GB2109409A

GB2109409A - Sintered hard alloy

Info

Publication number: GB2109409A
Application number: GB08229892A
Authority: GB
Inventors: Kenichi Takagi; Norio Nogita; Keizo Tamai; Masahito Fukumori; Seiichi Ohira; Tsuneyuki Ide; Hiroyuki Yamane; Tadao Watanabe; Yoshikazu Kondo
Original assignee: Toyo Kohan Co Ltd
Current assignee: Toyo Kohan Co Ltd
Priority date: 1981-10-19
Filing date: 1982-10-19
Publication date: 1983-06-02
Also published as: SE8205907L; DE3238555C2; JPS5867842A; DE3238555A1; FR2514788A1; SE8205907D0; JPS6057499B2; SE459504B; FR2514788B1; GB2109409B

Abstract

A sintered hard alloy, having excellent mechanical strength and toughness, comprises 40 to 95 % by weight of a hard phase composed of multiple borides containing at least 10 % by weight of Fe, and a binder phase for binding said hard phase, wherein the B content is 3 to 8%, the Cr content is up to 35 % by weight, the Ni content is up to 35 % by weight, the Al content is up to 2.85% by weight, the Si content is 0.03 to 4.75 % by weight, the C content is up to 0.95 % by weight, the 0 content us up to 2.3 % by weight, the content of Mo and/or W is such that the (Mo and/or W)/B atomic ratio is in the range of from 0.75 to 1.25 and the balance consists of Fe and unavoidable impurities.

Description

SPECIFICATION Sintered hard alloy The present invention relates to a sintered hard alloy comprising a hard phase composed mainly of multiple borides containing Fe and a binder phase for binding said hard phase. More particularly, the present invention relates to a sintered hard alloy having excellent mechanical strength and toughness Conventional hard materials, used are WC-based hard alloy, a stellite alloy and a high speed steel.

Recently, sintered hard alloys comprising a hard phase composed of iron boride or iron multiple boride have been proposed as materials capable of taking the place of these known hard materials in United States Patent No. 3,999,952 and Japanese Patent Publications No. 27818/79, No.8904/81 and 15773/81.

Sintered hard alloys disclosed in these proposals comprise a hard phase composed of iron boride or iron boride and a boride and/or multiple boride of at least one boride-forming element selected from Cr, Mo, W, Ti, V, Nb, Ta, Hf and Co and a binder phase composed of a metal selected from Fe, Cr, Ni, Mo, W, Ti, V, Nb, Ta, Hf, Zr and Cu and/or an alloy thereof.

The boride forming the hard phase is an intermetallic compound having a structure MB or M2B (in which M stands for a metal; the same will apply hereinafter), and the multiple boride is an intermetallic compound having a structure MXNyB (in which M and N stand for metals of the double boride; the same will apply hereinafter).

Furthermore, Japanese Patent Publication No.

15773/81 proposes a sintered hard alloy in which the hardness and toughness are improved by controlling the contents of Al, Si and 0.

It is a primary object of the present invention to provide a sintered hard alloy which is excellent in its mechanical strength and toughness and the stability thereof while it retains excellent corrosion resistance, oxidation resistance and wear resistance possessed by the above-mentioned conventional sintered hard alloys.

More specifically, in accordance with the present invention, there is provided a sintered hard alloy of excellent mechanical strength and toughness, which comprises 40 to 95% by weight of a hard phase composed of multiple borides containing at least 10% by weight of Fe and a binder phase for binding said hard phase, wherein the B content is 3 to 8%, the Cr content is up to 35% by weight, the Ni content is up to 35% by weight, the Al content is up to 2.85% by weight, the Si content is 0.03 to 4.75% by weight, the C content is up to 0.95% by weight, the 0 content is up to 2.3% by weight, the content of Mo and/or W is such that the (Mo and/or W)/B atomic ratio is in the range of from 0.75 to 1.25 and the balance consists of Fe and unavoidable impurities.

The present invention will now be described in detail. Incidentally, all of "%" given hereinafter are by weight.

The sintered hard alloy (often referred to as "sintered ailoy" hereinafter) of the present invention contains the main constituent elements at the abovementioned contents and the (Mo and/orW)/B atomic ratio is arranged in the range of from 0.75 to 1.25. By dint of this structural feature, the sintered alloy of the present invention shows a high stable transverse rupture strength of 175 to 300 Kg/mm2 when the Rockwell Ascale hardness (HRA) is in the range of from 80 to 93. The reason why the transverse rupture strength is high and the deviation thereof is reduced if the (Mo and/or W)/B atomic ratio is adjusted to about 1 has not completely been elucidated.As the result of the close examination, it was found that the Fe-containing multiple boride forming the hard phase comprises a boride of the Mo2FeB2 or WFeB type or a mixture thereof and minor amounts of such borides as MB, M2B and MxNvB. It also was confirmed that if the W content is high, a double boride of the W2FeB2 is present.

In the multiple boride of the Mo2FeB2, WFeB or W2FeB2 type, it is seen that Mo and W may be partially replaced with one another and Fe may be partially substituted with such elements as Cr, Ni and Co. The foregoing three multiple borides, inclusive of those where Mo and W may be partially substituted with each other and where Fe may be partially substituted with Cr, Ni and Co, will be hereinafter called multiple borides of the Mo2FeB2, WFeB and W2FeB2 types, respectively.

In order to form a hard phase composed mainly of these mutliple borides of the Mo2FeB2, WFeB or W2FeB2 types, it is indispensable that at least 10% of Fe should be contained in the hard phase.

In the sintered alloy of the present invention, Fe and the Fe-containing multiple boride are used for the following reasons. A sintered body of a boride containing Fe has sufficiently high hardness and toughness, and if an appropriate amount of Cr or Ni is added, there is attained excellent corrosion resistance, heat resistance and oxidation resistance comparable to those of stainless steel. Furthermore, a powder of a boride of Fe can easily be prepared on an industrial scale, and the Fe source is abundant and Fe is cheap.

The hardness of the sintered alloy of the present invention depends on the amount of the multiple boride forming the hard phase, the amount of the binder phase and the hardness of the binder phase.

The Rockwell A scale hardness of the sintered alloy of the present invention is in the range of from 80 to 93. In order to attain a Rockwell A scale hardness of at least 80, it is necessary that the amount of the hard phase should be at least 40%. If the amount of the hard phase exceeds 95%, the Rockwell A scale hardness is 93 or higher but the transverse rupture strength is lowerthan 175 Kg/mm2. Accordingly, the amount of the hard phase is adjusted to 40 to 95%.

The content of B which is the hard phase-forming element should be 3% so as to provide the minimum hard phase content of 40%, and the content of B 8% This print takes account of replacement documents later filed to enable the application to comply with the formal requirements of the Patents Rules 1982. is necessary for providing the maximum hardness content of 95%. Accordingly, the content of B is adjusted to 3 to 8%.

Mo and Ware elements forming the hard phase multiple boride as well as B, and if these elements are contained such that the (Mo and/or W)/B atomic ratio is in the range of from 0.75 to 1.25, such a high transverse rupture strength as 175 to 300 Kg/mm2 is attained in the sintered alloy of the present invention while the Rockwell A scale hardness is in the range of from 80 to 93. If the (Mo and/or W)/B atomic ratio is controlled in the range of from 0.90 to 1.20, a higher transverse rupture strength can be attained.

Accordingly, the content of Mo and/or W is adjusted such that the (Mo and/orW)/B atomic ratio is in the range of from 0.75 to 1.25, preferably from 0.90 to 1.20.

Cr improves the corrosion resistance, heat resistance and oxidation resistance of the sintered alloy of the present invention, and when Cr is used in combination with Ni, Cr exerts a function of rendering the sintered alloy of the present invention non-magnetic by austenitizing the binder phase.

When the sintered alloy of the present invention is used in the field where high mechanical strength and wear resistance are required but the corrosion resistance is not required, Cr need not particularly be added. However, in many cases, a high corrosion resistance is required as well as the above characteristics, and therefore, it is preferred that Cr be contained in an amount of at least 0.5%. If the Cr content exceeds 35%, the corrosion resistance, heat resistance and oxidation resistance are improved, but the mechanical strength is reduced and the transverse rupture strength is lowerthan 175 Kg/ mm2. Accordingly, the chromium content is adjusted to up to 35%, preferably 0.5 to 35%.

Ni is an element effective for improving the corrosion resistance and oxidation resistance, as well as Cr, and Ni is necessary for converting the structure of the binder phase to an austenitic non-magnetic material. If Ni is contained at a content of up to 35%, these objects can be attained.

Co is an element that can substitute mainly Fe in the boride of the Mo2FeB2, WFeB or W2FeB2 type forming the hard phase, and if the binder phase is a ferrite phase, Co exerts an effect of elevating the red hardness of the binder phase. However, if the Co content exceeds 35%, the transverse rupture strength is reduced below 175 Kg/mm2. Accordingly, the upper limit of the Co content is set at 35%.

Cu is an element which may be added for impro ving the hear conductivity and corrosion resistance of the sintered alloy of the present invention.

However, if the Cu content exceeds 35%, the hard ness and transverse rupture strength are reduced.

Accordingly, the Cu content is controlled to up to 35%.

Ti, Zr and Hf, belonging to the group Iva of the Periodic Table, and V, Nb and Ta, belonging to the group Va of the Periodic Table, substitute Mo or W of the multiple boride of the Mo2FeB2, WFeB or W2FeB2 type, and a part of such metal is consumed for alloying in the binder phase. These metals of the groups iVa and Va have effects of improving the hardness of the sintered alloy of the present invention and preventing coarsening of crystal grains at the time of the liquid phase sintering. Although these metals are generally expensive, high effects can be attained by incorporation of small amounts of these metals. If these metals of the groups IVa and Va are contained in a totai amount of up to 15% in view of the costs ofthese metals, both the hardness and the transverse rupture strength can be maintained at satisfactory levels.Accordingly, the total content of these metals is adjusted to up to 15%.

C is an element effective for reducing the oxides and increasing the hardness of the binder phase, and by these effects, the entire hardness of the sintered alloy of the present invention is increased.

However, if the content of C exceeds 0.95%, the hardness is not further improved but the transverse rupture strength is reduced. accordingly, the C content is controlled to up to 0.95%.

Al originates from the starting powder, and tends to react with B and 0 to form aluminum boride and aluminum oxide. Aluminum oxide has an adverse effect of reducing the sintering property of the sintered alloy of the present invention. Accordingly, it is preferred that the Al content be as low as possible. However, if the Al content is lower than 1%, the adverse effect of Al can substantially be neglected, and in the sintered alloy of the present invention, when incorporation ofO is controlled as much as possible, if the Al content is up to 2.85%, the adverse effect of Al is considerably moderated.

Accordingly, the Al content is controlled to up to 2.85%.

0 reacts with B, Cr, Al and Si to form oxides hindering the sintering property and causing reduction of the transverse rupture strength and broadening of the deviation thereof. Therefore, it is preferred that the 0 content be as low as possible. However, if the 0 content is up to 2.3%, the influence of 0 can substantially be neglected. Accordingly, the 0 content is controlled to up to 2.3%.

Si is an element which originates mainly from the starting powder. Si has effects of improving the sintering property of the sintered alloy of the present invention, increasing the density and hence improving the mechanical property of the sintered alloy of the present invention. However, if the Si content is lower than 0.03%, the effects are-not significant, and if the Si content exceeds 4.75%, the sintered alloy of the present invention becomes brittle. Accordingly, the Si content is controlled to 0.03 to 4.75%.

As taught in the above-mentioned Japanese Patent Publication, a powder of Fe-B or an alloy of the Fe-B type obtained by water or gas atomizing is used as the boron source. in some cases, a powder of ferroboron, a powder of boride of Ni, Cr, W, Ti or Mo or a powder of a single substance of B may be used as the boron source. Such a boron source may be mixed with powders of single substances of Mo, W, Ti, V, Fe, Cr, Ni, Co and Cu ar alloys containing two or more of these metals, and, if necessary, carbon powder or carbide is added. The resulting mixed powder is subjected to wet pulverization in an organic solvent in a vibration ball mill and then to drying, granulation and pressing. Then, the green compact is subjected to the liquid phase sintering in a non-oxidative atmosphere. Thus, the sintered alloy of the present invention is prepared.By adopting the liquid phase sintering technique, the density can be increased to substantially 100% in the sintered alloy of the present invention. In order to prevent oxidation at the sintering step, it is important that the sintering should be carried out in a non-oxidative atmosphere such as vacuum, a reducing gas or an inert gas. Ordinarily, the liquid phase sintering is conducted at 1100 to 1 400C for 5 to 90 minutes. If the sintering temperature is lower than 1100 C, a suffi cientamountofthe liquid phase is not produced and the sintering is not sufficiently advanced, resulting in formation of a sintered body full of voids.If the sintering temperature is higher than 1400 C, the liquid phase sintering is sufficiently advanced, but coarsening of crystal grains is caused and the transverse rupture strength is reduced. If the sintering time is shorter than 5 minutes, the density is not elevated to a satisfactory level, and even if the sintering time is longer than 90 minutes, the improvement of the strength corresponding to the prolongation of the sintering time cannot be attained, and in some case, reduction of the strength is caused. Accordingly, a sintering time longer than 90 minutes is not necessary.

The liquid phase sintering method which is effective for reducing formation of voids to a level as low as possible in the sintered alloy of the present invention has been described. However, it must be noted that this object can similarly be attained according to other sintering methods, for example, the hot isostatic pressing method, the hot pressing method and the electrical sintering method.

The present invention will now be described in detail with reference to the following Examples that by no means limit the scope of the invention.

The compositions of materials used in the following Examples and Comparative Examples are those shown in Tables 1,2 and 3 given hereinafter.

Example 1 A mixture of 20.2% of ferroboron powder A, 69.2% of ferrotungsten powder,2.1 of Cr powder, 1.1% of Ni powder, 7.1% of carbonyl Fe powder and 0.3% of C powder were wet-pulverized in a vibration ball mill with steel milling pots (vibration ball mills with steel milling pots were used in the subsequent Examples) for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1300 C.

Example 2 A mixture of 9.3% of ferroboron powder B.22.2% of ferrotungsten powder, 27.4% of W powder, 1.1% of Cr powder, 2.0% of Ni powder, 25.0% of WB powder, 12.7% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 3 A mixture of 31.1 % of B-containing alloy powder A,35.5% of Mo powder, 2.1% of Ni powder, 31.0% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1225 C.

Example 4 A mixture of 44.6% of B-containing alloy powder C,51.2% of Mo powder, 1.1% of Ni powder, 2.8% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1225 C.

Example 5 A mixture of 27.0% of ferroboron powder A, 39.1% of Mo powder,3.1 of Cr powder,1.1 of Ni powder,29.1 of MoB powder, 0.3% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 12750C.

Example 6 A mixture of 28.1% of B-containing alloy powder C,38.0% of ferrotungsten powder,16.7% of Mo powder, 0.5% of Cr powder, 0.5% of Ni powder, 16.0% of MoB powder and 0.2% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 7 A mixture of 32.3% of B-containing alloy powder C,28.0% of Mo powder, 0.6% of Cr powder, 2.1% of Ni powder, 36.7% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 12500C.

Example 8 A mixture of 44.6% of B-containing alloy powder C, 47.1% of Mo powder, 2.1% of Ni powder, 5.9% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 9 A mixture of 32.3% of B-containing alloy powder C, 44.8% of Mo powder, 0.6% of Cr powder, 2.1% of Ni powder, 19.9% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 10 A mixture of 27.6% nf ferroboron powder A,50.6% of Mo powder,2.3% of Cr powder,2.0% of Ni powder, 15.0% of MoB powder, 2.2% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 12750C.

Example 1? A mixture of 32.0% of B-containing alloy powder A,39.0% of Mo powder, 6.5% of Cr powder, 2.0% of Ni powder, 20.2% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 12 A mixture of 43.4% of B-containing alloy powder B,34.3% of Mo powder, 21.0% of Cr powder, 1.0% of Ni powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 13 A mixture of 30.3% of ferroboron powder A,41.9% of Mo powder, 2.1% of Cr powder, 25.4% of Ni powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1200 C.

Example 14 A mixture of 40.7% of B-containing alloy powder C, 9.5% of ferrotitanium powder,46.6% of Mo powder, 1.1% of Ni powder,1.8% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1300 C.

Example 15 A mixture of 42.0% of B-containing alloy powder C,7.3% of ferrovanadium powder, 50.4% of Mo powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Example 16 A mixture of 25.0% of B-containing alloy powder C,28.5% of Mo powder, 1.1% of Ni powder, 19.0% of Co powder, 25.3% of MoB powder, 0.8% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1225 C.

Example 17 A mixture of 25.0% of B-containing alloy powder C,28.5% of Mo powder, 0.9% of Cr powder, 1.0% of Ni powder, 19.0% of Cu powder, 25.3% of MoB powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1200 C.

Comparative Example 1 A mixture of 35.0% of ferroboron powder A,30.0% of Mo powder,3.0% of Cr powder,3.0% of Ni powder, 28.7% of carbonyl Fe powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1200 C.

Comparative Example 2 A mixture of 42.0% of B-containing alloy powder B,54.7% of Mo powder, 3.0% of Ni powder and 0.3% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1275 C.

Comparative Example 3 A mixture of 43.0% of B-containing alloy powder D,16.0% of B-containing alloy powder E,25.0% of Mo powder, 14.6% of Cr powder, 1.0% of Ni powder and 0.4% of C powder was wet-pulverized in a vibration ball mill for 28 hours, and the pulverized mixture was dried, granulated, pressed and sintered in vacuum at 1225 C.

Chemical analysis values, the (Mo and/or W)/B atomic ratios, the amounts of the hard phases and the Rockwell A scale hardness and transverse rupture strength values of the sintered alloys obtained in Examples 1 through 17 and Comparative Examples 1 through 3 are shown in Table 4.

Examples 1 through 5 show the relations of the B content to the amount of the hard phase, the Rockwell A scale hardness and the transverse rupture strength.

Examples 6 through 10 show the relations of the (Mo and/orW)/B atomic ratio to the amount of the hard phase, the Rockwell A scale hardness and the transverse rupture strength.

Examples 11 through 17 show the amount of the hard phase, the Rockwell A scale hardness and the transverse rupture strength when Cr, Ni, Ti as the metal of the group IVa, V as the metal of the group Va, Co and Cu were contained respectively.

Incidentally, Example 13 is an embodiment of a non-magnetic sintered alloy.

In Comparative Examples 1 and 3, the (Mo and/or W)/B atomic ratio was too low and was outside the range specified in the present invention.

In Comparative Example 2, the (Mo and/or W)/B atomic ratio was too high and was outside the range specified in the present invention.

From the results shown in Table 5, it is seen that the sintered alloys of the present invention were superior to the sintered alloys of the Comparative Examples in transverse rupture strength.

Table 1 Composition (% by weight) of B-Containing Alloy Powder Prepared by WaterAtomizing Sample Elements

B Cr W Mn Al Si O C Fe A 13.5 13.5 - 0.25 0.03 0.83 0.21 0.31 balance B 9.2 11.9 9.9 0.30 0.42 1.13 0.23 0.03 balance C 13.0 4.8 - 0.14 0.04 0.96 0.30 0.23 balance C 16.4 11.0 - 0.26 0.30 1.36 0.36 0.23 balance E 9.0 12.5 -V0.31 0.27 0.95 0.28 0.36 balance Table2 Composition (% by weight) of Alloy or Compound Sample Elements

B Fe Mo W Ti V Cr Mn Al Si O C Ferroboron A 15.6 balance - - - - 0.01 0.14 0.06 0.57 0.50 0.36 Ferroboron B 18.2 balance - - - - 0.00 0.21 0.08 0.59 0.43 0.41 Ferrotungsten balance 1.75 77.44 - - - 0.02 - 0.03 - 0.11 Ferrovanadium - balance - - - 82.91 - - 1.20 1.17 - 0.06 Ferrotitanium - balance - - 71.6 - - 0.06 0.03 0.04 - 0.06 MoB 10.0 0.05 balance - - - - - - - 0.05 0.03 WB 5.5 0.05 - balance - - - - - - 0.09 0.01 Table 3 Purities (% by weight) of Metal Powders and Carbon Powder

Powder Purity Carbonyl Fe 99.98 Mo 99.9 Cr 99.8 Ni 99.8 Co 99.9 W 99.9 Cu 99.9 C 99.9 Table 4 Chemical Analysis Values in Examples and Comparative Examples

Chemical Analysis Values (% by weight) No.

B B Mo W Ti V Cr Ni Co Cu Al Si C O Fe 1 3.0 - 51.0 - - 2.0 1.0 - - 0.01 0.13 0.15 0.06 balance 2 4.0 - 65.0 - - 1.0 1.9 - - 0.01 0.08 0.05 0.06 balance 3 4.0 35.5 - - - 4.0 2.0 - - 0.01 0.24 0.18 0.05 balance 4 5.5 48.8 - - - 2.0 1.0 - - 0.01 0.23 0.13 0.08 balance 5 6.7 62.1 - - - 3.0 1.0 - - 0.02 0.18 0.05 0.05 balance 6 5.0 29.6 28.3 - - 1.7 0.5 - - 0.01 0.28 0.05 0.05 balance 7 4.0 26.6 - - - 2.1 2.0 - - 0.01 0.28 0.07 0.04 balance Q ~ ~ ~ 8 8 5.5 44.9 ~ 2.0 2.0 0.02 0.43 0.11 0.08 balance E Co x 9 ~ 4.0 42.6 - - - 2.0 2.0 - - 0.01 0.29 0.10 0.02 balance 10 5.5 61.0 - - - 2.2 1.9 - - 0.02 0.17 0.09 0.03 balance 11 4.1 37.1 - - - 10.3 1.9 - - 0.01 0.25 0.10 0.03 balance 12 4.0 32.6 4.2 - - 24.9 1.0 - - 0.19 0.50 0.12 0.07 balance 13 4.5 39.9 - - - 2.0 24.1 - - 0.02 0.25 0.12 0.04 balance 14 5.0 44.4 - 6.5 - 1.9 1.0 ~ 0.02 0.39 0.12 0.12 balance 15 5.1 48.0 - - 5.8 1.9 - - - 0.10 0.47 0.14 0.04 balance 16 5.7 51.0 - - - 0.9 1.0 18.1 - 0.01 0.25 0.07 0.06 balance 17 5.5 48.8 - - - 2.0 1.0 - 18.1 0.01 0.22 0.09 0.06 balance 1 1 5.3 28.5 - - - 2.9 2.9 - - 0.02 0.19 0.12 0.06 balance Co 1 o > x 2 3.7 52.0 - - - 1.8 2.9 - - 0.18 0.45 0.11 0.06 balance O W W 3 8.1 23.8 - - - 20.9 1.0 - - 0.18 0.72 0.11 1.04 balance Table 5 (Mo andlor W)/B Atomic Ratios, Amounts of Hard Phases and Rockwell A Scale Hardness and Transverse Rupture Strength Values in Examples and Comparative Examples.

(Mo Amount Transverse andlor {% by Hard- Rupture W)IB Weightl ness Strength* No. Atomic ofHard (Kgimm2) Ratio Phase (HRA) Maximum Mean Value Value 1 1.00 70 83.0 245 220 2 0.96 93 92.8 202 183 3 1.00 50 84.8 296 283 4 1.00 69 90.2 262 233 5 5 1.04 87 91.2 221 216 6 1.00 80 91.8 195 182 7 0.75 49 82.0 183 176 8 0.92 63 89.8 242 222 a;; E 9 1.20 50 83.0 245 226 E Co 10 1.25 68 90.7 192 182 11 1.02 51 83.5 258 235 12 0.98 52 82.3 195 188 13 1.00 56 83.8 246 228 14 1.00 62 89.2 187 178 15 1.06 64 89.7 230 221 16 1.01 62 87.3 230 216 17 1.00 69 89.7 236 223 Co am 1 0.61 88 88.2 145 96 a; Co a; E 2 1.58 58 86.2 168 142 EW O ~ ul 3 0.33 91 91.1 103 65 Note ten samples were tested in each Example.

Claims

1. Asintered hard alloy having high mechanical strength and toughness, which comprises 50 to 95% by weight of a hard phase composed of multiple borides containing at least 10% by weight of Fe and binder phase for binding said hard phase, wherein the B content is 3 to 8%, the Cr content is up to 35% by weight, the Ni content is up to 35% by weight, the Al content is up to 2.85% by weight, the Si content is 0.03 to 4.75% by weight, the C content is up to 0.95% by weight, the 0 content is up to 2.3% by weight, the content of Mo and/or W is such that the (Mo and/or W)/B atomic ratio is in the range of from 0.75 to 1.25 and the balance consists of Fe and unavoidable impurities.

2. Asintered hard alloy as claimed in claim 1, wherein the content of Mo and/or W is such that the (Mo and/or W)/B atomic ratio is from 0.90 to 1.20.

3. A sintered hard alloy as claimed in claim 1 or 2, wherein the content of Cu or Co is up to 35%.

4. A sintered hard alloy as claimed in any of claims 1, 2 or 3, wherein the total content of at least one member selected from Ti, V, Nb, Ta, Hf and Zr is upto 15%.

5. A sintered hard alloy as claimed in ciaim 1, substantially as described herein in any one of the Examples.