Hard sintered body

Abstract

The present invention provides a sintered body containing W and WC, having excellent hardness, strength, compactness, and corrosion resistance, without containing W.sub.2C, and capable of being used for the purpose of a cutting tool or a glass molding die, or a seal ring. There is provided a sintered body containing 4 to 50 vol % of tungsten metal as binder phases, 50 to 95 vol % of tungsten carbide (WC), and 0.5 to 5.0 vol % of tungsten oxide (WO.sub.2), in which the tungsten oxide (WO.sub.2) has an average grain size of 5 nm to 150 nm and is present in a sintered body structure at an average density of 5 to 20 particles/μm.sup.2.

Claims

1. A sintered body comprising: 4 to 50 vol % of tungsten metal as binder phase; 50 to 95 vol % of tungsten carbide (WC); and 0.5 to 5.0 vol % of tungsten oxide (WO.sub.2), wherein the tungsten oxide (WO.sub.2) has an average grain size of 5 nm to 150 nm and is present in a sintered body structure at an average density of 5 to 20 particles/μm.sup.2, and the tungsten oxide (WO.sub.2) is dispersed in the sintered body structure.

2. The sintered body according to claim 1, wherein the sintered body structure does not contain W.sub.2C.

3. The sintered body according to claim 1, wherein a fracture toughness value of the sintered body is 6.7 MPa.Math.m.sup.1/2 or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a W—WC state view, and shows that W.sub.2C having low strength is generated, in a case where carbon is contained, in a temperature range of 1400° C. to 1450° C. The horizontal axis is atom % of carbon.

(2) FIG. 2 shows a measurement result of XRD regarding a sintered body containing W—WC—WO.sub.2 according to the invention.

(3) FIG. 3 shows an example of an image of a WO.sub.2 portion confirmed based on a scanning electron microscope image (magnification: 10000 times) obtained by observing the cross section structure and a mapping image of a W element, a C element, and an O element using an EDX subjected to binarization processing, regarding the sintered body containing W—WC—WO.sub.2 of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Next, a sintered body of the invention will be described in detail with reference to examples.

Examples

(5) As a raw material powder, WC powder having a predetermined average grain size and W fine powder having a surface, to which oxygen is applied, were prepared (sample no. 1 to 8 of Table 3), these raw material fine powders were blended and mixed to have a predetermined composition, the sintering was performed using the raw material mixed powder sintered under the conditions shown in Table 3, and accordingly, the present invention sintered bodies 1 to 8 were produced.

(6) For comparison, by performing the sintering with respect to the raw material powder (sample no. 12 of Table 3) having a blending composition beyond the present invention range shown in Table 3, a comparative example sintered body 12 was produced.

(7) For comparison, in the same manner, by performing the sintering with respect to the raw material powder (sample no. 11 and 13 of Table 3) which satisfies the blending composition of the present invention range shown in Table 3, but in which oxygen was applied under the conditions beyond the present invention range (100° C. to 1300° C.), and the raw material powder (sample no. 14 of Table 3), in which the oxygen was not applied, comparative example sintered bodies 11, 13, and 14 were produced.

(8) For comparison, in the same manner, by performing the sintering with respect to the raw material powder (sample no. 15 of Table 3) having the blending composition of the present invention range shown in Table 3 at the sintering temperature beyond the present invention range, a comparative example sintered body 15 was produced.

(9) Regarding the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 15 obtained as described above, the cross section structure thereof was observed with an SEM (magnification: 10000 times), an average crystal grain size of crystal grains of W, WC, and WO.sub.2 configuring the sintered body obtained by the image processing and the number per unit area of WO.sub.2 are shown in Table 4.

(10) In the same manner, regarding the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 15, a density and a fracture toughness value were also measured and shown in Table 4.

(11) In addition, regarding the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 15, the presence or absence of W.sub.2C was confirmed by XRD measurement, and the presence amount is shown in Table 4 as a ratio of peak strength of (101) plane of W.sub.2C with respect to peak strength of (110) plane of W.

(12) FIG. 2 shows an XRD chart measured regarding the present invention sintered body 3, but a peak of W.sub.2C could not be confirmed. In addition, FIG. 3 shows a scanning electron microscope image (magnification: 10000 times), observed regarding the cross section of the present invention sintered body 3.

(13) The present invention sintered bodies 1 to 8 have fine organization structure in which all of average crystal grain sizes of crystal grain of W configuring the sintered body is small as 600 nm or less.

(14) The present invention sintered bodies 1 to 8 have a high density, and according to the XRD measurement, the presence of W.sub.2C causing a decrease in strength could not be confirmed regarding the present invention sintered bodies other than the present invention sintered body 3.

(15) In the present invention sintered bodies 1 to 8, a predetermined volume amount of the WO.sub.2 particles dispersed in the structure was satisfied, and the average density of particles having a predetermined average grain size is also satisfied.

(16) Even in a fracture toughness test, a high fracture toughness value was shown.

(17) On the other hand, the comparative example sintered body 12 having the blending composition beyond the present invention range has the same sintering conditions as those of the present invention sintered body, but the density is deteriorated. In addition, the comparative example sintered body 15 under the sintering conditions beyond the present invention range was subjected to the high temperature sintering, and accordingly, generation of W.sub.2C is observed in the XRD measurement, and a predetermined fracture toughness value was not satisfied.

(18) In the comparative example sintered bodies 11, 13, and 14, the raw material powder in which oxygen was applied under conditions beyond the present invention range (100° C. to 1300° C.) was used, and accordingly, the fracture toughness value was not satisfied.

(19) Next, each cutting tool was produced by grinding process from the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 15, a TiCN and Al.sub.2O.sub.3 layer was coated on the surface thereof by a CVD method, and a coating tool using present invention sintered body tools 1 to 8 and comparative example sintered body tools 11 to 15 was produced, and a high-speed feeding cutting process test was performed under cutting conditions shown below.

(20) Work material: S45C

(21) Cutting speed: 200 m/min

(22) Depth: 1.0 mm

(23) Feed: 0.7 mm

(24) The cutting process test was performed up to the maximum cutting time of 180 seconds, and a blade edge was confirmed for every cutting time of 15 seconds. The test result is shown in Table 4.

(25) From the result shown in Table 4, in the present invention sintered body tools 1 to 8, a dramatically long life was shown under the severe cutting conditions of high speed and high depth, and the present invention sintered body tools showed particularly excellent properties as a cutting tool in which a temperature of a blade edge easily becomes a high temperature.

(26) In contrast, in the comparative example sintered body tools 11 to 15, the tool life time was short and fractures of the blade edge occurred.

(27) TABLE-US-00003 TABLE 3 Blending Average grain Preprocessing condition of W Sintering conditions composition size Holding Sintering Holding Sample (mass %) (nm) Temperature time temperature time Pressure no. W WC W WC Oxygenation (° C.) (min) (° C.) (min) (MPa) Atmosphere Present 1 6.1 93.9 5 600 Performed 200 30 1200 5 5500 Atmosphere invention 2 55.2 44.8 25 6800 Performed 1300   5 1200 5 5500 N.sub.2 sintered 3 23.5 76.5 25 550 Performed 100 30 1200 5 4500 N.sub.2 body 4 34.6 65.4 30 30 Performed 600 30 1200 5 4500 Atmosphere 5 45.1 54.9 80 60 Performed 200 30 1200 5 4500 Atmosphere 6 17.9 82.1 140 650 Performed 1000  30 1200 5 5500 Atmosphere 7 34.5 65.5 5 15 Performed 600 30 1200 5 50 Vacuum 8 21.3 78.7 40 8800 Performed 200 30 1200 5 4500 N.sub.2 Comparative 11 23.5 76.5 25 600 Performed *No temperature process 1200 5 4500 Atmosphere example 12 *1.3 *98.7 5 600 Performed 700 30 1200 5 4500 Atmosphere sintered 13 23.5 76.5 30 500 Performed *50 *5 1200 5 4500 Atmosphere body 14 23.5 76.5 30 500 *None 1200 5 4500 N.sub.2 15 23.5 76.5 30 500 Performed 200 30 *1600  5 4500 Atmosphere Note) *indicates that the condition of the invention is not satisfied.

(28) TABLE-US-00004 TABLE 4 WO.sub.2 Sintered body properties Tool Volume amount of each Average Presence or Fracture properties component after sintering Average crystal grain size density absence of toughness Tool life time Sample W WC WO.sub.2 W WC WO.sub.2 (particles/ Density XRD WO.sub.2 value (after 180 no. (vol %) (vol %) (vol %) (nm) (nm) (nm) μm.sup.2) (g/cm.sup.3) peak (MPa .Math. m.sup.1/2) seconds) Present 1 4 95 1 10 650 5 7 14.6 Present 6.9 No fracture invention 2 45 50 4 173 6890 50 11 16.2 Present 6.8 No fracture sintered 3 15.5 80 4.5 181 623 130 17 15.3 Present 7.2 No fracture body 4 27.5 70 2.5 190 35 105 6 15.7 Present 7.0 No fracture 5 35 60 5 293 68 150 20 15.8 Present 6.8 No fracture 6 14.5 85 0.5 600 810 85 5 15.0 Present 6.7 No fracture 7 26 70 4 10 20 20 10 15.4 Present 7.0 No fracture 8 15 82 3 210 8950 70 14 15.2 Present 6.8 No fracture Comparative 11 5 80 *15 183 656 *350 8 14.9 Present 5.2 *Fracture at 30 example seconds sintered 12 *0 *99  1 6 663 *2 *0.5 14.3 Present 4.7 *Fracture at 15 body seconds 13 15 80 5 176 610 120 *25 15.2 Present 5.3 *Fracture at 30 seconds 14 19.9 80 *<0.1 183 617 *3 *0.02 15.7 *Absent 6.1 *Fracture at 90 seconds 15 *0 80 *<0.1 None Not *2 *0.01 15.8 *Absent 5.0 *Fracture at 15 measurable (W.sub.2C peak) seconds Note) *indicates that the condition of the invention is not satisfied. Note) **is comparative example showing an example where WC and W.sub.2C are precipitated, but it is difficult to measure both elements separately, and therefore, the measurement cannot be performed.

INDUSTRIAL APPLICABILITY

(29) The sintered body according to the invention has excellent compactness and excellent fracture toughness, and can be used as a blade edge material of a cutting tool or a wear-resistant tool material such as a mold used at a high temperature, and is extremely useful.