SINTERED CEMENTED CARBIDE BODY AND USE THEREOF

Abstract: Sintered cemented carbide bodies are described, comprising at least one hard component and a Co-Ni-Fe binder which comprises about 40 to 90 wt.% cobalt, the remainder of the binder consisting of nickel and iron, apart from incidental impurities, with nickel comprising at least 4 but no more than 36 wt.% of the binder and iron comprising at least 4 but no more than 36 wt.% of the binder, and the binder having a Ni:Fe ratio of about 1.5:1 to 1:1.5. For achieving an improvement in mechanical properties, more particularly toughness and fatigue resistance, of the sintered cemented carbide bodies, it is proposed that the concentration of the binder has a gradient within the cemented carbide body.

Description: Sintered Cemented Carbide Body and Use Thereof The invention relates to a sintered cemented carbide body (cermet) , comprising at least one hard component and a cobalt-nickel-iron binder comprising about 40 to 90 wt.% cobalt, the remainder of the binder consisting of nickel and iron, apart from incidental impurities, with nickel comprising at least 4 but no more than 36 wt.% of the binder and iron comprising at least 4 but no more than 36 wt.% of the binder, and the binder having a Ni : Fe ratio of about 1.5:1 to 1:1.5. Sintered cemented carbide bodies (cermets) of this type are described in International Patent Applications published as WO 99/10549, WO 99/10550, WO 99/10551, WO 99/10552 and WO 99/10553. The aforementioned International Patent Applications furthermore describe the use of these sintered cemented carbide bodies as cutting inserts and cutting bits and for manufacturing drills and cemented carbide tools and tool inserts of all kinds . The entire content of said international patent applications hereby is expressly incorporated herein by reference. Whenever used herein, the term "cermet" refers to those materials, only, which comprise at least one metallic phase and at least one ceramic phase such as tungsten carbide (WC) . Diamond and graphite per se are not considered to be "ceramic", in the language of the present application. Thus, materials comprising diamond or graphite embedded in a metal matrix or bonded with a metal alloy do not form a "cermet" in the sense of the present invention. It is known from German Patent No. 32 11 047 and from U.S. Patent Re. 34,180 that in the case of cemented carbides comprising a binder consisting of cobalt, nickel or iron, under certain sintering conditions and after the addition of specific additives to the hard component powder blends, a binder enriched layer which however is at the same time depleted in or free of solid solution carbides will form near the surfaces of the sintered cemented carbide bodies, while a binder depleted layer which however is at the same time enriched in solid solution carbides will form beneath the enriched layer . It is the object of the present invention to provide novel sintered cemented carbide bodies which comprise a binder consisting of cobalt, nickel and iron, but which, compared with presently available cermets having Co-Ni-Fe binders, exhibit improved mechanical properties, in particular an enhanced fatigue resistance and at the same time an enhanced toughness . This object is achieved in accordance with the invention in a sintered cemented carbide body of the initially defined species in that the concentration of the Co-Ni-Fe binder has a gradient within the cemented carbide body and that the Co-Ni-Fe binder has a face centered cubic structure and does not experience phase transformations induced by tension, strain or other stresses. The concentration of the Co-Ni-Fe binder preferably has a gradient which increases from the interior of the cemented carbide body toward the surfaces thereof. This gradient material is surprising to a person of ordinary skill in the art because it was unexpected that the three-component binder consisting of cobalt, nickel and iron, which preferably is present in the form of an alloy but does not necessarily have to be present as an alloy, would display a behavior similar to that of the cobalt binder frequently used in the past. Above all, it could not be expected that a distribution of the binder in the sintered cemented carbide as described above would result. It is particularly advantageous if the Co-Ni-Fe binder is enriched in a zone ("binder enriched zone", BEZ) near the surface of the- cemented carbide body. The binder enriched zone (BEZ) is preferably located at a depth of up to 40 μm as measured from the surface of the cemented carbide body. In a preferred embodiment of the sintered cemented carbide body in accordance with the invention, the ratio of the constituents of the binder among each other (Co:Ni:Fe) is the same within the enriched zone (BEZ) in the binder as that outside of the enriched zone (BEZ) in the binder. In this embodiment the diffusion of the binder into the enriched zone proceeds in a congruent manner, i.e. without a change in the composition of the binder. This, too, was surprising to a person of ordinary skill in the art because in complicated multi-component systems an incongruent behavior of the constituents of the binder alloy is the rule more often than not . The Co-Ni-Fe binder of the sintered cemented carbide body in accordance with the invention has a face centered cubic structure and does not experience phase transformations induced by tension, strain or other stresses. The Co-Ni-Fe binder is substantially austenitic. Preferably, the proportion of the binder in the sintered cemented carbide amounts to 4 to 10 wt.%. The at least one hard component is preferably selected from the carbides, nitrides, carbonitrides , their mixtures, and their solid solutions, in any desired combination. Especially preferred hard components are the carbides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, as well as mixtures of a plurality of these carbides. Of the carbonitrides , those of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, as well as their mixtures are preferred as hard components . The sintered cemented carbide bodies in accordance with the invention are preferably used as cutting inserts, indexable inserts and for the production of cemented carbide tools and tool inserts of all kinds . The invention will now be explained in greater detail with reference to examples in conjunction with the drawings. Figures 1 to 3 are energy dispersion spectra (EDS) of the Co-Ni-Fe binders of the sintered cemented carbide bodies which have been made in accordance with Examples 1 to 3. In the Figures, the K- lines of the three elements, Co, Ni and Fe, of the respective binder alloy show the concentrations of the elements as a function of the layer depth, i.e. the distance from a surface of the sintered cemented carbide body. Example 1 First, a powder blend consisting of 94 wt.% hard components and 6 wt.% binder metal is prepared in accordance with common powder metallurgy methods. The powder blend had the following composition (in wt.%, respectively, as related to the overall amount of the powder blend) : 86.5% WC of a particle size of 5.0 μm 5.0% Ta(Nb)C 70/30 1.8% TiCN 70/30 0.7% TiC 3.6% Co 1.2% Ni 1.2% Fe Since the hard component mixture contains 1.8% titanium carbonitride, this composition is referred to by those of ordinary skill in the art as having a "nitrogen enrichment" in the powder blend. From this powder blend cuboid-shaped cutting insert blanks (green bodies) were then made in a conventional manner and were compressed to form compacts. The compacts were sintered and/or hot isostatically pressed, preferably using the known "sinter HIPping" process, at temperatures between approx. 1300 and 1760 °C, preferably between approx. 1400 and 1600 °C, and under pressures between approx. 1.7 and 206 MPa.. Sintering is preferably performed under a reduced pressure or in an inert gas atmosphere or a reducing gas atmosphere, with special temperature-time cycles being applied. The sintered cemented carbide body made in this way had the following physical properties : Density: 13.96 g/cm3 Magnetic saturation: 114 [47rσ] Magnetic field strength (He) : 99 [Oe] Vickers hardness (HV30) : 1510 Porosity: <A02 e.B (The porosity of cemented carbides is classified as follows in accordance with ASTM: Type A pores smaller than 10 μm in diameter; Type B pores between 10 and 40 μm in diameter; Type C irregular pores caused by free carbon.) The distribution of the three elements of the binder alloy and their concentration gradient which in each case increases from the interior of the body in the direction toward the surface thereof is apparent from Figure 1. The binder enrichment is located in a zone of a depth of up to about 40 μm (distance from the original surface) (cf . Figure 1) . Example 2 A powder blend of the following composition was prepared: 86.5% WC (mean particle size of 5.0 μm) 5.0% Ta(Nb)C 70/30 2.5% TiC 3.6% Co 1.2% Ni 1.2% Fe This powder blend was used to make sintered cemented carbide bodies, as described in Example 1. In this case the hard component mixture did not contain carbonitride, but only carbides, which is why the hard component mixture is referred to as having a "carbon enrichment" (C content in excessive stoichiometric ratio) . The physical properties of the sintered cemented carbide bodies made in this way were as follows : Density: 13.87 g/cm 3 Magnetic saturation: 118 [47rσ] Magnetic field strength (He) : 103 [Oe] Vickers hardness (HV30) : 1510 Porosity: <A02 e.B C06. Figure 2 shows the distribution of the elements in the binder alloy of the cermets thus made. A zone free of free carbon was determined at a depth between approx. 150 and 250 μm. Example 3 A powder blend of the following composition was prepared: 86.5% WC (mean particle size of 5.0 μm) 5..0% Ta(Nb)C 70/30 2. .0% TiC 0. .5% TiCN 70/30 3. .6% Co 1. .2% Ni 1. .2% Fe Apart from a C content in an excessive stoichiometric ratio, in this case the hard component mixture contained both titanium carbonitride and titanium carbide and furthermore tantalum niobium carbide, besides tungsten carbide as the main constituent. Sintered cemented carbide bodies were made from this powder blend, as described in Example 1. The physical properties of these bodies were as follows : Density: 13.88 g/cm3 Magnetic saturation: 117 [47rσ] Magnetic field strength (He) : 99 [Oe] Vickers hardness (HV30) : 1530 Porosity: <A02 e.B C06 The binder concentration gradient for these cermets is illustrated in Figure 3. In this case a solid solution carbide depleted zone was determined at a distance of between 5 and 10 μm from the original surface of the sintered cemented carbide bodies, while a zone free of free carbon was present at a depth between 150 and 300 μm. The sintered cemented carbide bodies in accordance with the invention can be provided with adherent coatings in a conventional manner (PVD, CVD) .

Claims: Claims 1. A sintered cemented carbide body, comprising at least one hard component and a Co-Ni-Fe binder comprising about 40 to 90 wt.% cobalt, the remainder of the binder consisting of nickel and iron, apart from incidental impurities, with nickel comprising at least 4 but no more than 36 wt.% of the binder and iron comprising at least 4 but no more than 36 wt.% of the binder, and the binder having a Ni : Fe ratio of about 1.5:1 to 1:1.5, characterized in that the concentration of the Co-Ni-Fe binder has a gradient within the cemented carbide body and that the Co-Ni-Fe binder substantially has a face centered cubic structure and does not experience phase transformations induced by tension, strain or other stresses. 2. The sintered cemented carbide body of claim 1, characterized in that the concentration of the Co-Ni-Fe binder has a gradient which increases from the interior of the cemented carbide body toward the surfaces thereof . 3. The sintered cemented carbide body of claim 1 or 2 , characterized in that the Co-Ni-Fe binder is enriched in a zone (BEZ) near the surface of the cemented carbide body. 4. The sintered cemented carbide body of claim 3 , characterized in that the enriched zone (BEZ) is located at a depth of up to about 40 μm as measured from the surface of the cemented carbide body. 5. The sintered cemented carbide body of any of claims 1 to 4, characterized in that the ratio of the constituents of the binder among each other (Co:Ni:Fe) is the same within the enriched zone (BEZ) in the binder as that outside of the enriched zone (BEZ) in the binder. 6. The sintered cemented carbide body of any of claims 1 to 5, characterized in that the Co-Ni-Fe binder is substantially austenitic. 7. The sintered cemented carbide body of any of claims 1 to 6, characterized in that the proportion of the binder in the sintered cemented carbide amounts to 4 to 10 wt.%. 8. The sintered cemented carbide body of any of claims 1 to 7 , characterized in that the at least one hard component is selected from the group consisting of carbides, nitrides, carbonitrides, their mixtures, and their solid solutions . 9. The sintered cemented carbide body of claim 8, characterized in that the at least one hard component comprises at least one carbide which is selected from the carbides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and/or tungsten. 10. The sintered cemented carbide body of claim 8, characterized in that the at least one hard component comprises at least one carbonitride which is selected from the carbonitrides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and/or tungsten. 11. Use of a sintered cemented carbide body according to any of claims 1 to 10 as a cutting insert, an indexable insert or for the production of cemented carbide tools and tool inserts .

Inventors: HEINRICH HANS-WILM, SCHMIDT DIETER, WOLF MANFRED, HEINRICH, HANS-WILM, SCHMIDT, DIETER, WOLF, MANFRED
Applicants: HEINRICH HANS WILM, KENNAMETAL INC, SCHMIDT DIETER, WOLF MANFRED, HEINRICH, HANS-WILM, KENNAMETAL INC., SCHMIDT, DIETER, WOLF, MANFRED
Application year: 2000
Main classification: C22C29
IPC codes: C22C29