FR2686873A1 - Heat-resistant sintered hard alloy - Google Patents

Abstract

This alloy includes 35 % to 95 % by weight of a complex boride of the WCoB type in a cobalt-based alloy and includes 1.5 % to 4.1 % of boron, 19.1 to 69.7 % of tungsten, optionally 1 to 25 % of chromium, the remainder consisting of cobalt and of a maximum quantity of 1 % of impurities; it being possible for nickel, iron and/or copper to replace a certain quantity of the cobalt. Application: production of an alloy exhibiting improved properties at low temperature and high temperature.

Description

 The present invention relates to a hard heat-sintered hard alloy consisting of a hard phase consisting mainly of a complex boride of the WCoB type, and of a cobalt-based alloy phase forming a hard phase-binding matrix. a hard alloy which exhibits excellent room temperature characteristics as well as excellent high temperature characteristics, such as strength and high temperature oxidation resistance, and also serves as a hot extrusion die for copper rod.

 The requirements for wear-resistant sintered hard materials have become increasingly stringent and the industry is looking for improved materials with wear resistance and resistance to heat, corrosion resistance, etc. .

 As sintered hard materials, carbides, nitrides and carbonitrides, such as WC based hard alloys and TiCN type cermets, are well known.

As substitutes for the aforementioned hard materials, hard alloys and cermets comprising metal borides such as WB and TiB 2, as well as complex metal borides such as Mo 2 Fe 2 Bi 2 Ni 2 Bi 2 Ni 2 have recently been proposed with regard to the excellent properties of borides such as Extreme hardness, high melting point and high electrical conductivity. In addition, stellites are used as wear-resistant cobalt-based materials.

 A hard alloy formed by bonding WB to a nickel-based alloy, such as that described in Japanese Patent Nos. Sho 56-45985, n Sho 56-45986 and n Sho 56-45987, is a wear-resistant paramagnetic material. intended to be used especially in watch cases and jewelry, and is not intended to produce structural materials to be used at high temperatures.

 Ceramic materials comprising metal borides such as TiB 2, described in Japanese patents published under the numbers Sho 61-50909 and n Sho 63-5353, exhibit extreme hardness and heat resistance, but give poor resistance to thermal shocks due to the absence in these materials of a metallic bonding phase forming a matrix.

 In general, hard materials formed by adding metals to metal borides have the disadvantage of tending to form a fragile third phase and make it difficult to obtain a high mechanical strength or toughness.

 Hard alloys comprising metal complex borides such as Mo2FeB2 and Mo2NiB2 formed by reaction during sintering have been developed to overcome the aforementioned drawback.

 A hard alloy of the Mo2FeB2 type described in Japanese Patent Publication No. Sho 60-57499 exhibits excellent mechanical properties, wear resistance, and corrosion resistance at room temperature, but strength and resistance to abrasion. unsatisfactory high temperature oxidation due to its iron-based bonding phase forming a matrix.

A hard alloy of the Mo2NiB2 type described in Japanese Patent Application Laid-open No.
Sho 62-196353 exhibits excellent high temperature and corrosion resistance properties, but has poor wear resistance and non-stick properties, since the Mo2NiB2 complex boride has a micro hardness.
Vickers of about 15 GPa and thus is not hard enough, and its bonding phase consists of a nickel-based alloy. Stellites have excellent high temperature properties, but their hardness is too low for use in wear resistant materials.

 An object of the present invention is to provide a sintered hard alloy having excellent properties at room temperature, as well as very good high temperature properties, such as strength and resistance to oxidation at high temperature.

According to the present invention, there is provided a heat resistant sintered hard alloy comprising 35 to 95% by weight of a complex boride of the type
WCoB and a cobalt-based alloy phase forming a matrix. The hard alloy may comprise 1.5 to 4.1 wt% boron, 19.1 to 69.7 wt% tungsten, the remainder cobalt and unavoidable impurities. In addition to the aforementioned elements, the hard alloy may contain 1 to 25% by weight of chromium to improve the mechanical properties and the corrosion resistance. In addition, the hard alloy may comprise 1.5 to 4.1% by weight of boron, 19.1 to 69.7% by weight of tungsten, 1 to 25% by weight of chromium, and at least one element selected from nickel, iron and copper. Nickel, when present, replaces cobalt in an amount of 0.2 to 30% by weight, based on the amount of cobalt.

Iron, when present, replaces cobalt in an amount of 0.2 to 15% by weight, based on the amount of cobalt. Copper, when present, replaces cobalt in an amount of 0.1 to 7.5 wt.%, Based on the amount of cobalt. The rest of this alloy consists of cobalt and unavoidable impurities.

 In this specification, WCoB and a complex boride identified as consisting of X-ray diffraction WCoB, comprising tungsten and cobalt, wherein part of the tungsten may be replaced by chromium and part of the cobalt may be replaced by chromium, nickel, iron or copper are referred to as the complex boro of the WCoB type.

 The complex boride of the WCoB type has the following advantages. The formation of a fragile third phase, which tends to form in a boride hard alloy, can be suppressed by formation of the WCoB-type complex boride by reaction during sintering. The micro-Vickers hardness of the WCoB type boride is greater than 30 GPa and greater than that of other complex metal borides such as Mo2FeB2 and Mo2NiB2, and is the same as or better than carbides and nitrides which are commonly used for materials. hard. In addition, the WCoB-type complex boride exhibits excellent resistance to oxidation.

 In the case where the content of complex boride of the WCoB type is less than 35% by weight, the wear resistance of the hard alloy is reduced due to the insufficient amount of the complex boride and said hard alloy is likely to undergo high deformation at high temperature due to the insufficient development of complex boride networks in the cobalt-based alloy phase as a matrix. On the other hand, in the case where the content of complex boride of the WCoB type is greater than 95% by weight, the mechanical strength of the hard alloy is greatly reduced, although its hardness is increased. For the above reason, it is preferable that the content of the WCoB type complex boride is in the range of 35 to 95% by weight.

 Boron is an essential element for the formation of the WCoB-type complex boride in the heat resistant sintered hard alloy. With a boron content of less than 1.5% by weight, the complex boride is present in an amount of less than 35% by weight and, with an amount of boron of greater than 4.1% by weight, the complex boride is present in a amount greater than 95% by weight, which causes a sharp reduction in the strength of the hard alloy. For the above reason, it is preferred that the amount of boron in the hard alloy be in the range of 1.5 to 4.1 wt.

 Tungsten is also an essential element for the formation of the complex boride of the WCoB type.

The stoichiometric ratio in the complex boride of the type
WCoB is chosen so that the ratio W: Co: B is equal to 1: 1: 1. However, it is not necessary that the WCoB type complex boride, which is useful in practice, be a perfectly stoichiometric compound, this compound may have a composition variation equal to a few percent. Accordingly, it is not necessary that the W / B molecular ratio (hereinafter referred to as the W / B ratio) be 1, but it is important that the W / B ratio be within a range of specific including the value 1 as an approximate center.

 The test results indicate that, in the case where the W / B ratio is much lower than 1, cobalt borides such as Co2B are formed and, in the case where the W / B ratio is much greater than 1, intermetallic compounds of tungsten and cobalt such as W6Co7 are formed, which causes a reduction in the mechanical strength of the hard alloy in either case.

 When the W / B ratio is in the range of 0.75 to 0.135 x (11.5 - X), X denotes the boron content as a percentage by weight, even if the third phase mentioned above is formed, the third phase has little effect on the mechanical strength of the hard alloy, which means that there is an acceptable decrease in mechanical strength.

 In the case where the W / B ratio is greater than 1, a portion of the excess tungsten forms a solid solute in the cobalt-based alloy phase forming the matrix, which strengthens the matrix-forming phase, thereby improving the properties sintered hard heat resistant alloys. However, since the amount of the cobalt-based alloy phase forming the matrix decreases with the increase in the amount of the WCoB-type complex boride, it is necessary to reduce the amount of said excess tungsten in the matrix-forming phase together. with the aforementioned increase, so as to maintain the mechanical strength of the hard alloy.

 For the above reason, it is preferable that the upper limit of the amount of tungsten corresponds to a W / B ratio equal to 1.35 in the case where the amount of boron is the lowest (1.5% by weight), and at a W / B ratio of 1 in the case where the amount of boron is the highest (4.1% by weight). This range is represented by the formula 0.135 x (11.5 - X), wherein X is the weight percent of boron.

 Therefore, it is desirable that the amount of tungsten in the hard alloy corresponds to a W / B ratio in the range of 0.75 to 0.135 x (11.5 - X), preferably in the range of 0.8 to 0.135 x (11.5 - X), i.e., in the range of 19.1 to 69.7% by weight, preferably 20.4 to 69.7% by weight. weight, in said hard alloy.

 In the case of a sintered hard alloy containing chromium, it is presumed that the chromium forms a solid solute in the complex boride of the WCoB type and forms a multiple boride (WxCoyCrz) B of the complex boride of the WCoB type, in which the cobalt , rather than tungsten, is partially replaced by chromium and the sum x + y + z is equal to 2 and, in addition, chromium also forms a solid solute in the cobalt-based alloy matrix, so that the corrosion, heat and oxidation resistances of the sintered hard alloy are improved.

 In addition, chromium refines the multiple boride phase (WxCoyCrz) B and improves the mechanical properties of the sintered hard alloy. With a chromium content of less than 1% by weight, the abovementioned improvement can not be obtained and, with a chromium content greater than 25% by weight, the mechanical properties of the sintered hard alloy are greatly reduced because of the formation of a fragile phase such as a CoCr phase sigma (a). Accordingly, it is preferred that the chromium content be in the range of 1 to 25% by weight.

 In the case of a sintered hard alloy containing nickel, it is assumed that nickel replaces cobalt and forms a solid solute in the cobalt-based alloy phase constituting the matrix, and improves the mechanical properties, the resistance to corrosion and heat resistance of the hard alloy. With nickel replacement to a content of less than 0.2% by weight of the amount of cobalt, the aforementioned improvements in mechanical properties and other properties can not be obtained and, with replacement with nickel in a higher grade. at 30% by weight of the amount of cobalt, the abrasion resistance is reduced due to the decrease in hardness. Accordingly, it is preferred that the amount of nickel, replacing cobalt, be in the range of 0.2 to 30% by weight of the amount of cobalt.

 Iron mainly replaces cobalt in the WCoB-type complex boride and the cobalt-based alloy phase forming the matrix, and improves the temperature-based strength. With a replacement by iron in a content of less than 0.2% by weight of the amount of cobalt, the above improvement is not obtained and, with a replacement by iron in a content greater than 15% by weight of the amount of cobalt, the hard alloy becomes less resistant to corrosion, heat and oxidation. Accordingly, in the case of the sintered hard alloy containing iron, it is preferable that the iron replace the cobalt in a content of 0.2 to 15% by weight of the amount of cobalt.

 Copper replaces cobalt and forms a solid solute in the cobalt-based alloy phase forming the matrix, and improves the corrosion resistance and thermal conductivity of the sintered hard alloy. With replacement by copper in a content of less than 0.1% by weight of the amount of cobalt, the above improvements are not obtained and, with a replacement by copper in a content greater than 7.5% by weight of the amount of cobalt, the mechanical properties and the heat resistance are reduced. Accordingly, it is preferred that the copper replaces the cobalt to a content in the range of 0.1 to 7.5 wt.% Of the amount of cobalt when copper is added to the hard sintered alloy.

 The unavoidable impurities present in the sintered hard alloy consist mainly of silicon, aluminum, manganese, magnesium, phosphorus, sulfur, nitrogen, oxygen, carbon, etc., and it is desirable that the amount of these elements present as impurities is as low as possible. However, in the case where the total amount of these elements present as impurities is less than 1.0% by weight, the detrimental effects of these elements on the properties of the hard sintered alloy are relatively small.

Accordingly, it is preferred that the total amount of unavoidable impurities is less than 1.0% by weight, preferably less than 0.5% by weight.

 In the case where the sintered hard alloy is used for a wear-resistant coating in which the mechanical strength is not critical, and silicon and aluminum or the like are intentionally added so as to improve the resistance to oxidation of the coating, the total amount of the aforementioned elements may be greater than 1.0% by weight.

 The hard sintered alloy is produced by blending powders of tungsten, cobalt, chromium, nickel and iron borides; boron alloy powders with at least one element selected from tungsten, cobalt, chromium, nickel, iron and copper; or boron powder and metal powders selected from tungsten, cobalt, chromium, nickel, iron and copper, or alloy powders containing at least two of these metal elements, then by grinding in medium moistening of the mixture with an organic solvent by means of a vibrating ball mill or the like, drying, granulating and shaping, followed by liquid-phase sintering of the green compact material in a non-oxidizing atmosphere, for example under empty, in a reducing gas or in an inert gas.

The hard phase, i.e. the complex boro of the WCoB type of the sintered hard alloy, is formed by reaction during sintering. A mixture of powders obtained by mixing metal powders such as cobalt, chromium and nickel powders to form the alloy-based phase.
As matrix, with the complex boride of the WCoB type, such as WCoB and (WxCoyCrz) B are prepared by reaction of tungsten boride, cobalt boride, a boron powder with metal powders such as powders tungsten, cobalt and chromium, etc., beforehand in an oven, can also be used as raw material powders.

 Sintering in the liquid phase is usually conducted in the temperature range of 1100 to 1400 C and for a time of 5 to 90 minutes depending on the composition of the hard alloy. A hot pressing method, a hot isostatic pressing method, a sintering method using an electrical resistor or the like may also be used.

EXAMPLES
The powders of compounds listed in Table 1 and the metal powders listed in Table 2 were blended to give the compositions shown in Table 1.
Table 3, the mixing ratios being presented on the
Table 5. The mixed powders were subjected to wet milling with acetone using a ball mill for 28 hours, then dried and granulated. The powders thus obtained were compressed into a predetermined form. The green compact materials were sintered at 1150-1300 ° C for 30 minutes under vacuum.

Cross-Tensile Strength and Rockwell Hardness, Scale A, (RA) at room temperature, transverse tensile strength at 900 ° C and weight gain by oxidation after holding at 900 ° C for 1 hour in still air samples of the hard alloys thus obtained are presented on the
Table 7.

 Samples Nos. 1 to 10 all exhibit extreme hardness and high transverse strength at room temperature fracture as well as high transverse tensile strength and excellent resistance to high temperature oxidation. A hot extrusion die was prepared using the hard alloy of sample number 6 and a pure copper rod was extruded through the die. It has been possible to extrude the rod 50 to 100 times satisfactorily. A similar die made of a hard alloy of the WC-Co type could not be used in practice for the hot extrusion of the pure copper rod.

COMPARATIVE EXAMPLES
The powders of compounds listed in Table 1 and the metal powders listed in Table 2 were blended to give the compositions shown in Table 1.
Table 4, the mixing ratios being presented on the
Table 6.

 The hard alloys were prepared by a method identical to that mentioned in the examples and the properties of these alloys are shown in Table 8.

Sample No. 11 has a W / B ratio of less than 0.75 and has a low transition resistance to breaking at room temperature, as well as at high temperature. Sample No. 12 has a low transverse fracture strength at high temperature and poor oxidation resistance due to an iron content of greater than 10% by weight, although it has a high transverse strength to the rupture at room temperature. Sample # 13, containing a MoCoB-type complex boride instead of the complex boride of the type
WCoB has a low transverse breaking strength at room temperature as well as at high temperature, compared to the samples of the examples having approximately the same hardness. Sample No. 14 containing a complex boride Mo2FeB2 type has a low transversal strength at the same time. rupture at high temperature and poor resistance to oxidation.

 A hot extrusion die similar to that described in the examples was prepared using the hard alloy of sample number 14, and a copper rod was extruded in the same manner as in the examples.

Only 5 to 10 extrusions were possible with the die.

Table 1

<tb> Podre <SEP> of <SEP> compound <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP > in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in
<tb><SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight
<tb><SEP> of <SEP> B <SEP> of <SEP> C <SEP> of <SEP> N <SEP> of <SEP> O <SEP> of <SEP> W <SEP> of <SEP> Fe <SEP> of <SEP> Cr <SEP> of <SEP> MB
<tb><SEP> WB <SEP> 5.5 <SEP> 0.03 <SEP> 0.1 <SEP> 0.07 <SEP> 94.3 <SEP> - <SEP> - <SEP> - <September>
<tb><SEP> CrB <SEP> 17.4 <SEP> 0.20 <SEP> 0.04 <SEP> 0.16 <SEP>#<SEP><SEP> = <SEP><SEP> 8Z, 2 <SEP><SEP> = <SEP>
<tb><SEP> MoB <SEP> 10.0 <SEP> 0.05 <SEP> 0.02 <SEP> 0.2 <SEP>#<SEP><SEP> 0.03 <SEP> - <SEP > 89.7
<Tb>
Table 2

<tb> Powder <SEP> Purity, <SEP>% <SEP> in <SEP> Powder <SEP> Purity, <SEP>% <SEP> in
<tb> metallic <SEP> weight <SEP> metallic <SEP> weight
<tb><SEP> W <SEP> 99.95 <SEP> Fe <SEP> 99.69
<tb><SEP> Cr <SEP> 99.75 <SEP> Cu <SEP> 99.9
<tb><SEP> Ni <SEP> 99.75 <SEP> Co <SEP> 99.87
<Tb>
Table 3

<tb> Echan- <SEP> Composition <SEP> (% <SEP> in <SEP> weight) <SEP> Report <SEP> Quantity <SEP> of
<tb> tillon <SEP> W / S <SEP> borure
<tb> N <SEP> B <SEP> W <SEP> Cr <SEP> Ni <SEP> Fe <SEP> Cu <SEP> Co <SEP> complex <SEP> (%
<tb><SEP> in <SEP> weight)
<tb><SEP> 1 <SEP>#<SEP><SEP> 3.0 <SEP> 51.4 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> the <SEP> remains <SEP> 1.0 <SEP> 71
<tb><SEP> 2 <SEP> 1,9 <SEP> 35,5 <SEP> 15,0 <SEP> - <SEP> - <SEP> - <SEP> the <SEP> remains <SEP> 1, 1 <SEP> 44
<tb><SEP> 3 <SEP>#<SEP><SEP> 1.9 <SEP> 42.0 <SEP> 10.0 <SEP> - <SEP> - <SEP> - <SEP> on <SEP > rest <SEP> 1,3 <SEP> 44
<tb><SEP> 4 <SEP>#<SEP><SEP> 2.2 <SEP> 29.9 <SEP> 15.0 <SEP> - <SEP> - <SEP> - <SEP> The <SEP > rest <SEP> 0.8 <SEP> 41
<tb><SEP> 5 <SEP>#<SEP><SEP> 3.0 <SEP> 53.4 <SEP> 5.0 <SEP>#<SEP> - <SEP> - <SEP> The <SEP > rest <SEP> 1.05 <SEP> 70
<tb><SEP> 6 <SEP> 2.0 <SEP> 34.3 <SEP> 21.0 <SEP> 5.0 <SEP>#<SEP><SEP> - <SEP> The <SEP> remains <SEP> 1.0 <SEP> 46
<tb><SEP> 7 <SEP> 3.8 <SEP> 58.2 <SEP> 5.0 <SEP> 1.0 <SEP>#<SEP><SEP>#<SEP><SEP><SEP> remainder <SEP> 0.9 <SEP> 80
<tb><SEP> 8 <SEP> 1.7 <SEP> 29.1 <SEP> 21.0 <SEP> 5.0 <SEP> 5.0 <SEP>#<SEP><SEP> the <SEP > rest <SEP> 1.0 <SEP> 39
<tb><SEP> 9 <SEP> 2.5 <SEP> 46.8 <SEP> 10.0 <SEP> 10.0 <SEP> 0.2 <SEP>#<SEP><SEP> the <SEP > rest <SEP> 1,1 <SEP> 58
<tb><SEP> 10 <SEP> 1.9 <SEP> 33.5 <SEP> 10.0 <SEP> 3.0 <SEP> - <SEP> 2.0 <SEP> The <SEP> remains <SEP> 1.0 <SEP> 44
<Tb>
Table 4

<tb> Echan- <SEP> Composition <SEP> (% <SEP> in <SEP> weight) <SEP> Report <SEP> Quantity <SEP> of
<tb> tillon <SEP> W / S <SEP> borure
<tb> N <SEP> complex
<tb><SEP> B <SEP> 3 <SEP> W <SEP> Cr <SEP> Ni <Sep> Fe <Sep> Cu <SEP> Co <SEP> (% <SEP> in <SEP>
<tb><SEP> weight
<tb><SEP> it <SEP> 11 <SEP> 2,4 <SEP> 28,6 <SEP> 7,0 <SEP> - <SEP> - <SEP> - <SEP> The <SEP> rest <SEP> 0.7 <SEP> 39
<tb><SEP> 12 <SEP> 12 <SEP> 3.0 <SEP> 51.4 <SEP> 5.0 <SEP> - <SEP> 15.0 <SEP> - <SEP> te <SEP> remainder <SEP> 1.0 <SEP> 70
<tb><SEP> 13 <SEP> 13 <SEP> 3.0 <SEP> - <SEP> 21.0 <SEP> 5.0 <SEP> - <SEP> 26.9 <SEP> the <SEP> remainder <SEP> - <SEP> MoCoB <SEP> 45
<tb><SEP> 14 <SEP> 4.0 <SEP> - <SEP> 17.1 <SEP> 10.0 <SEP> The <SEP> Remain <SEP> 33.7 <SEP> - <SEP> - <SEP> Mo2FeB2 <SEP> 57
<Tb>
Table 5

<tb> Sample <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP> in <SEP>% <SEP > in <SEP>% <SEP> in <SEP>% <SEP> in
<tb><SEP> N <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight
<tb><SEP> of <SEP> WB <SEP> of <SEP> W <SEP> of <SEP> Cr <SEP> of <SEP> Ni <SEP> of <SEP> Fe <SEP> of <SEP> Cu <SEP> of <SEP> CrB <SEP> of <SEP> Co
<tb><SEP> 1 <SEP> 54.5 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 45.5 <SEP>
<tb><SEP> 2 <SEP> 34.5 <SEP> 3.0 <SEP> 15.0 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 47.5
<tb><SEP> 3 <SEP> 34.5 <SEP> 9.5 <SEP> 10.0 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 46.0
<tb><SEP> 4 <SEP> 31.7 <SEP> - <SEP> 12.9 <SEP> - <SEP> - <SEP> - <SEP> 2.6 <SEP> 52.8
<tb><SEP> 5 <SEP> 54.5 <SEP> 2.0 <SEP> 5.0 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 38.5
<tb><SEP> 6 <SEP> 36.4 <SEP> - <SEP> 21.0 <SEP> 5.0 <SEP> - <SEP> - <SEP> - <SEP> 37.6
<tb><SEP> 7 <SEP> 61.7 <SEP> - <SEP> 3.0 <SEP> 1.0 <SEP> - <SEP> - <SEP> 2.4 <SEP> 31.9
<tb><SEP> 8 <SEP> 30.9 <SEP> - <SEP> 21.0 <SEP> 5.0 <SEP> 5.0 <SEP> - <SEP> - <SEP> 38.1
<tb><SEP> 9 <SEP> 45.5 <SEP> 3.9 <SEP> 10.0 <SEP> 10.0 <SEP> 0.2 <SEP> - <SEP> - <SEP> 30, 4
<tb><SEP> 10 <SEP> 34.5 <SEP> - <SEP> 10.0 <SEP> 3.0 <SEP> - <SEP> 2.0 <SEP> - <SEP> 50.5
<Tb>
Table 6

<tb> Sample <SEP>% <SEP> in <SEP> Z <SEP> in <SEP>% <SEP> in <SEP> X <SEP> in <SEP> X <SEP> in <SEP> X <SEP > in <SEP> Z <SEP> in <SEP>% <SEP> in
<tb><SEP> N <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight <SEP> weight
<tb><SEP> of <SEP> WB <SEP> of <SEP> W <SEP> of <SEP> Cr <SEP> of <SEP> Ni <SEP> of <SEP> Fe <SEP> of <SEP> MoB <SEP> of <SEP> CrB <SEP> of <SEP> Co
<tb><SEP> 11 <SEP> 30.3 <SEP> - <SEP> 3.5 <SEP> - <SEP> - <SEP> - <SEP> 4.2 <SEP> 62.0
<tb><SEP> 12 <SEP> 54.5 <SEP> - <SEP> 5.0 <SEP> - <SEP> 15.0 <SEP> - <SEP> - <SEP> 25.5
<tb><SEP> 13 <SEP> - <SEP> - <SEP> 21.0 <SEP> 5.0 <SEP> - <SEP> 30.0 <SEP> - <SEP> 44.0
<tb><SEP> 14 <SEP> - <SEP> - <SEP> 16.0 <SEP> 10.0 <SEP> 35.1 <SEP> 37.6 <SEP> = <SEP> 1.3 <SEP>
Table 7

<tb><SEP> Sample <SEP> N <SEP> Resistance <SEP> trans- <SEP> Hardness <SEP> (RA) <SEP> Resistance <SEP> Gain <SEP> of <SEP> Weight
<tb><SEP> pourable <SEP> to <SEP><SEP> rup- <SEP> cross <SEP> to <SEP> by <SEP> oxidation
<tb><SEP> ture <SEP> (temperature <SEP> ta <SEP> rupture <SEP> (mg / mm2 / h) <SEP>
<tb><SEP> ambient, <SEP> GPa) <SEP> (900 C, <SEP> GPa)
<tb> 1 <SEP>#<SEP><SEP> 1.95 <SEP> 82.7 <SEP> 1.79 <SEP> 9.76
<tb><SEP> 2 <SEP> 3.08 <SEP> 79.2 <SEP> 1.90 <SEP> 0.84
<tb><SEP> 3 <SEP> 2.67 <SEP> 79.2 <SEP> 1.94 <SEP> 1.27
<tb><SEP> 4 <SEP> 2.24 <SEP> 78.3 <SEP> 1.95 <SEP> 0.42
<tb><SEP> 5 <SEP> 2.29 <SEP> 84.5 <SEP> 1.97 <SEP> 4.24
<tb><SEP> 6 <SEP> 2.01 <SEP> 77.9 <SEP> 1.80 <SEP> 0.84
<tb><SEP> 7 <SEP> 1.85 <SEP> 89.5 <SEP> 1.71 <SEP> 3.18
<tb><SEP> 8 <SEP> 2.56 <SEP> 76.2 <SEP> 1.83 <SEP> 0.84
<tb><SEP> 9 <SEP> 2.46 <SEP> 80.8 <SEP> 2.03 <SEP> 1.15
<tb> 10 <SEP> 2.70 <SEP> 78.0 <SEP> 1.81 <SEP> 1.39
<Tb>
Table 8

<tb> Sample <SEP> N <SEP> Resistance <SEP> trans- <SEP> Hardness <SEP> (RA) <SEP> Resistance <SEP> trans- <SEP> Gain <SEP> of <SEP> Weight
<tb><SEP> versale <SEP> to <SEP> the <SEP> rup- <SEP> versale <SEP> to <SEP> the <SEP> rup- <SEP> by <SEP> oxidation
<tb><SEP> ture <SEP> (temperature <SEP> ture <SEP> (900 C, <SEP> GPa) <SEP> (mg / mm / h)
<tb><SEP> ambient, <SEP> GPa)
<tb><SEP> 11 <SEP> 1.63 <SEP> 81.6 <SEP> 1.42 <SEP> 6.37
<tb><SEP> 12 <SEP> 2.31 <SEP> 85.5 <SEP> 1.63 <SEP> 13.9
<tb><SEP> 13 <SEP> 1.81 <SEP> 78.7 <SEP> 1.28 <SEP> 1.63
<tb><SEP> 14 <SEP> 1.93 <SEP> 79.1 <SEP> 1.39 <SEP> 20.4
<Tb>
It goes without saying that the present invention has been described for explanatory purposes, but in no way limiting, and that many modifications can be made without departing from its scope.

Claims (4)

 1. Sintered hard alloy heat resistant, characterized in that it contains 35 to 95% by weight of a complex boride type WCoB in a cobalt-based alloy phase forming the matrix.  2. The heat-resistant sintered hard alloy according to claim 1, characterized in that it comprises 1.5 to 4.1% by weight of boron, 19.1 to 69.7% by weight of tungsten, the remainder being in cobalt and in a maximum amount of 1%, by weight of the alloy, unavoidable impurities.  The heat-resistant sintered hard alloy according to claim 2, characterized in that it further comprises chromium in an amount of 1 to 25% by weight.  4. Sintered heat resistant hard alloy according to claim 3, characterized in that it further comprises at least one element selected from nickel, iron and copper,  nickel, when present, substituting cobalt for 0.2 to 30% by weight of the amount of cobalt,  iron, when present, substituting cobalt for 0.2 to 15% by weight of the amount of cobalt, and  copper, when present, replacing the cobalt in a content of 0.1 to 7.5% by weight of the amount of cobalt.