     
        cobalt and at least 139 gauss-cm 3  /gm cobalt. .Iaddend. .Iadd.70.  A process for forming a cobalt enriched layer at a peripheral surface of a cemented carbide body, said process comprising the steps of: obtaining a compact having a substantially uniform distribution of a first carbide, an amount between about 3 and about 10 weight percent of cobalt, and an amount greater than approximately 0.5 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of transition metals whose carbides have a free energy of formation more negative than said first carbide at a temperature above the binder carbon eutectic;   densifying said compact;   transforming, at least partially, said chemical agent to a solid solution with said first carbide by a heat treatment; and   increasing the cobalt content at said peripheral surface during said heat treatment resulting in the cemented carbide body having a cobalt enriched layer beginning at and extending inwardly from the peripheral surface wherein the cobalt content in the cobalt enriched layer is between about 150 percent and about 300 percent of the average cobalt content of the cemented carbide body, and the cobalt being present as a cobalt binder alloy wherein the cobalt binder alloy has a magnetic saturation value of   
     
     
        less than 158 gauss-cm 3  /gm cobalt. .Iaddend. .Iadd.71.  The process according to claim 70 wherein the chemical agent is present in an amount 
     
     
        between 0.5 and 2 weight percent. .Iaddend. .Iadd.72.  The process according to claim 70 whereim the chemical agent is titanium nitride. .Iaddend. .Iadd.73. The process according to claim 70, wherein the 
     
     
        chemical agent is titanium carbonitride. .Iaddend. .Iadd.74.  The process according to claim 70 wherein said cobalt binder alloy has an overall magnetic saturation value of between approximately 145 to approximately 
     
     
        157 gauss-cm -3  /gm cobalt. .Iaddend. .Iadd.75.  The process according to claim 70 wherein said cobalt binder alloy has an overall magnetic saturation value of less than 158 gauss-cm -3  /gm cobalt and at least 
     
     
        139 gauss-cm 3  /gm cobalt. .Iaddend. .Iadd.76.  A process for forming a binder enriched layer near a peripheral surface of a cemented carbide body, said process comprising the steps of: obtaining a compact having a substantially uniform distribution of a first carbide, an amount between about 3 and about 10 weight percent of a binder metal, and an amount greater than approximately 0.5 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of transition metals whose carbides have a free energy of formation more negative than said first carbide at a temperature above the binder carbon eutectic:   densifying said compact;   transforming, at least partially, said chemical agent to a solid solution with said first carbide by a first heat treatment;   increasing the binder content near said peripheral surface during said first heat treatment;   removing the zone of increased binder content from at least a portion of the peripheral surface of the body;   subjecting the cemented carbide body to a second heat treatment so as to increase the binder content near the portion of the peripheral surface   
     
     
        previously removed. .Iaddend. .Iadd.77.  The process according to claim 76 further including the step of applying a hard dense refractory coating to 
     
     
        the body. .Iaddend. .Iadd.78.  A process for fabricating a cutting insert said process comprising the steps of: obtaining a compact having a substantially uniform distribution of a first carbide, an amount not greater than about 10 weight percent of a binder metal, and an amount greater than approximately 0.5 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of transition metals whose carbides have a free energy of formation more negative than said first carbide at a temperature above the binder carbon eutectic;   densifying said compact into a configuration presenting a rake face joined to a flank face wherein a cutting edge is located at the juncture of the rake and flank faces;   transforming, at least partially, said chemical agent to solid solution with said first carbide by a first heat treatment while maintaining some nitrogen in the form of a nitride or carbonitride as a constituent of the compact;   increasing the binder content near said peripheral surface of the rake and flank faces during said first heat treatment;   removing the binder enriched layer from at least one portion of the peripheral surface of the compact;   subjecting the compact to a second heat treatment so as to increase the binder content near the one portion of the peripheral surface of the compact; and   depositing on said peripheral surface of the cemented carbide body an adherent hard wear resistant coating having one or more layers wherein the material comprising each of said layers is selected from the group consisting of the carbides, nitrides, borides and carbonitrides of titanium, zirconium, hafnium, niobium, tantalum and vanadium, and the   
     
     
        oxide and the oxynitride of aluminum. .Iadd.79.  The process according to claim 78 wherein the chemical agent is present in an amount between 0.5 and 2 weight percent. .Iaddend. .Iadd.80. The process according to claim 78 wherein a portion of the nitrogen present in the compact prior to the first heat treatment is volatilized during the first heat treatment. 
     
     
        .Iaddend. .Iadd.81.  The process according to claim 80 wherein a portion of the nitrogen present in the compact after the first heat treatment and prior to the second heat treatment is volatilized during the second heat treatment. .Iaddend. .Iadd.82. The process according to claim 78 wherein the first and second heat treatments occur at a temperature over the melting point of the binder metal. .Iaddend. .Iadd.83. The process according to claim 78 wherein the transition metals include titanium, tantalum, hafnium and niobium. .Iaddend. .Iadd.84. The process according to claim 78 further comprising the addition of free carbon as during milling and blending in an amount sufficient to produce a tungsten lean 
     
     
        cobalt binder in the sintered compact. .Iaddend. .Iadd.85.  The process according to claim 84 wherein one-half mole of the free carbon is added 
     
     
        per mole of starting nitrogen. .Iaddend. .Iadd.86.  The process according to claim 78 wherein the chemical agent is titanium nitride. .Iaddend. .Iadd.87. The process according to claim 78 wherein the binder enrichment is removed from an area adjacent the peripheral surface of the flank face after the first heat treatment and before the second heat treatment. 
     
     
        .Iaddend. .Iadd.88.  A process for fabricating a coated cemented carbide cutting insert, said process comprising the steps of: obtaining a compact having a substantially uniform distribution of a first carbide, an amount of binder metal not greater than about 10 weight percent; and an amount between approximately 0.5 and 2 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of the Group IVB and VB transition metals;   densifying said compact into a configuration presenting a rake face joined to a flank face wherein a cutting edge is located at the juncture of the rake and flank faces;   liquid phase sintering the configured compact in an atmosphere having the nitrogen vapor pressure below its equilibrium pressure so as to transform, at least partially, said chemical agent to solid solution with said first carbide while maintaining some nitrogen in the form of a nitride or carbonitride as a constituent of the compact;   increasing the binder content of the compact in a zone near the peripheral surface of the rake and flank faces during the liquid phase sintering;   removing the binder enriched zone from at least one portion of the peripheral surface of the compact;   subjecting the compact to a heat treatment in an atmosphere having the nitrogen vapor pressure below its equilibrium vapor pressure so as to increase the binder content near the one portion of the peripheral surface of the compact; and   depositing on said peripheral surface of the cemented carbide compact an adherent hard wear resistant coating having one or more layers wherein the material comprising each of said layers is selected from the group consisting of the carbides, nitrides borides and carbonitrides of titanium, zirconium, hafnium, niobium, tantalum and vanadium, and the oxide and the oxynitride of aluminum. .Iaddend. .Iadd.89. The process according to claim 88 wherein the pressure during the liquid phase sintering and the heat treatment is between about 0.1 and about 0.15 torr. .Iaddend. .Iadd.90. A cemented carbide body of substantially A to B porosity and having a binder enriched zone at the peripheral surface of the body produced by a process comprising the steps of:   obtaining a compact having a substantially uniform distribution of a first carbide, an amount between about 3 and about 10 weight percent of a binder metal, and an amount greater than approximately 0.5 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of transition metals whose carbides have a free energy of formation more negative than said first carbide at a temperature above the binder carbon eutectic;   densifying said compact;   transforming, at least partially, said chemical agent to a solid solution with said first carbide by a heat treatment; and   increasing the binder content in a zone at said peripheral surface during said heat treatment wherein the level of cobalt in the zone is between about 175 percent and about 300 percent of the average cobalt content of   
     
     
        the cemented carbide body. .Iaddend. .Iadd.91.  The cemented carbide body according to claim 90 wherein the transforming step includes: liquid phase sintering the compact in an atmosphere wherein the nitrogen partial pressure is below its equilibrium vapor pressure. .Iaddend.   
     
     
        .Iadd. 2.  The cemented carbide body according to claim 90 wherein the level of binder in the zone reaches a level of between about 200 percent and about 300 percent of the average binder content of the cemented 
     
     
        carbide body. .Iaddend. .Iadd.93.  The cemented carbide body according to claim 90 wherein said binder metal is cobalt and said cobalt is present as a cobalt binder alloy, and said cobalt binder alloy has an overall magnetic saturation value of less than 158 gauss-cm 3  /gm cobalt and 
     
     
        at least 139 gauss-cm 3  /gm cobalt. .Iaddend. .Iadd.94.  A cemented carbide body having a binder enriched zone near the peripheral surface of the body produced by a process comprising the steps of: obtaining a compact having a substantially uniform distribution of a first carbide, an amount between about 3 and about 10 weight percent of a binder metal, and an amount greater than approximately 0.5 weight percent of a chemical agent selected from the group consisting of the nitrides and carbonitrides of transition metals whose carbides have a free energy of formation more negative than said first carbide at a temperature above the binder carbon eutectic;   densifying said compact;   transforming, at least partially, said chemical agent to a solid solution with said first carbide by a first heat treatment comprising liquid phase sintering the compact in an atmosphere wherein the nitrogen partial pressure is below its equilibrium vapor pressure;   increasing the binder content in a zone near said peripheral surface during said first heat treatment;   removing the binder enriched zone at selected areas of the peripheral surface; and   subjecting the compact to a second heat treatment in an atmosphere wherein the nitrogen partial pressure is below its equilibrium vapor pressure so as to increase the binder content near the selected areas of the peripheral surface. .Iaddend. .Iadd.95. The cemented carbide body according to claim 94 further comprising the step of coating the peripheral surface of the cemented carbide body with a hard dense refractory coating after the second heat treatment. .Iaddend. .Iadd.96. The cemented carbide body according to claim 94 further comprising the step of coating the peripheral surface of the cemented carbide body with a hard dense refractory coating. .Iaddend. .Iadd.97. A coated cemented carbide cutting insert comprising:   a cemented carbide body configured so as to present a rake face joined to a flank face, a cutting edge located at the juncture of the rake and flank faces, the body comprising:   at least 70 weight percent tungsten carbide;   between about 3 weight percent and about 10 weight percent of cobalt, said cobalt being present as a cobalt binder alloy, said cobalt binder alloy having an overall magnetic saturation value between about 145 and about 157 gauss-cm 3  /gm cobalt;   a solid solution of tungsten carbide and a carbide of a second metal wherein said second metal is selected from the group consisting of titanium, hafnium, tantalum and niobium;   a zone of cobalt enrichment being at and extending inwardly from a ground peripheral surface of a selected one of the faces, the cobalt content in the zone of cobalt enrichment reaching between about 150 percent and about 300 percent of the average cobalt content of the cemented carbide body; and   a hard dense refractory coating bonded to the peripheral surface of the   
     
     
        cemented carbide body. .Iaddend. .Iadd.98.  The coated cemented carbide cutting insert according to claim 97 wherein the rake face has a ground 
     
     
        peripheral surface. .Iaddend. .Iadd.99.  The coated cemented carbide cutting insert of claim 97 wherein the cobalt content in the zone of cobalt enrichment ranges between about 200 percent and about 300 percent of the average cobalt content of the cemented carbide body. .Iaddend. 
     
     
        .Iadd.100.  A cemented carbide body comprising at least 70 weight percent tungsten carbide; cobalt; a metal carbide selected from the group consisting of the Group IVB and VB transition metal carbides; a layer of cobalt enrichment near a peripheral surface of said body wherein the cobalt enriched layer extends inwardly from said peripheral surface of said body to a depth of 12 to 50 microns and wherein the cobalt content in the cobalt enriched layer reaches between about 150 percent and about 300 percent of the average cobalt content of the cemented carbide body; said body having substantially A to B type porosity throughout; said peripheral surface of said body comprises a rake face; said rake face joined to a flank face; a cutting edge located at the juncture of said rake and flank faces; and wherein said enriched layer extends inwardly from said rake face; a hard dense refractory coating bonded to said peripheral surface of said body, and said coating having one or more layers. .Iaddend. 
     
     
        .Iadd.      The cemented carbide body according to claim 100 wherein said cobalt is present as a cobalt binder alloy which has an overall magnetic saturation value of between approximately 145 to approximately 157 
     
     
        gauss-cm -3  /gm cobalt. .Iaddend. .Iadd.102.  The cemented carbide body according to claim 100 wherein the cobalt content in the cobalt enriched layer reaches a level between about 175 percent and about 300 percent of the average cobalt content of the cemented carbide body. 
     
     
        .Iaddend. .Iadd.103.  The cemented carbide body according to claim 100 wherein the cobalt content in the cobalt enriched layer reaches a level between about 200 percent and about 300 percent of the average cobalt 
     
     
        content of the cemented carbide body. .Iaddend. .Iadd.104.  The cemented carbide body according to claim 100 wherein said cobalt is present in a cobalt binder alloy having an overall magnetic saturation value of less than 158 gauss-cm 3  /gm cobalt and at least 139 gauss-cm 3  /gm 
     
     
        cobalt. .Iaddend. .Iadd.105.  A cemented carbide body comprising: at least 70 weight percent tungsten carbide; cobalt; a metal carbide selected from the group consisting of the Group IVB and VB transition metal carbides; a layer of cobalt enrichment near a peripheral surface of said body wherein the level of cobalt enrichment in the cobalt enriched layer reaches 150 to 300 percent the average cobalt content of the body; said body having 
     
     
        substantially A to B type porosity throughout. .Iaddend. .Iadd.106.  The cemented carbide body according to claim 105 wherein said cobalt is present as a cobalt binder alloy which has an overall magnetic saturation value of between approximately 145 to approximately 157 gauss-cm -3   
     
     
        /gm cobalt. .Iaddend. .Iadd.107.  The cemented carbide body according to claim 105 wherein said cobalt is present as a cobalt binder alloy having an overall magnetic saturation value of less than 158 gauss-cm 3  /gm cobalt and at least 139 gauss-cm 3  /gm cobalt. .Iaddend.