WO2005023729A1 - Tungsten carbide cutting tool material - Google Patents

Abstract

The disclosed invention describes a new high-performance carbide material, its manufacturing and applications as a cutting tool material for machining ferrous alloys, non-ferrous alloys, metal-matrix-composites, and non-metallic materials. The material is high-purity tungsten carbide material for cutting applications, being essentially free of a metallic binder phase, and comprising an oxygen content of less than 0,5 wt's and a submicron microstructure.

Description

TUNGSTEN CARBIDE CUTTING TOOL MATERIAL

TECHNICAL FIELD

This invention relates to the field of manufacturing and application of polycrystalline tungsten carbide materials suitable for cutting and wear applications.

BACKGROUND ART

Cemented tungsten carbide has become an import material for cutting applications. The cobalt binder phase typically used enables sinterability below 1550 °C and provides good toughness. However, it degrades strength, hardness, chemical stability and temperature resistance compared to pure tungsten carbide. For modern alloys based on Ni, Al, Ti, et cetera, or metal matrix composites cutting tools based on ceramics, diamond or cubic boron nitride have become viable alternatives. Consequently, various attempts have been made to improve relevant properties by reducing the binder content in polycrystalline WC. Ideally, the binder is completely omitted while

- maintaining sufficient toughness.

However, the very high sintering temperatures then required cause excessive grain growth and poor densification resulting in a brittle material with only moderate performance. Surface oxides residing on the particles to be sintered also retard the densification and reduce final

- strength.

The literature suggests a number of routes to manufacture such a dense body. It is then possible to use non-stoichiometric tungsten carbide which exhibits a higher reactivity during sintering and can be consolidated with reasonable effort. However, the non-stoichiometry enhances grain growth during sintering causing said brittleness. In a similar way mixtures of W, WC, carbon, and other carbides and nitrides promote reactive sintering. An unwelcome result is that the content of phases softer than WC increases thus limiting the overall hardness and wear 35. resistance. Additional phases also mean a higher chemical wear with the work piece material, in particular at high temperatures around 700- 1000 °C as observed under modern high-speed machining conditions.

A further approach is to allow for cobalt on an impurity level by milling binderless tungsten 40 carbide with cemented tungsten carbide balls. The latter produce a well distributed contamination of cobalt in the powder. While the cobalt contamination improves the sinterability of the WC powder, grain growth also can become a problem thus reducing the materials fracture toughness. This happens in particular when fine grained or nanosized powders are sintered. Consequently, strength and hardness are below the desirable optimum. In 45 fact, all procedures described to make a "binderless" tungsten carbide contain Co at least on a contamination level which is more than 0.1 % by weight.

All methods utilizing more or less binderless powders or powder mixtures also require pressure during sintering. The most common techniques are hot-pressing and hot isostatic

50 - pressing (HEP). Pressure allows the sintering temperatures to be reduced in order to achieve good densification with little grain growth. HtPing, however, is a complicated process which requires encapsulation of the green compact or powder batch. The encapsulation process usually seals the specimen off which traps undesirable impurities and surface oxides. Detailed analysis of commonly produced "bmderless" tungsten carbide show that always small quantities

55 of residual phases in between the WC grains exist. This can only be overcome by an additional costly reduction treatment. Further manufacturing costs typically increase significantly when higher pressures are required. Conventional hot-pressing or similar techniques like "Rapid Omni-directional Compaction" also do not address the purification need adequately and are commonly slow processes where contaminating impurities can also diffuse from the furnace

60 environment into the specimen.

A need therefore exists to produce a dense high-purity, stoichiometric tungsten carbide material with very fine grain size in order to obtain a very strong, tough and hard body with excellent gh-temperature chemical and mechanical stability and good thermal conductivity. A further need exists for a clean sintering process which is fast, economical, and able to remove surface oxides - in particular when using ultra-fine powders - in an efficient way.

DISCLOSURE OF THE INVENTION

BEST MODE OF THE INVENTION

The disclosed material is an essentially binder free (Co < 0.1%, preferably Co < 0.01% by ^" weight), very pure tungsten carbide (> 99.9% non-oxide purity) with high relative densities (>98.0%) and very fine grain sizes.

The disclosed tungsten carbide has essentially the following features:

- It is made by a process a) that utilizes a high-purity, ultra-fine or nano-sized WC powder batch with essentially no metal additions, b) that utilizes at least a partial in-situ heating, meaning heat is generated within the powder batch, which can be accomplished by passing an electric current through it, by microwaves, or by induction heating. Nonetheless, the powder may be confined in a conductive mold or die which is heated simultaneously with the powder batch, c) which is carried out at reduced oxygen partial pressures, preferably below 10^"2 Pa. d) with very fast heating rates in excess of 100 °C/ min and short dwell times with less than 15 min at maximum temperature, e) with applying a mechanical pressure during sintering. f) with including a powder processing step when admixing toughening agents, comprising of extended ball milling with binder-free WC balls in an organic solvent and a drying step to obtain a granulated powder suitable for dry pressing, or a pressure filtration step utilizing the as- 100 milled (and screened) slurry to produce a solid green compact.

The sintered compact a) has a porosity of equal to or less than 2 %, preferably less than 1%. 105 ^" b) has a mean particle size of equal to or less than 1 μm, but preferably of 0.05 to 0.3 μm. has a Nickers hardness of HVio equal to or better than 23 GPa

110 ^" has a fracture toughness equal to or better than 8 Mpam¹'², but preferably better than 10 Mpam"²

It appears that the combination of the use of an ultra-fine and pure WC powder, in-situ heating with very fast heating rates, vacuum, and with essentially no cobalt, iron or nickel additions

115 results in an extraordinary fine microstructure with grain sizes in the range of 0.01 to 0.5 μm and improved strength, high fracture toughness and hardness, contributing substantially to an overall superior cutting performance which substantially exceeds any reported data on WC- cutting tool. The performance reached is roughly equivalent to a low- to medium-grade polycrystalline cubic boron nitride tool PCBΝ). The in-situ heat generation results in a more

120 _ uniform temperature distribution while allowing for faster heating rates. Also, it enhances decomposition of surface oxides. It is common that during sintering a noticeable amount of material evaporates which is considered indicative for volatiles and surface oxides being removed from powder particle surfaces, thus providing better bonding between particles. The temperature gradient between the hot sintering body and the cold furnace walls supports a

125 purifying outflow and precipitation of volatiles away from the sintering body.

The finer grain structure, in line with higher toughness, hardness and strength, reduces in particular abrasive wear at the contact point between work piece and cutting tool during cutting, but also crater wear caused during machining titanium alloys or other materials which 130 ^~ generate a hot erosive chip during cutting, especially in case of high speed machining. The exceptional performance of the binderless tungsten carbide disclosed has the further advantage that a surface coating is often not needed, though, when coating with CND diamond, the hardness of the cutting edge can be increased while the WC is a better substrate material than commonly used WC-Co tool materials. Binderless WC shows excellent high temperature 135 - strength and by using protective atmosphere during machining higher operation temperatures can be tolerated utilizing the fact that many work piece materials soften at temperatures above 800 °C.

A further advantage of the disclosed material is the broad spectrum of work materials that can 140 be machined, ranging from metals to plastics, metal-matrix composites, some ceramics and rocks and wood products.

Beyond rough and high-speed turning it shows also substantial potential for improved surface finishing.

145 _ The exact conditions required for optimal sintering change somewhat with the specific experimental conditions chosen. Also temperature measurements are usually subject to major measurement errors. Consequently, heating profiles have to be determined experimentally and should be based on monitoring the sintering rate. Typically, heating rates should be fastest up

150 to the point where the maximum densification rate is observed (using constant-heating-rate condition finding runs). Heating rates should subsequently be reduced. Dwell times at maximum temperatures are typically 1 -15 min, depending on the experimental details.

The utilization of powder processing, which is the wet milling with binderless WC balls, and 155 subsequent pressure filtration, or drying plus granulation without organic binder additions, and subsequently dry-pressing results in a more uniform green compact which is less prone to inhomogeneous in-situ heating in the sintering compact. The advantage is a more regular micro structure, thus improving fracture toughness.

160 Yet another important aspect is to use a tungsten carbide powder whose composition is stoichiometric. Stoichiometric powders show less grain growth during sintering than non- stoichiometric powders.

Further, the microstructure - and therefore the toughness - of the WC can be improved by 165 introducing minor quantities of vanadium carbide, chromium carbide, silicon carbide whisker or single-walled carbon nanotubes into the WC powder batch. Additions should be less than 5 vol% - with an optimum between 0.1 and 2 vol% for NC or Cr₂O₃ - and 5-15% for SiC- whiskers. Carbon Nanotubes should be added on a 1- 5 vol% level. VC and Cr₂O₃ act primarily as grain growth inhibitors, thus refining the WC mean grain size. Their particle size 170 _ should be below 0.5 μm, ideally below 0.1 μm. SiC platelets, whiskers or fibers are added in order to further increase the fracture toughness, therefore a particle diameter larger than the mean WC particle size is tolerable but a high aspect ratio desirable. Carbon nanotubes with a diameters around 0.001 μm and a lengths of 1-5 μm appear to have a combined effect of grain size refinement and fracture toughness increase. It is essential to use purified, metal-free single- 175 walled nanotubes with a low contamination of secondary carbon phases.

MODESFORCARRYINGOUT THEINVENTION

180 Example 1:

Sintering:

25 g of an ultra-fine tungsten carbide powder with a specific surface area of 5 m²/g and 99.99% 185 non-oxide purity (OMG America, oxygen content: 0.25 % by weight) was loosely filled into a graphite die (60 mm long, 45 mm outer diameter, 25 mm bore diameter) and enclosed by 2 graphite pistons (40 mm long).

The die set was placed into an experimental hot-press modified in such a way that heating was 190 performed by running an AC current through the water-cooled rams and through the die set. Temperature was feedback controlled by a calibrated pyrometer measuring the center portion of the die surface. The die-set was pre-loaded with 70 MPa uniaxial pressure and twice flushed with argon gas (99.99%) and evacuated down to a final gas pressure of 10^"2 Pa before heat was switched on. A number of evaluation experiments were carried out to find a suitable heating 195 profile. The following profile was subsequently used for making the cutting tool material:

Heating in 10 min from 20 to 1530 °C, heating from 1530 to 1640 °C in 1 min, dwell for 2 min at 1640 °C, shut down power (temperatures were measured on the die surface, being approximately 200 °C lower than internal temperatures).

200 Material evaluation:

Nickers hardness was found to be 24.4 GPa (under 10 kg load), fracture toughness measured from crack lengths 9.2 MPam^1/2 .

205 SEM micrographs were taken of a fractured surface. The average grain size was determined to be of 0.5 μm with a small fraction (less than 2 vol%) in the range of 1 - 10 μm.

Density was measured by the Archimedes method and found to be 98. 9% rel. density

210 Tool bit preparation:

Rectangular tool inserts were prepared from the sintered WC according to ISO specifications. Commercial reference samples of WC-Co and CB were according to CSDPR2525F12, and 215 CRDCR2225F10, respectively.

Turning tests:

Turning tests were carried out on a lathe for high precision machining using the following 220 operational parameters:

Power: 12.5 kW, Rotational Speed: 12.5-1600 rev/min, Typical work piece dimensions: 100 mm diameter, 250 mm length, 15

225 The lathe was capable to maintain a constant cutting speed by continuously adjusting the rotational speed as the diameter of the work piece changed.

Tool holders: T-MAX (manufactured by Sandvik Coromant, Sweden). 230 The time required to produce a flank wear (N_B) of 0.4 mm was chosen as the wear criterion and measured by a microscope with 1 μm optical resolution, mounted on the lathe.

The following work piece materials were used: 235 - 1) Tool steel X12M (manufactured by Dnepropetrovckij Plant, Ukraine). 2) White gray cast iron C412 (manufactured by Krivorozkij Plant, Ukraine), 3) Cast aluminum alloy AL30 (manufactured by Krasnoyarskij Aluminum Plant, Russia). 4) Titanium alloy BT3-1 (manufactured by Zaporozckij Plant of Titanium Alloys, Ukraine), 240 5) Low-carbon Steel 18 XGT (manufactured by Krivorozkij Plant, Ukraine), used for interrupted cutting.

The following cutting tools were tested for comparison:

245 1) WC-Co: BK8 (manufactured by Kirovogradskij Plant of Hard Alloys, Ukraine, containing 8% Co, WC particle size 1-2 μm). 2)Al₂O₃ cutting tool HC1 (manufactured by Nippon Technical Ceramics, Japan) 3) cBN based cutting tool Geksanit-P (manufactued by Poltavskij Diamond Plant, Ukraine, comparable to Amborite). 250 Tool orientations/geometries:

Disclosed WC tool and WC-Co reference tool: cutting edge angle: 45 °, face cutting edge angle: 45°, tool rake angle: 6°, tool cutting edge inclination angle: 0°. 255 Alumina and Geksanit-P tool, as above, but tool rake angle: -6°. The table below shows cutting parameter and the time in minutes required to reach 0.4 mm wear on turning of XI 2M steel and interrupted cutting of 18XGT steel.

260 Cutting speed / 100 100 100 300 300 300 500 500 500 200=* m/min feed rate/ 0.1 0.5 1.0 0.1 0.5 1.0 0.1 0.5 1.0 0.5

265 mm/rev - depth of cut/ 0.5 2.0 4.0 0.5 2.0 4.0 0.5 2.0 4.0 2 mm tool wear time /min

270 WC-Co 12 8 5 - 8 6 3 3 2 0.5 3 disci. WC 30 28 20 25 22 10 20 15 12 25 Alumina 21 15 8 10 8 5 8 5 3 broken cBN • 34 29 22 27 23 11 22 15 13 24

275 *) interrupted cutting, with cooling liquid (3% soda in water)

The WC-Co tool showed a tendency of build-up during rough turning. The character of wear for the disclosed binderless WC is typically abrasive and appears to be more resistant to 280 adhesive wear than WC-Co. For interrupted cutting the disclosed binderless WC tool is still substantially superior to WC-Co, and almost equal with the cBN reference tool.

The table below shows cutting parameters and the time in minutes required to reach 0.4 mm wear for other metals/alloys.

285 Work piece: White grey cast Iron Titanium alloy Aluminum* Al-SiC

290 C412 BT3-1 AL30

Cutting speed /m/min 100 300 500 300 300 150 Feed rate mm rev 0.5 0.5 0.5 0.5 0.5 0.5 Depth of cut 2 2 2 2 2 2

295 Tools wear time /min

WC-Co 45 14

300 disci. WC 25 22 18 30 121 38 Alumina 20 16 10 15 92 12 cBN 28 23 19 33 132 41

"): with cooling liquid, 3% soda solution.

305 The disclosed WC outperformed WC-Co and Alumina under all conditions applied (in terms of wear resistance) thus exhibiting a large versatility in use with respect to work piece materials and cutting conditions. This suggest that the disclosed WC tool is superior to any other common cutting tool material currently available, with the exception of superabrasives. The 310 results further suggest that the disclosed WC tool material is equally suited to turning of other types of MMC, ceramics, plastics, and wood based products.

Various plastics and acrylic glasses were cut for fine finishing under the conditions shown below. The surface finish was measured with a profilometer (Profilograph 209). 315

320 Cutting tools

WC-Co (BK8) disclosed WC

325 Cutting speed/ m/min 300 300 Feed rate / mm/rev 0.1 0.1 Depth of cut /mm 0.1 0.1

Work piece materials Surface roughness / Ra

Getinaks: 1.5 0.8 Steklotekstolit: 2.0 1.25 Stekloplastik: 2.5 1.0

335

For all the three plastic materials, the disclosed WC is significantly more effective in obtaining a good surface finish than the WC-Co tool.

340 Example 2: Comparison with low-grade PCBN tool

A tungsten carbide tool manufactured and prepared as described in Example 1 was tested against a Valenite VC730 PCBN cutting tool. The latter is made from a PCBN material 345 containing approximately 50 vol% of ultrahard cBN grains (which is less than in Geksanit-P or Amborite). Testing equipment, tool geometry and cutting angles were the same as in Example 1. Tests were carried out on heat treated steel and grey cast iron, with results shown in the table below.

350 Common conditions: Feed rate: 0.1 mm/rev, depth of cut: 0.5 mm. Shown is the time to reach a wear of 0.4 mm. Coolant used as in Example 1. work material cutting speed wear time / disci. WC wear time/ NC730 m/min min min

355 Steel 40XHRC50 80 59 63 (0.4%C, 1% Cr) heat treated

360 Grey Cast Iron 120 73 68 HB230-250 - (2.4%C, 3%Cr)

365 The results show that the disclosed carbide is superior in machining grey cast iron where wear is typically more abrasive than with steel, while (in particular low-carbon) steel tends to have more chemical interaction with the tool materials, also causing higher cutting forces.

370 Example 3: Cutting tool from microwave sintered WC

60 g of the tungsten carbide powder was milled with 90 g cobalt-free tungsten carbide balls (average diameter: 4 mm) in n-hexane for ca. 170 hrs on a roller bar mill. 3 ml of the slurry- was filled into a die set for pressure filtration and consolidated for ca. 20 min into a solid tablet 375 of 20 mm under a constant pressure of 5 MPa. The tablet was dried at ambient conditions for 3 hrs and then for another 2 hrs at 400 °C in a vacuum furnace (10^"3 Pa).

A laboratory-type microwave furnace operating at 2.45 GHz (single mode) was available with a programmable, continuous wave power output up to 1100 W. The furnace was 380 equipped with a tunable microwave cavity containing a specimen compartment suitable for operation under controlled atmosphere and reduced pressures. The specimen was placed in a porous zirconia crucible (ca. 80-85% porosity) which was covered with a zirconia lid. The zirconia lid contained a 4 mm hole for monitoring the temperature by a 2-color pyrometer through an optical port. The specimen compartment was evacuated to a pressure of ca. 10^"3Pa. 25

385 After a set of condition finding runs sintering was carried out by ramping the temperature within 5 min to 1940 °C, with subsequent dwelling for 5 min. A maximum relative density of 98.9 % was measured by the Archimedes method. This specimen was processed into a tool insert and characterized as detailed in Example 1 and tested under the conditions stated below.

390 Cutting angles were chosen as in Example 1.

- Work piece material: X12M steel, cutting speed: 300 m/min, feed rate: 0.5 mm/rev, depth of cut: 2 mm.

395 Tool properties:

Average grain size: 0.4 μm hardness: 24.4 +/- 0.4 GPa fracture toughness : 9.6 +/- 0.6 MPam^{1 2} wear time (0.4 mm): 24 min

400 The wear behavior and cutting performance improved noticeably compared to similar conditions in Example 1. This is attributed to the somewhat finer grain size. The micro structure showed less coarsening, which is attributed to the wet powder processing and the more pronounced in-situ heating of the specimen.

405 Example 4: Cutting tool from nanosized WC

An ultrafme grained fraction of WC with a particle size of approximately 80 nm was produced from the powder used in Example 1 by dispersing and separating large particles from fines by sedimentation. The re-concentrated dispersion of nano-particles was pressure filtrated to 410 produce a green compact for sintering.

For comparison, another set of specimens (referred to as "reference specimens") was processed into green compacts as detailed in Example 3.

415 Sintering was further carried out in the modified hot-press with electric current heating as described in Example 1, but using a graphite die set with (TD: 20 mm, OD: 40 mm, length: 60 mm). Conditions were the same as in example 1, but with constant heating rates of 200 °C/min up to maximum temperature (see table below). The reference specimens and nanosized specimens were used to determine adequate conditions for sintering. A subset of the reference 420 specimens was produced under conditions which can be described as overheated to promote more grain growth. This served as a comparative basis for commonly available binderless WC materials which usually show grain sizes above 2 μm.

Characterization was carried out as outlined above and turning tests were carried out with tool 425 inserts made according to Example 1 on X12M steel with cutting speed 200m/s, feed rate 0.32 mm/s and depth of cut 0.2 mm.

Specimen: Reference 1 Reference 2 Reference 3 Nano 1 WC-Co (BK8)

430 Parameter

Max. Sintering 1630 1750 1800 1590 Temperature/ °C Dwell time/ min 1 20 20 1

435 Relative density /% 98.7 99.1 99.8 97.2* mean grain size/μm 0.5 2.1 5.5 0.1 Nickers hardness 24.3 20.3 8.4 26.4

440 Fracture toughness 9.1 8.2 7.6 10.9 MPam^{1 2}

Wear time / min 91 57 40 146

445 *): The absolute density of nanosized materials tends to be lower than for coarse due to the large amount of grain boundary atoms. Porosity here is likely less than 2.8 %.

The micro structure refinement shows a tremendous improvement of mechanical properties and wear resistance over micron and submicron particle sizes. On the nano-level the wear behavior 450 of the disclosed WC becomes comparable with superabrasives.

Example 5: Grain size refinement by using grain growth inhibitors

Using the powder processing procedure for producing a green compact as described in 455 Example 3, 2 vol % of a nanosized Cr₂C₃ (mean grain size 80nm as determined by X-ray techniques and scanning electron microscopy) was added as a grain growth inhibitor and sintered as under the conditions described in Example 3 (for maximum temperature see table below). A second specimen was produced in the same way but containing nanosized NC (60 nm mean particle size, as determined by X-ray techniques and scanning electron microscopy). 460 A third specimen was produced with a volume fraction of 5% opened, purified and dispersed, single-walled carbon nano-tubes (average length: 2 μm)

- Hardness and toughness measurements, grain size and micro structure evaluation, and wear tests (on X12M steel) were carried out as stated in Example 1.

*tUJ Specimen: Specimen from Cr₂C₃ NC nano-tubes Example 1/ for - comparison

470 Sintering temperature/°C 1640 1640 1640 1690 Dwell time / min 2 2 2 2 Relative density 98.9 98.6 98.6 98.5 Mean WC grain size/μm 0.5 0.35 0.35 0.4 Nickers Hardness 24.4 24.6 24.7 23.8

475 HN,o / GPa

Fracture toughness/MPam 9.2 9.8 9.7 11.6

Wear time / min 22 23 23 24

480 The results show that the addition of nano-sized additives effectively reduces the WC grain size and also promotes a somewhat better cutting performance. Some of the carbon tubes had decomposed into nanosized graphite platelets. In particular the remaining nanotubes are believed to have a toughening effect due to their needle-shape. The improved fracture 485 toughness and finer grain size may compensate for an assumed loss in strength due to weaker NC-, Cr₂C₃- or carbon- WC grain boundaries.

^~ Example 6: Matrix reinforcement

490 Using the powder processing method described in Example 3 10 vol% of SiC whiskers (diameter: 0.1 - 3 μm and length: 5 - 100 μm a green compact was sintered in the modified hot-press by electric current, and with a maximum uniaxial pressure of 85 MPa. Heating rate until 1600 °C was 200 °C/min, from there to 1700 °C 50 °C/min, with a 3 min dwell time before shutting power off. The tool, as prepared according to the specification given in

495 Example 1, was tested under the conditions given in Example 2, using Steel 40XHRC50 as the work material.

Tool properties:

500 Rel. Density: 98.1 % Mean matrix grain size: 0.7 +/- 0.1 μm Hardness: 22.8 +/- 0.5 GPa Fracture toughness: 10.1 +/- 0.4 MPam^{1 2} wear time (0.4 mm wear): 58 min.

505 Conditions of the sintering process were not optimized. Applying a condition finding procedure as described previously is likely to further improve density and cutting tool performance.

Claims

CLAIMS:

We claim: 1. A sintered, dense, high-purity tungsten carbide material for cutting appHcations, being essentially free of a metallic binder phase, and comprising an oxygen content of less than 0.5 wt% and a submicron microstructure.

2.The cutting tool material of claim 1 made by a sintering procedure comprising the steps of: a) providing a very fine, high-purity tungsten carbide powder; and b) avoiding any contamination with nickel, cobalt, iron of said tungsten carbide powder during any manipulation or powder processing prior to, or during, sintering; and c) providing a vacuum, or an inert or reducing atmosphere during the sintering process, thus allowing for evaporation and decomposition of WC particle surface oxides during the sintering process, and d) applying an external mechanical pressure to said tungsten carbide powder batch being sintered, and e) consolidating and bonding said tungsten carbide powder batch being sintered into a strong body by applying heat generated by f) an electric current passing through said tungsten carbide powder batch, or microwaves with a frequency of 2 to 25 GHz, or induction within said powder batch, wherein at least a significant part of the heat is generated within said tungsten carbide powder batch, providing a maximum temperature therein in the range of 1500 to 2200 °C.

3. The cutting tool material of claim 1 made by a sintering process with a) providing a stoichiometric tungsten carbide powder with a specific surface area of 1 to 20 m²/g, a non-oxide purity of or better than 99 wt%, and an oxygen content of 0.5 wt% or less, and b) establishing an oxygen partial pressure of the sintering atmosphere between 1 and 10^"10 Pa, and c) applying a maximum mechanical pressure of 30 to 500 MPa, and d) applying a maximum heating rate of 50 to 2000 °C/min.

4. The cutting tool material of claim 1 made by a sintering process with preferably a) providing a stoichiometric tungsten carbide powder with a specific surface area of 5 to 20 m²/g, a non-oxide purity of or better than 99 wt%, and an oxygen content of 0.5 wt% or less, and b) establishing an oxygen partial pressure of the sintering atmosphere of 0.01 and 10^'10 Pa, and c) appyling a maximum mechanical pressure of 50 to 200 Mpa. d) applying a maximum heating rate of 100 to 700 °C/min.

5. The cutting tool material of claim 1, wherein an atmosphere contaimng 1 to 20 vol% hydrogen is provided to the sintering procedure, with the remaining being argon, helium, or any other oxygen- free inert gas.

6. The cutting tool material of claiml, wherein the sintering process is carried out within an electrically conductive die set which is simultaneously heated by said electric current, induction or microwaves.

7. The cutting tool material of claim 2, wherein said electric current is pulsed at a frequency of 50 to 1 MHz, but preferably at a frequency of 0.1 to 20 kHz.

8. The cutting tool material of claim 1 comprising a) a mean tungsten carbide particle size of 0.05 to 1 μm, and b) a relative density of equal to or better than 98%, and c) an impurity content of less than 0.2 wt % by weight except chromium carbide (Cr₂C₃), vanadium carbide (NC), silicon carbide (SiC) and carbon modifications.

9. The cutting tool material of claim 8, wherein a volume fraction of less than 5 percent of said tungsten carbide exceeds 2 μm in grain size.

10. The cutting tool material of claim 1, wherein the content of iron, cobalt or nickel is less than 0.01 wt%.

11. The cutting tool material of claiml, wherein said cutting tool material contains 0.1 to 15vol% Cr₂C₃ ,SiC, VC, carbon modifications or mixtures thereof as growth inhibitors and toughening agents.

12. The cutting tool material of claim 11 preferably containing 0.1 to to 5 vol% Cr₂C₃ or VC, with a mean particle size between 0.001 and 0.5 μm.

13. The cutting tool of claim 11 preferably containing 2 to 15 vol% SiC with a mean a mean particle width or thickness between 0.01 and 5 μm and an aspect ratio of 1 to 100.

14. The cutting tool of claim 11 preferably containing purified carbon nanotubes with a mean particle width or thickness of 0.001 to 0.01 μm and an aspect ratio between 50 and 10000.

100 15. The cutting tool material of claim 1, wherein said material possesses a a) Vickers Hardness HVio equal to or better than 23 GPa; and b) a fracture toughness k_rc equal to or better than 8 MPam^1/2. 105

16. The cutting tool material of claim 1 being used to machine iron based alloys, and preferably grey cast iron.

17. The cutting tool material of claim 1 being used to machine aluminum based alloys or aluminides, 110 magnesium alloys, titanium based alloys or nickel based alloys.

18. The cutting tool material of claim 1 being used to machine glasses, glass ceramics, oxide ceramics, or graphite.

115 19. The cutting tool material of claim 1 being used to machine metal-matrix composites.

20. The cutting tool material of claim 19, wherein the metal-matrix-composites being machined contain one or more different ceramic phases, or carbon reinforcements.

120 21. The cutting tool material of claim 19 wherein the metal-matrix-composites contain alloys based on Fe, Ni, Ti, Si, Mg or Al.

22. The cutting tool material of claim 1 being used to machine monolithic plastics, fiber reinforced plastics, or plastics with inorganic fillers.

125 23. The cutting tool material of claim 1 being used to machine wood or wood based products.