CA1178092A - Hard alloy containing molybdenum - Google Patents
Hard alloy containing molybdenumInfo
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- CA1178092A CA1178092A CA000378520A CA378520A CA1178092A CA 1178092 A CA1178092 A CA 1178092A CA 000378520 A CA000378520 A CA 000378520A CA 378520 A CA378520 A CA 378520A CA 1178092 A CA1178092 A CA 1178092A
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Abstract
TITLE OF THE INVENTION
A hard alloy containing molybdenum ABSTRACT OF THE DISCLOSURE
This invention relates to a hard alloy comprising two phases of a hard phase consisting of at least one compound having crystal structure of simple hexagonal MC type (M: metal; C: carbon) selected from the group consisting of mixed carbides, carbonitrides and carboxynitrides of molybdenum and tungsten, and a binder phase consisting of at least one element selected from the group consisting of iron, cobalt and nickel, in which the hard phase is one prepared by carburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tungsten with a particle size of at most 1 micron, is of coarse particles with a mean particle size of at least 3 microns and has a uniform molybdenum to tung-sten ratio in the particles, and which has a gross composi-tion within the range of shaded portion ABCDEA in Fig. 1.
A hard alloy containing molybdenum ABSTRACT OF THE DISCLOSURE
This invention relates to a hard alloy comprising two phases of a hard phase consisting of at least one compound having crystal structure of simple hexagonal MC type (M: metal; C: carbon) selected from the group consisting of mixed carbides, carbonitrides and carboxynitrides of molybdenum and tungsten, and a binder phase consisting of at least one element selected from the group consisting of iron, cobalt and nickel, in which the hard phase is one prepared by carburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tungsten with a particle size of at most 1 micron, is of coarse particles with a mean particle size of at least 3 microns and has a uniform molybdenum to tung-sten ratio in the particles, and which has a gross composi-tion within the range of shaded portion ABCDEA in Fig. 1.
Description
l ~ACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to a hard alloy containing molybdenum and more particularly, it is concerned with a composition of a hard alloy comprising a hard phase consis-ting of at least one compound having a crystal structure of simple hexagonal MC type (M: metal, C: carbon) and a binder phase, which is suitable for use as a tool capable of resis-ting a high impact for a long time.
1. FIELD OF THE INVENTION
This invention relates to a hard alloy containing molybdenum and more particularly, it is concerned with a composition of a hard alloy comprising a hard phase consis-ting of at least one compound having a crystal structure of simple hexagonal MC type (M: metal, C: carbon) and a binder phase, which is suitable for use as a tool capable of resis-ting a high impact for a long time.
2. DESCRIPTION 0~ THE PRIOR ART
The first report on a (Mo, W)C base alloy is seen in British Patent No. 635,221~ This describes a process for producing the (Mo, W)C base alloy by nitriding oxides of molybdenum and tungsten in ammonia stream, carburising the nitrides with release of nitrogen~ adding an auxiliary metal in powder form to serve as a binder in the sintered alloy, and sintering. This alloy was new at that time as an alloy consisting of one or two carbides of (W, Mo)C and (W, Mo)2C
with a binder metal, but has not been put to practical use.
Molybdenum monocarbide (MoC) is considered as a use-ful substitute, since this carbide only has the same crystal structure, a simple hexagonal type, as tungsten carbide as well as mechanical properties similar to tungsten carbide.
However, the existence of the hexagonal molybdenum monocar-bide as a simple substance has remained in question to this date and thus an attempt to stabilize molybdenum has exclu-sively been carried out by forming a solid solution with tungsten carbide. This method was firstly reported by ~l.
Dawihl in 1950, but this solid solution was no~ examined in detail and the commercial worth was not found in those days.
~k -1- ~
117~ 9X~
l Of late, hawever, the study to utilize the solid X
solution (Mox~Jy)C where x + y = 1 has become active with the rise of the price of tungsten, It is very interesting why a study on this solid solution and an attempt to use the same has not been carried out so actively up to the present time.
In the prior art process for the production of a solid solution of MoC-WC, WC, Mo and C powders or W, Mo, C
and Co powders are mixed, charged in a carbon vessel and reacted at a temperature of 1660 to 2000 C (W. Dawhil:
"Zeitschrift f. Anorganische Chemie" 262 (1950) 212). In this case, cobalt serves to aid in forming the carbide and to dissolve molybdenum and carbon in the tungsten carbide.
In the absence of c~balt, it is very difficult to obtain a X
solid solution of (Mo, W)C When a (Mo, W)C powder obtained by this method is used for the production of a cemented car-bide alloy with a binder metal of cobalt as a substitute for WC, however, (Mo, W)C decomposes in the alloy to deposit needle crystals of (Mo "~)2C. Deposition of even a small amount of such a subcarbide with aggregation in the alloy causes deterioration of the strength of the alloy. For this reason, the use of MoC as a substitute for WC has not been attempted positively.
In a process for the production of mixed carbides, in general, carbides are heated in the presence of each other, optionally using a diffusion aiding agent such as cobalt, to give a uniform solid solution in most cases, but in the case of a composition of solid solution containing at least 70 'h of MoC, a uniform solid solution cannot be obtained by coun-ter diffusion only at a high temperature. This is due tothe fact that MoC is unstable at a high temperature and is decomposed into solid solutions such as (Mo, W)C1 x and (Mo, W)3C2 and, consequently, a solid solution (~lo, ~)C of '~C
117~309Z
l type cannot be formed only by cooling it. As a method of stabilizing this carbide, it has been proposed to react the components once at a high temperature, to effect diffusion of Mo2C and WC, and to hold the product at a low temperature for a long time (Japanese Patent ~.pplication (OPI) No.
146306/1976). However, a considerably long diffusion time and long recrystallization time are required for forming ~ ) rom (Mo~ W)C1-x and (Mo~ W)3~2 at a low tempera-ture. ~or the practice of this method on a commercial scale, the mixture should be heated for a long time in a furnace to obtain a complete carbide. ~his means that the productivity per furnace is lowered and a number of furnaces are thus reguired. When using a continuous furnace, on the other hand, a long furnace is necessary and mass production is difficult industrially.
Under the situation, we, the inventors, have made vari-ous efforts to provide a solid solution (Mo-W) in an economi-cal manner based on the thought that if an alloy consisting of a solid solution (Mo-W) can be prepared at a low cost and a (Mo-W)C powder as a hard material can readily be produced on a commercial scale, the use of these materials or their cemented carbide alloys will remarkably be enlarged and con-sequently, have reached an invention as disclosed in US Patent No. 4,216,009 which consists in a process for the production of an alloy powder containing molybdenum and tungsten and having a crystal structure of simple hexagonal WC type, com-prising mixing molybdenum and tungsten in the form of com-pounds thereof selected from the group consisting of oxides, hydroxides, chlorides, sulfates, nitrates, metallic acids, salts of metallic acids and mixtures thereof, the resulting mixture of the compounds having a particle size of at most 1 micron, reducing the mixture with at least one member selec-ted from the group consisting of hydrogen and ammonia to form 117809~
l an alloy powder of molybdenum and tungsten, and then car--burizing the alloy powder.
Furthermore, the inventors have proposed cemented carbide alloy as disclosed in Japanese Patent Application (OPI) Nos. 145,146/1980 and 148742/1980, which are suitable for impact resisting tools. ~he former invention provides an impact resisting cemented carbide alloy containing moly-bdenum, characterised in that the friction coefficient is less than 70 b of that between WC-Co type alloys and steels, but this alloy does not have a sufficient life, in particu-lar, in a use subject to repeated impacts because of conta-ining a hard phase of MC type in the alloy. The latter invention provides an impactresisting cemented carbide alloy comprising a hard phase of mixed carbides of moly-bdenum and tungsten of MC type and a binder phase of cobalt and nickel, represented by (MoxW1 x)Cz-(NiyCo1 y) where 0.5 ~ xC 0.95, 0.5 ~ y ~ 1.0 and 0.90 C z C 0.98, but this alloy does not have a long life under such a severe condi-tion as being subjected to high impacts for a long time.
SUMMARY OF THE INVEN~ION
It is an object of the present invention to provide a hard alloy containing molybdenum and tungsten.
It is another object of the present invention to pro-vide a hard alloy corresponding to a cemented carbide alloy consisting of a hard phase of tungsten carbide (WC) a part of which is replaced by molybdenum carbide (MoC) and a bin-der phase of an iron group metal.
It is a further object of the present invention to provide a hard alloy having a hard phase consisting of a carbide, carbonitride or carboxynitride of molybdenum and tungsten with simple hexagonal crystal structure of MC type 1~7~3092 1 and a binder phase consisting of a least one of iron, cobalt and nickel, in which the hard phase has a relatively large mean particle size and a uniform distribution of molybdenum and tungsten.
It is a still further object of the present invention to provide a hard alloy capable of resisting high impacts for a long time.
It is a still further object of the present invention to provide a tool suitable for use where a high resistance to cyclic loads is required.
These objects can be attained by a hard a]loy compris-ing two phases of a hard phase consisting at least one eom-pound having a crystal structure of simple hexagonal MC type -(M: metal; C: earbon) seleeted from tne group consisting of mixed earbides, earbonitrides and carboxynitrides of moly-bdenum and tungsten, and a binder phase consisting of at least one element seleeted from the group eonsisting of iron, eobalt and niekel, in whieh the hard phase is one prepared by earburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tungsten with a partiele size of 1 mieron or less, is of eoarse partieules with a mean partiele size of 3 mierons or more and has a uniform molybdenum to tung-sten ratio in the partieles, and whieh has a gross eomposition defined by the relationships:
0.1 ~x <0.9, 10 wt% ~y <70 wt%, and 4 wt% <~ y, wherein y is the binder eontent in wt% and x is the atomie ratio of W/(Mo + W).
The accompanying drawings are to illustrate the prin-cipal and merits of the present invention in more detail:
Fig. 1 is graphical representation of the composition of a hard alloy according to the present invention in the relationship of W/(Mo ~ W) atomic ratio and binder content.
-5a-r ~
~17809Z
l Fig. 2 is a graphical representation of the relation-ship between the carbon content in alloy and the change of the transverse rupture strength (TRS) in an (MoO 7Wo 3)C-35 wt ,~ Co alloy.
~ ig. 3 is a graph showing the results of a fatigue test of an (MoO 7WO 3)C-35 wt % Co alloy (~: MC-~ alloys;
O: r~C-M2C-~ alloys) in which a cyclic load ~ is applied.
~ ig. 4 is a micrograph, magnified 5,OOO times, of (MoO 5Wo 5)C according to the present invention, in which Mo and W are uniformly distributed.
~ ig. 5 is a micrograph, magnified 5,OOO times, of (M~ ~O 5)C according to the prior art, in which Mo/W ratio is not uniform in each particle.
DETAI~ED DESCRIPTION OF THE INVENTION
In accordance with the present invention, there is provided a hard alloy comprising two phases of a hard phase consisting of at least one compound having a crystal struc-ture of simple hexagonal rlc type (M. metal; C: carbon) sele-cted from the group consisting of mixed carbides, carbonit-rides and carboxynitrides of molybdenum and tungsten, and a binder phase consisting of at least one element selected from the group consisting of iron, cobalt and nickel, in which the hard phase is one prepared by carburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tung-sten with a particle size of 1 micron or less, is of coarse particles with a mean particle size of 3 microns or more and has a uniform molybdenum to tungsten ratio in the particles, and which has a gross composition within the shaded portion ~BCDE~ in ~ig. 1.
The inventors have hitherto made various efforts to improve (Mo W)C-iron group metal alloys and consequently, ~17~3~92 1 have found that uniform dispersion of granular or globular (Mo, W)2C (which will hereinafter be referred to as M2C) therein is effective for increasing the yield stress and breaking strength (US Patent No. 4,265,662), but this alloy is not suitable for a use where a high fatigue strength is required upon exposure to a high impact for a long time.
This is possibly due to that the dispersed (Mo, W)2C rather acts as a harmful element for this purpose. ~here a high fatigue strength is required upon exposure to a high impact for a long time, "crack propagation" is regarded as impor-tant rather than "crack initiation" and in particular, "crack propagation" tends to extend along the boundaries between the ha,r'd phase and binder metal with high probability. Thus, it is necessary to reduce the boundaries of the hard phase and bin-der metal and this can be achieved by increasing the particle size of the hard phase and the thickness of the binder phase.
The inventors have carried out a heading test of bolts by utility tools made of materials as shown in Table 1 by chan-ging the particle size of a hard phase in a considerably binder metal rich region, thus obtaining results as shown in Table 2:
Table Particle Compressive TRS* VHN**
Size of Strengt~
Carbide CA) (Kg/mm ) (Kg/mm2) (Mo, W)C-25 wt ~ Co (~) 5 327 270 760 (Mo, ~J)C-25 wt O Co ~B) 1 345 295 810 WC~22 wt ~ Co (C) 5 310 280 830 Note: * ~ransverse Rupture Strength *~ Vickers Hardness Number l Table 2 Die ~ife (Number of Samples Processed/Die) x 105 _ Alloy (A) x Alloy (B) - -x Alloy (C) x Note: Mark x means a broken point.
Test Conditions: workpiece: S45C Steel forging speed: 100 samples per minute As is evident from these results, the strength of an alloy and the die life are not always consistent with each other and the low hardness and low strength alloy with a coarse 2rain size exhibits the longest life. ~hat is, the tool can be used even after cracks or deformations occur. ~his sugg-ests that the life of a tool does not depend on the initia-tion of crack but depends on the propagation speed of crack leading to the overall breakage thereof.
~ herefore, the inventors have concentrated their ener-gies on preparation of a coarse grain carbide and consequen-tly, have found that it is more difficult to obtain an (Mo, W)C with a large particle size than WC since molybdenum has an effect of retarding particle growth. However, it is fur-ther found that when using particularly the solid solution (Mo-W) prepared by the process of US Patent No. 4,21G,009 as mentioned above, a carbide with a particle size o~ 3 microns or more can readily be obtained by controlling the carburiz-ing condition, for example, by adjusting the carburization temperature to a temperature which is sufficiently high but lower than the decomposition point of (Mo, W)C into ~I~,o, W)2C, for example, to 1450 C in the case of (~loO 7W0 3)C. For ~178Q9Z
l the preparation of a carbide with a larger particle size, e.g. 6 microns or more, the carburization is preferably carlied out after the solid solution (Mo-W) is suhjected to a heat treatment. ~he heat treatment is generally carrr-ied out at a temperature of 1100 to 1400 C for 1 to 5 hours in a stream of nitrogen or hydrogen. In the case of ~MoO 5 WO 5)C, for example, the solid solution is thermally treat-ed at 1300 C for 3 hours in a stream of nitrogen.
When WC, Mo2C and C are used as starting materials and subjected to carburization according to the prior art, on the other hand, it is very difficult to form a coarse carbide with a particle size of 3 microns or more, and even if coarse starting materials are used, there is only formed a carbide having a fluctuating Mo/W ratio in each particle, because the carbon in the carbide acts as a diffusion bar-rier. ~he use of sueh a carbide with a binder metal results in a nonuniform alloy which mechanical strength is low.
In view of the above described faets, it will clearly be understood that an alloy containing a coarse carbide with a partiele size of at least 3 mierons, in partieular, at least 5 mierons and having a desired mechanical property, i.e. impact resistance must be prepared by way of the process comprising reac-ting the solid solution of (Mo, W) with carbon, which is capable of forming a uniform and large particle size (Mo, W)C, and otherwise, preparation of such an alloy is impo-ssible.
As a result of our studies on the sintering phenomenon of an alloy consisting of two phases of (Mo, W)C and a binder metal in more detail, it is found that in (Mo, W)C base alloys, there does not take place growth of carbide particles due to Ostwald ripening of the dissolving and precipitating type which 1~7809Z
l can be seen in the ordinary WC base alloys, but there is found a very slow particle growth of diffusion rate-contro-lling t~pe. In the (Mo, W)C base alloys, the particle growth during sintering, which can be seen in the prior art WC base alloys, is scarcely expected and therefore, a car-bide to be used as a raw material must be of coarse parti-cles so as to prepare an alloy containing a hard phase with a large particle size.
Similarly, the inventors have conducted various expe-riments and measured typical properties in order to make clear the features of M2C precipitated alloys and M2C non-precipitated alloys.
Fig. 2 is a graphical representation of the relation-ship between the carbon content (~ by weight) and transverse rupture strength (Kg/mm2) in an (MoO 7Wo 3)C-35 weight ~ Co alloy. As is apparent therefrom, the transverse rupture strength lowers rapidly with precipitation of free carbon, but does not so lower even if M2C is precipitated. This is considered to be due to that the M2C phase is dispersed uni-formly and finely so that dispersion strengthening appears, but it is hardly related with the lowering of the transverse rupture strength.
Fig. 3 is a graph showing the results of a fatigue test of an (MoO 7Wo 3)C-35 weight ~ Co alloy, in which a static load at a certain level is applied to a sample cyclically.
It is apparent from these results that the M2C-precipitated alloy (MC-M2C-~ alloys represented by mark 0) is inferior to the M2C-nonprecipitated alloy (MC-~ alloys represented by mark O in fatigue strength. This is possibly due to that the M2C phase finely dispersed increases the boundaries between the hard phase and binder metal phase and acts as l an element to promote crack propaga-tion, since cracks pro-pagate predominantly along the boundaries between the hard phase and binder phase. In the case of wear resisting tools, in general, a high stress is intermittently applied for a long time and in addition, some factors of promoting crack propagation, such as thermal impact and corrosion embrittle-ment are entangled, so a high fatigue strength is required.
In such a case, M2C should not be precipitated.
M2C tends to aggregate and grow larger abnormally with the increase of the quantity thereof, which acts as a stress concentrating source causing to lower the fatigue toughness when high impact energy is applied.
As the same time, it is also proved by a field test that the quantity of M2C precipitated should be held as little as possible or reduced to substantially null for the purpose of displaying sufficiently the performance of a tool in a case where an alloy having a relatively large binder phase and a structure such that the mean free path of the binder phase is large is used.
~ he inventors have made further studies on a hard alloy consisting of (Mo, W)C and an iron group metal by changing the ratio of Mo and W and the amount of the iron group metal over a wide range and it is thus found that the two phase region {(MC + ~) zone} is about 1/3 of that of WC base alloys in the case of (MoO 7Wo 3)C base alloys, and about 1/5 of that of WC
base alloys in the case of (MoO 9Wo 1)C base alloys. When the binder metal is changed from cobalt to iron in order, some shift takes place in the two phase region, but there is little change in width. ~hese data are collected and arranged to give results as shown in Fig. 1 wherein the boundary line of ~i2C-precipitated zone and M2C-nonprecipitated zone is drawn i~7t309Z
l by line a.
Furthermore, the inventors have conducted a number of exeriments by changing the ratio of Mo and W and the quan-tity of iron group metals over a wide range and ahve thus found that when the critical wid-th of controlling carbon industrially is 0.07 % by weight, a zone wherein there is (MC + ~) zone in an amount of at least 0.07 % by weight as carbon can be represented by the relationship of q x r ~ 4.0, i.e. above line a in ~ig. 1, where the alloy compo-sition consists of (MOp~Jq)C - r weight % binder metal~ In other words, it is quantitatively determined that M2C tends to be precipitated with the increase of the ratio of Mo in the ordinary (Mo, W)C base alloys and the amount of a binder metal should be increased so as to suppress precipitation of M2C. For example, as can be seen from Fig. 1, the two phase region of (MC +~ ) free from precipitation of M2C and free carbon amounts to at most 0.07 % by weight as carbon content used as a parameter unless the amount of a binder metal is more than 13.5 % by weight in the case of (MoO 7Wo 3)C base alloys, and at least 20 ~ by weight of a binder metal is required for the similar width of carbon value in the case of (MoO 8W0 2)C base alloys. As a matter of course, line a is shifted above when (MC + ~) zone exceeds 0.07 ~ by weight as carbon content, wherein the two phase region of (MC +~ ) is stable.
Referring to ~ig. 1, the ground of limiting the W/(Mo +
W) ratio to 0.1 ~- ~0 + W ~ 0.9 is that if the ratio is less than 0.1, the carbide is so unstable that it tends to be decomposed into M2C while if more than 0.9, there is little effect of molybdenum as (Mo, W)C. The ground of limitin~
the amount of a binder metal to 10 to 70 % by weight is that if less than 10 ~ by weight, the alloy itself becomes so brittle that it cannot be used in fact, while if more than 117~9~:
l 70 ~ by weight, the sintering is so difficult that a desired shape cannot be held.
The iron group metal as a binder phase can na-turally dissolve Group IVa, Va and VIa met'~s and itis possible to X
add even other elements having solubility therein such as aluminum, silicon, calcium, silver, etc. with holding the -merits of the present invention.
The basic concept of the present invention can be held even when a part of molybdenum and tungsten carbide is rep-laced by a B1 type mixed carbide containing titanium, ~irconium, hafnium , vanadium, niobium, tantalum, chromium, molybdenum and/or tungsten in a proportion of 3O % by weight or less, preferably 0.5 to 25 ~ by weight~ -Furthermore, there is the similar relationship even in the case of an alloy wherein a part of C in the carbide is replaced by nitrogen and/or oxygen. Examples of the preferred embodiment in this case are as follows.
The first embodiment is incorporation of N in (W, Mo)C
to give (W, Mo)(C, N) whereby a stable starting material of hexagonal WC type can be obtained without a heat treatment for a long time.
The second embodiment is incorporation of O in (IJ, Mo)(C, N) to give (W, Mo)(C, N, O) which is more stable.
The third embodiment is incorporation of Cr in (W, Mo)(C, N) or (W, Mo)(C, N, O) to give (IJ, ilo, Cr)(C, N) or ('J, Mo, Cr)(C, M, O) whereby a starting material with a low weight and low price can be obtained.
1178(~9;~
l The fourth embodiment is that in the production of these starting material powders, a mixture of oxides, metals, carbides and/or carbon is exposed to an atmosphere having a nitrogen partial pressure of 300 Torr or more at a temperature of 700 C or higher in a part of the carbu-rization step to form a stable starting powder.
The fifth embodiment is that, when the above described starting powder is combined with an iron group metal, t~Jo or more kinds of hard phases of simple hexagonal WC type differing in composition are caused to be present in the finished alloy, thereby imparting a high toughness thereto.
In these five embodiments, a part of the MC type phase can also be replaced by a B1 type solid solution containing one or more of Group IVa, Va and VIa metals and non-metallic elements, or the ordinary additives to cemented carbides, such as silver, silicon, bismuth, copper, aluminum, etc. can also be added to the iron group binder metal with holding the merits of the present invention.
The above described embodiments will now be illust-rated in greater detail:
In the important system of the present invention wherein there are a simple hexagonal phase containing molybdenum and tungsten, it is found in the sintered alloy with a binder metal that, when A = ( N atom ~ ~ x (1 _ W atom %
(~o + W) atom ,' ~Mo + W) atom Y~
the suitable range of A is 0.005 ~ A C o.5 If ~ is less than the lower limit, the effect of nitrogen does not appear, while if more than the upper limit, sintering to give exce-llent properties is difficult. The most suitable range of A
is 0.01 ~ A ~ 0.4.
Concerning the effect of oxygen, it is found that, when B = (~ a~)tomato~m ~) x (1 ~ 0 + I~al)tom~t~m S')' t~le suitable range of B is 0.005 ~ B ~ 0.05. If B is lcss than 117~092 l the lower limit, there is no favourable effect of o~ygen, while if more than the upper limit, sintering is difficul-t to give excellent properties. The most suitable range of B is 0.01 ~ B ~ 0.0~.
On the other hand, a W/~io ratio is preferably 10/90 to 90J10, since if less than 10/90, the alloy is unstable, while if more than 90/10~ the merits of the replacement (light weight, low price) are substantially lost. The quan-tity of chromium used for replacing molybdenum or tungstenlO if 0.5 or less by atomic ratio of (W ~ Mo), since if more than 0.5, the alloy is brittle although the corrosion resi-stance is increased.
As well known in the art, it is advantageous for cut-ting tools to form a B1 type solid solution composed of at least one of Group IVa, Va and VIa metals such as titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum and tungsten with at least one of non-metallic components such as carbon, nitrogen and oxygen in addition to the simple hexagonal phase. The quantity of the B1 type solid solution is preferably changed depending upon the cutting use.
Concerning the quantity of nitrogen in this case, it is found as a result of our various experiments that, when the definition of A is changed to (Group IVa Va VIa metals atom c,~) x (1 - W atom % ), the suitable range Group IVa,Va,VIa metals atom %
of A is also 0.005 ~ A ~ 0.5 although a part of the nitrogen is occluded in the B1 type solid solution. The optimum range of A is 0.01 C A c o 4 Concerning the quantity~of oxygen, it is found as a result of our various experiments that, when the definition of B is changed to O atom %
Group IVa,Va,VIa metals atom ~) x (1 - W atom % ), the suitable range of Group IVa,Va,VIa metals atom ,a, ~17~09Z
l B is also o.oo5 C 3 ~ 0 5 The optimum range of B is 0.01 C B ~ 0.04.
As the binder metal, there is preferably used an iron group metal in a proportion of 10 to 70 ~ by weight based on the gross composition, since if less than 10 ~ by weight, the alloy is brittle and if more than 70 ~ by weight, the alloy is too soft.
For the preparation of starting materials, the reac-tion is carried out at a high temperature in a hydrogen lO atmosphere in the case of carburization of a (Mo, W) powder `
with carbon, reduction and carburization of oxide powders with carbon or combination thereof. At this time, it is found as a result of our studies on the decomposition nitrogen pressure of (Mo, W)(C, N) that the external nitro-gen pressure, depending on the temperature, should be 300 Torr or more at 700 C or higher at which the carbonitriza-tion reaction takes place. The coexistence of hydrogen is not always harmful, but it is desirable to adjust the quan-tity of hydrogen to at most two times as much as that of nitrogen, in particular, at most the same as that of nitro~
gen not so as to hinder the nitriding reaction. In the case of using an ammonia decomposition gas, it is necessary to enrich with nitrogen.
For the preparation of starting materials containing oxygen, the coexistence of carbon monoxide and carbon dioxide is required in an atmosphere. In this case, the quantity of hydrogen is not limited as described above, but should not exceed 50 ~O of the atmosphere. Heating and sintering in an atmosphere of nitrogen or carbon oxide is effective for the purpose of preventing an alloy sintered from denitrification or deoxidation.
The inventors have further made studies to develop an alloy having a higher wear resistance and toughness and -~G-1~780~Z
l consequently, have found that the deformation at a high temperature can remarkably be improved by changing tungsten carbide to a carbide composed of a solid solution of three elements, molybdenum, tungsten and chromium. ~hat is to say, a (Mo, ~)C-Co alloy has a higher hardness at a high temperature than a WC - Co alloy and, when Cr is further dissolved in this carbide, the hardness is further raised and the high temperature hardness is also improved. Thus, the disadvantages of the prior art I~C - Co alloy can be overcome by one effort. It is to be noted that the carbide phase consists of a solid solution of (Mo, W, Cr)C. It is also found that when Cr is dissolved in a solid solution of (Mo, W)C, the carbide particles can be made finer and sta-bilized as a monocarbide of (Mo, W, Cr)C. On the contrary, the known method of adding merely chromium to the binder phase has the disadvantages that it is impossible to make finer the carbide and the carbide phase is not stabilized as a monocarbide of a solid solution of (Mo, W~ Cr). ~he quantity of chromium to be added to the solid solution car-bide (Mo, ~)C ranges preferably 0.3 to 10 %j since if lessthan 0.~ %, the carbide cannot be made finer, while if more than 10 ,~, Cr3C2 is separated and precipitated in the alloy, resulting in lowering of the hardness.
In a further embodiment of the present invention, a part of the carbon in the solid solution carbide (Mo, 1~, Cr)C
is replaced by nitrogen, oxygen and/or hydrogen. ~hat is, it is assumed that if the carbon contained in (Mo, ~], Cr)C is added as solid and reacted with a reactivity of 100 ,~, the crystal is stabilized, but now it is found that incorporation of no-t only carbon but 21so nitrogen results in stabilization of the monocarbide as (Mo, l;~ Cr)(C:N) and furthcr incorpora-tion of o~-ygen and hydrogen stabilizes more the monocarbiae as (l~o, 1~, Cr)(CaNbOcHd)(a + b r c + d = 1), because if thcI~c 117~3092 l are defects in the carbide, the carbide is unstable during sintering and an M2C type mixed carbide precipitates needle-wise to thus lower the strength.
In a still further embodiment of the present invention, one or more of manganese, rhenium, copper, silver, zinc and gold are incorporated in the binder phase to change the micronstructure of the binder phase and to make non-magnetic.
~t the same time, it is found that, when these elements are added, the binder phase is alloyed, whereby the corrosion resistance of the alloy is improved.
In the last embodiment of the present invention, the toughness of the alloy can be raised by using, in combina-tion, two or more carbides having a simple hexagonal phase but differing in the ratio of Mo/W. The detailed reason of increasing the toughness if not clear, but it is assumed that when (Mo, W)C is separated into two phases, the solu-tion strain of both the phases is lowered to give a higher toughness than in the case of a single phase. ~ince at least an alloy consisting of a (MoxWy)C (y ~ x) phase having the similar property to that of WC and a (MoxWy)C (x ~ y) phase having the similar property to that of MoC has two properties, i.e. toughness of WC and heat and deformation resistance of MoC, this embodimen-t is advantageous more than when using one kind of (Mo, W)C only. ~IOSt preferably, the carbide is composed of WC or a solid solution of some MoC
dissolved in WC and a solid solution of WC dissolved in MoC
This corresponds to a case where the peak of plane (1, 0, 3) is separated in two in X-ray diffraction. Whether there are two or more simple hexagonal phases of (MoxW )C or not can be confirmed by observation using an optical microscope after etching with an alkaline solution of a hexacyanoferrate (III) or by XM~ observation.
The application or use range of the alloy of the pre-~7~309~
1 sent invention is as follows. For example, the alloy ofthe present invention can be used for wear resisting tools such as guide rollers, hot wire milling rollers, etc., and for cutting tools, because of having a toughness and hard-ness similar to or more than those of WC-Co alloys. In particular, when the alloy of the invention as a substrate is coated with one or more wear resisting ceramic layers such for example as of TiC~ TiN, A12O3, cutting tools more excellent in toughness as well as wear resistance can be obtained than the prior art tools having WC-Co type alloys as a substrate. As well known in the art,at this time, a decarburization layer called ~-phase is formed at the boun-dary between the substrate and coating layer and this appears similarly in the alloy of the present invention. In order to prevent the embrittlement directly under the coating layer due to decarburization, the presence of free carbon (FC) in the surface layer within a range of 3OO microns is effective without deteriorating the toughness.
) When using the alloy of the present invention as a watch frame, it shows more excellent properties as a watch frame than WC-Co type alloys, which are summarized below:
(1) Beautiful brightness can be given when the alloy is specularly finished.
(2) Grinding and polishing workings are possible.
The first report on a (Mo, W)C base alloy is seen in British Patent No. 635,221~ This describes a process for producing the (Mo, W)C base alloy by nitriding oxides of molybdenum and tungsten in ammonia stream, carburising the nitrides with release of nitrogen~ adding an auxiliary metal in powder form to serve as a binder in the sintered alloy, and sintering. This alloy was new at that time as an alloy consisting of one or two carbides of (W, Mo)C and (W, Mo)2C
with a binder metal, but has not been put to practical use.
Molybdenum monocarbide (MoC) is considered as a use-ful substitute, since this carbide only has the same crystal structure, a simple hexagonal type, as tungsten carbide as well as mechanical properties similar to tungsten carbide.
However, the existence of the hexagonal molybdenum monocar-bide as a simple substance has remained in question to this date and thus an attempt to stabilize molybdenum has exclu-sively been carried out by forming a solid solution with tungsten carbide. This method was firstly reported by ~l.
Dawihl in 1950, but this solid solution was no~ examined in detail and the commercial worth was not found in those days.
~k -1- ~
117~ 9X~
l Of late, hawever, the study to utilize the solid X
solution (Mox~Jy)C where x + y = 1 has become active with the rise of the price of tungsten, It is very interesting why a study on this solid solution and an attempt to use the same has not been carried out so actively up to the present time.
In the prior art process for the production of a solid solution of MoC-WC, WC, Mo and C powders or W, Mo, C
and Co powders are mixed, charged in a carbon vessel and reacted at a temperature of 1660 to 2000 C (W. Dawhil:
"Zeitschrift f. Anorganische Chemie" 262 (1950) 212). In this case, cobalt serves to aid in forming the carbide and to dissolve molybdenum and carbon in the tungsten carbide.
In the absence of c~balt, it is very difficult to obtain a X
solid solution of (Mo, W)C When a (Mo, W)C powder obtained by this method is used for the production of a cemented car-bide alloy with a binder metal of cobalt as a substitute for WC, however, (Mo, W)C decomposes in the alloy to deposit needle crystals of (Mo "~)2C. Deposition of even a small amount of such a subcarbide with aggregation in the alloy causes deterioration of the strength of the alloy. For this reason, the use of MoC as a substitute for WC has not been attempted positively.
In a process for the production of mixed carbides, in general, carbides are heated in the presence of each other, optionally using a diffusion aiding agent such as cobalt, to give a uniform solid solution in most cases, but in the case of a composition of solid solution containing at least 70 'h of MoC, a uniform solid solution cannot be obtained by coun-ter diffusion only at a high temperature. This is due tothe fact that MoC is unstable at a high temperature and is decomposed into solid solutions such as (Mo, W)C1 x and (Mo, W)3C2 and, consequently, a solid solution (~lo, ~)C of '~C
117~309Z
l type cannot be formed only by cooling it. As a method of stabilizing this carbide, it has been proposed to react the components once at a high temperature, to effect diffusion of Mo2C and WC, and to hold the product at a low temperature for a long time (Japanese Patent ~.pplication (OPI) No.
146306/1976). However, a considerably long diffusion time and long recrystallization time are required for forming ~ ) rom (Mo~ W)C1-x and (Mo~ W)3~2 at a low tempera-ture. ~or the practice of this method on a commercial scale, the mixture should be heated for a long time in a furnace to obtain a complete carbide. ~his means that the productivity per furnace is lowered and a number of furnaces are thus reguired. When using a continuous furnace, on the other hand, a long furnace is necessary and mass production is difficult industrially.
Under the situation, we, the inventors, have made vari-ous efforts to provide a solid solution (Mo-W) in an economi-cal manner based on the thought that if an alloy consisting of a solid solution (Mo-W) can be prepared at a low cost and a (Mo-W)C powder as a hard material can readily be produced on a commercial scale, the use of these materials or their cemented carbide alloys will remarkably be enlarged and con-sequently, have reached an invention as disclosed in US Patent No. 4,216,009 which consists in a process for the production of an alloy powder containing molybdenum and tungsten and having a crystal structure of simple hexagonal WC type, com-prising mixing molybdenum and tungsten in the form of com-pounds thereof selected from the group consisting of oxides, hydroxides, chlorides, sulfates, nitrates, metallic acids, salts of metallic acids and mixtures thereof, the resulting mixture of the compounds having a particle size of at most 1 micron, reducing the mixture with at least one member selec-ted from the group consisting of hydrogen and ammonia to form 117809~
l an alloy powder of molybdenum and tungsten, and then car--burizing the alloy powder.
Furthermore, the inventors have proposed cemented carbide alloy as disclosed in Japanese Patent Application (OPI) Nos. 145,146/1980 and 148742/1980, which are suitable for impact resisting tools. ~he former invention provides an impact resisting cemented carbide alloy containing moly-bdenum, characterised in that the friction coefficient is less than 70 b of that between WC-Co type alloys and steels, but this alloy does not have a sufficient life, in particu-lar, in a use subject to repeated impacts because of conta-ining a hard phase of MC type in the alloy. The latter invention provides an impactresisting cemented carbide alloy comprising a hard phase of mixed carbides of moly-bdenum and tungsten of MC type and a binder phase of cobalt and nickel, represented by (MoxW1 x)Cz-(NiyCo1 y) where 0.5 ~ xC 0.95, 0.5 ~ y ~ 1.0 and 0.90 C z C 0.98, but this alloy does not have a long life under such a severe condi-tion as being subjected to high impacts for a long time.
SUMMARY OF THE INVEN~ION
It is an object of the present invention to provide a hard alloy containing molybdenum and tungsten.
It is another object of the present invention to pro-vide a hard alloy corresponding to a cemented carbide alloy consisting of a hard phase of tungsten carbide (WC) a part of which is replaced by molybdenum carbide (MoC) and a bin-der phase of an iron group metal.
It is a further object of the present invention to provide a hard alloy having a hard phase consisting of a carbide, carbonitride or carboxynitride of molybdenum and tungsten with simple hexagonal crystal structure of MC type 1~7~3092 1 and a binder phase consisting of a least one of iron, cobalt and nickel, in which the hard phase has a relatively large mean particle size and a uniform distribution of molybdenum and tungsten.
It is a still further object of the present invention to provide a hard alloy capable of resisting high impacts for a long time.
It is a still further object of the present invention to provide a tool suitable for use where a high resistance to cyclic loads is required.
These objects can be attained by a hard a]loy compris-ing two phases of a hard phase consisting at least one eom-pound having a crystal structure of simple hexagonal MC type -(M: metal; C: earbon) seleeted from tne group consisting of mixed earbides, earbonitrides and carboxynitrides of moly-bdenum and tungsten, and a binder phase consisting of at least one element seleeted from the group eonsisting of iron, eobalt and niekel, in whieh the hard phase is one prepared by earburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tungsten with a partiele size of 1 mieron or less, is of eoarse partieules with a mean partiele size of 3 mierons or more and has a uniform molybdenum to tung-sten ratio in the partieles, and whieh has a gross eomposition defined by the relationships:
0.1 ~x <0.9, 10 wt% ~y <70 wt%, and 4 wt% <~ y, wherein y is the binder eontent in wt% and x is the atomie ratio of W/(Mo + W).
The accompanying drawings are to illustrate the prin-cipal and merits of the present invention in more detail:
Fig. 1 is graphical representation of the composition of a hard alloy according to the present invention in the relationship of W/(Mo ~ W) atomic ratio and binder content.
-5a-r ~
~17809Z
l Fig. 2 is a graphical representation of the relation-ship between the carbon content in alloy and the change of the transverse rupture strength (TRS) in an (MoO 7Wo 3)C-35 wt ,~ Co alloy.
~ ig. 3 is a graph showing the results of a fatigue test of an (MoO 7WO 3)C-35 wt % Co alloy (~: MC-~ alloys;
O: r~C-M2C-~ alloys) in which a cyclic load ~ is applied.
~ ig. 4 is a micrograph, magnified 5,OOO times, of (MoO 5Wo 5)C according to the present invention, in which Mo and W are uniformly distributed.
~ ig. 5 is a micrograph, magnified 5,OOO times, of (M~ ~O 5)C according to the prior art, in which Mo/W ratio is not uniform in each particle.
DETAI~ED DESCRIPTION OF THE INVENTION
In accordance with the present invention, there is provided a hard alloy comprising two phases of a hard phase consisting of at least one compound having a crystal struc-ture of simple hexagonal rlc type (M. metal; C: carbon) sele-cted from the group consisting of mixed carbides, carbonit-rides and carboxynitrides of molybdenum and tungsten, and a binder phase consisting of at least one element selected from the group consisting of iron, cobalt and nickel, in which the hard phase is one prepared by carburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tung-sten with a particle size of 1 micron or less, is of coarse particles with a mean particle size of 3 microns or more and has a uniform molybdenum to tungsten ratio in the particles, and which has a gross composition within the shaded portion ~BCDE~ in ~ig. 1.
The inventors have hitherto made various efforts to improve (Mo W)C-iron group metal alloys and consequently, ~17~3~92 1 have found that uniform dispersion of granular or globular (Mo, W)2C (which will hereinafter be referred to as M2C) therein is effective for increasing the yield stress and breaking strength (US Patent No. 4,265,662), but this alloy is not suitable for a use where a high fatigue strength is required upon exposure to a high impact for a long time.
This is possibly due to that the dispersed (Mo, W)2C rather acts as a harmful element for this purpose. ~here a high fatigue strength is required upon exposure to a high impact for a long time, "crack propagation" is regarded as impor-tant rather than "crack initiation" and in particular, "crack propagation" tends to extend along the boundaries between the ha,r'd phase and binder metal with high probability. Thus, it is necessary to reduce the boundaries of the hard phase and bin-der metal and this can be achieved by increasing the particle size of the hard phase and the thickness of the binder phase.
The inventors have carried out a heading test of bolts by utility tools made of materials as shown in Table 1 by chan-ging the particle size of a hard phase in a considerably binder metal rich region, thus obtaining results as shown in Table 2:
Table Particle Compressive TRS* VHN**
Size of Strengt~
Carbide CA) (Kg/mm ) (Kg/mm2) (Mo, W)C-25 wt ~ Co (~) 5 327 270 760 (Mo, ~J)C-25 wt O Co ~B) 1 345 295 810 WC~22 wt ~ Co (C) 5 310 280 830 Note: * ~ransverse Rupture Strength *~ Vickers Hardness Number l Table 2 Die ~ife (Number of Samples Processed/Die) x 105 _ Alloy (A) x Alloy (B) - -x Alloy (C) x Note: Mark x means a broken point.
Test Conditions: workpiece: S45C Steel forging speed: 100 samples per minute As is evident from these results, the strength of an alloy and the die life are not always consistent with each other and the low hardness and low strength alloy with a coarse 2rain size exhibits the longest life. ~hat is, the tool can be used even after cracks or deformations occur. ~his sugg-ests that the life of a tool does not depend on the initia-tion of crack but depends on the propagation speed of crack leading to the overall breakage thereof.
~ herefore, the inventors have concentrated their ener-gies on preparation of a coarse grain carbide and consequen-tly, have found that it is more difficult to obtain an (Mo, W)C with a large particle size than WC since molybdenum has an effect of retarding particle growth. However, it is fur-ther found that when using particularly the solid solution (Mo-W) prepared by the process of US Patent No. 4,21G,009 as mentioned above, a carbide with a particle size o~ 3 microns or more can readily be obtained by controlling the carburiz-ing condition, for example, by adjusting the carburization temperature to a temperature which is sufficiently high but lower than the decomposition point of (Mo, W)C into ~I~,o, W)2C, for example, to 1450 C in the case of (~loO 7W0 3)C. For ~178Q9Z
l the preparation of a carbide with a larger particle size, e.g. 6 microns or more, the carburization is preferably carlied out after the solid solution (Mo-W) is suhjected to a heat treatment. ~he heat treatment is generally carrr-ied out at a temperature of 1100 to 1400 C for 1 to 5 hours in a stream of nitrogen or hydrogen. In the case of ~MoO 5 WO 5)C, for example, the solid solution is thermally treat-ed at 1300 C for 3 hours in a stream of nitrogen.
When WC, Mo2C and C are used as starting materials and subjected to carburization according to the prior art, on the other hand, it is very difficult to form a coarse carbide with a particle size of 3 microns or more, and even if coarse starting materials are used, there is only formed a carbide having a fluctuating Mo/W ratio in each particle, because the carbon in the carbide acts as a diffusion bar-rier. ~he use of sueh a carbide with a binder metal results in a nonuniform alloy which mechanical strength is low.
In view of the above described faets, it will clearly be understood that an alloy containing a coarse carbide with a partiele size of at least 3 mierons, in partieular, at least 5 mierons and having a desired mechanical property, i.e. impact resistance must be prepared by way of the process comprising reac-ting the solid solution of (Mo, W) with carbon, which is capable of forming a uniform and large particle size (Mo, W)C, and otherwise, preparation of such an alloy is impo-ssible.
As a result of our studies on the sintering phenomenon of an alloy consisting of two phases of (Mo, W)C and a binder metal in more detail, it is found that in (Mo, W)C base alloys, there does not take place growth of carbide particles due to Ostwald ripening of the dissolving and precipitating type which 1~7809Z
l can be seen in the ordinary WC base alloys, but there is found a very slow particle growth of diffusion rate-contro-lling t~pe. In the (Mo, W)C base alloys, the particle growth during sintering, which can be seen in the prior art WC base alloys, is scarcely expected and therefore, a car-bide to be used as a raw material must be of coarse parti-cles so as to prepare an alloy containing a hard phase with a large particle size.
Similarly, the inventors have conducted various expe-riments and measured typical properties in order to make clear the features of M2C precipitated alloys and M2C non-precipitated alloys.
Fig. 2 is a graphical representation of the relation-ship between the carbon content (~ by weight) and transverse rupture strength (Kg/mm2) in an (MoO 7Wo 3)C-35 weight ~ Co alloy. As is apparent therefrom, the transverse rupture strength lowers rapidly with precipitation of free carbon, but does not so lower even if M2C is precipitated. This is considered to be due to that the M2C phase is dispersed uni-formly and finely so that dispersion strengthening appears, but it is hardly related with the lowering of the transverse rupture strength.
Fig. 3 is a graph showing the results of a fatigue test of an (MoO 7Wo 3)C-35 weight ~ Co alloy, in which a static load at a certain level is applied to a sample cyclically.
It is apparent from these results that the M2C-precipitated alloy (MC-M2C-~ alloys represented by mark 0) is inferior to the M2C-nonprecipitated alloy (MC-~ alloys represented by mark O in fatigue strength. This is possibly due to that the M2C phase finely dispersed increases the boundaries between the hard phase and binder metal phase and acts as l an element to promote crack propaga-tion, since cracks pro-pagate predominantly along the boundaries between the hard phase and binder phase. In the case of wear resisting tools, in general, a high stress is intermittently applied for a long time and in addition, some factors of promoting crack propagation, such as thermal impact and corrosion embrittle-ment are entangled, so a high fatigue strength is required.
In such a case, M2C should not be precipitated.
M2C tends to aggregate and grow larger abnormally with the increase of the quantity thereof, which acts as a stress concentrating source causing to lower the fatigue toughness when high impact energy is applied.
As the same time, it is also proved by a field test that the quantity of M2C precipitated should be held as little as possible or reduced to substantially null for the purpose of displaying sufficiently the performance of a tool in a case where an alloy having a relatively large binder phase and a structure such that the mean free path of the binder phase is large is used.
~ he inventors have made further studies on a hard alloy consisting of (Mo, W)C and an iron group metal by changing the ratio of Mo and W and the amount of the iron group metal over a wide range and it is thus found that the two phase region {(MC + ~) zone} is about 1/3 of that of WC base alloys in the case of (MoO 7Wo 3)C base alloys, and about 1/5 of that of WC
base alloys in the case of (MoO 9Wo 1)C base alloys. When the binder metal is changed from cobalt to iron in order, some shift takes place in the two phase region, but there is little change in width. ~hese data are collected and arranged to give results as shown in Fig. 1 wherein the boundary line of ~i2C-precipitated zone and M2C-nonprecipitated zone is drawn i~7t309Z
l by line a.
Furthermore, the inventors have conducted a number of exeriments by changing the ratio of Mo and W and the quan-tity of iron group metals over a wide range and ahve thus found that when the critical wid-th of controlling carbon industrially is 0.07 % by weight, a zone wherein there is (MC + ~) zone in an amount of at least 0.07 % by weight as carbon can be represented by the relationship of q x r ~ 4.0, i.e. above line a in ~ig. 1, where the alloy compo-sition consists of (MOp~Jq)C - r weight % binder metal~ In other words, it is quantitatively determined that M2C tends to be precipitated with the increase of the ratio of Mo in the ordinary (Mo, W)C base alloys and the amount of a binder metal should be increased so as to suppress precipitation of M2C. For example, as can be seen from Fig. 1, the two phase region of (MC +~ ) free from precipitation of M2C and free carbon amounts to at most 0.07 % by weight as carbon content used as a parameter unless the amount of a binder metal is more than 13.5 % by weight in the case of (MoO 7Wo 3)C base alloys, and at least 20 ~ by weight of a binder metal is required for the similar width of carbon value in the case of (MoO 8W0 2)C base alloys. As a matter of course, line a is shifted above when (MC + ~) zone exceeds 0.07 ~ by weight as carbon content, wherein the two phase region of (MC +~ ) is stable.
Referring to ~ig. 1, the ground of limiting the W/(Mo +
W) ratio to 0.1 ~- ~0 + W ~ 0.9 is that if the ratio is less than 0.1, the carbide is so unstable that it tends to be decomposed into M2C while if more than 0.9, there is little effect of molybdenum as (Mo, W)C. The ground of limitin~
the amount of a binder metal to 10 to 70 % by weight is that if less than 10 ~ by weight, the alloy itself becomes so brittle that it cannot be used in fact, while if more than 117~9~:
l 70 ~ by weight, the sintering is so difficult that a desired shape cannot be held.
The iron group metal as a binder phase can na-turally dissolve Group IVa, Va and VIa met'~s and itis possible to X
add even other elements having solubility therein such as aluminum, silicon, calcium, silver, etc. with holding the -merits of the present invention.
The basic concept of the present invention can be held even when a part of molybdenum and tungsten carbide is rep-laced by a B1 type mixed carbide containing titanium, ~irconium, hafnium , vanadium, niobium, tantalum, chromium, molybdenum and/or tungsten in a proportion of 3O % by weight or less, preferably 0.5 to 25 ~ by weight~ -Furthermore, there is the similar relationship even in the case of an alloy wherein a part of C in the carbide is replaced by nitrogen and/or oxygen. Examples of the preferred embodiment in this case are as follows.
The first embodiment is incorporation of N in (W, Mo)C
to give (W, Mo)(C, N) whereby a stable starting material of hexagonal WC type can be obtained without a heat treatment for a long time.
The second embodiment is incorporation of O in (IJ, Mo)(C, N) to give (W, Mo)(C, N, O) which is more stable.
The third embodiment is incorporation of Cr in (W, Mo)(C, N) or (W, Mo)(C, N, O) to give (IJ, ilo, Cr)(C, N) or ('J, Mo, Cr)(C, M, O) whereby a starting material with a low weight and low price can be obtained.
1178(~9;~
l The fourth embodiment is that in the production of these starting material powders, a mixture of oxides, metals, carbides and/or carbon is exposed to an atmosphere having a nitrogen partial pressure of 300 Torr or more at a temperature of 700 C or higher in a part of the carbu-rization step to form a stable starting powder.
The fifth embodiment is that, when the above described starting powder is combined with an iron group metal, t~Jo or more kinds of hard phases of simple hexagonal WC type differing in composition are caused to be present in the finished alloy, thereby imparting a high toughness thereto.
In these five embodiments, a part of the MC type phase can also be replaced by a B1 type solid solution containing one or more of Group IVa, Va and VIa metals and non-metallic elements, or the ordinary additives to cemented carbides, such as silver, silicon, bismuth, copper, aluminum, etc. can also be added to the iron group binder metal with holding the merits of the present invention.
The above described embodiments will now be illust-rated in greater detail:
In the important system of the present invention wherein there are a simple hexagonal phase containing molybdenum and tungsten, it is found in the sintered alloy with a binder metal that, when A = ( N atom ~ ~ x (1 _ W atom %
(~o + W) atom ,' ~Mo + W) atom Y~
the suitable range of A is 0.005 ~ A C o.5 If ~ is less than the lower limit, the effect of nitrogen does not appear, while if more than the upper limit, sintering to give exce-llent properties is difficult. The most suitable range of A
is 0.01 ~ A ~ 0.4.
Concerning the effect of oxygen, it is found that, when B = (~ a~)tomato~m ~) x (1 ~ 0 + I~al)tom~t~m S')' t~le suitable range of B is 0.005 ~ B ~ 0.05. If B is lcss than 117~092 l the lower limit, there is no favourable effect of o~ygen, while if more than the upper limit, sintering is difficul-t to give excellent properties. The most suitable range of B is 0.01 ~ B ~ 0.0~.
On the other hand, a W/~io ratio is preferably 10/90 to 90J10, since if less than 10/90, the alloy is unstable, while if more than 90/10~ the merits of the replacement (light weight, low price) are substantially lost. The quan-tity of chromium used for replacing molybdenum or tungstenlO if 0.5 or less by atomic ratio of (W ~ Mo), since if more than 0.5, the alloy is brittle although the corrosion resi-stance is increased.
As well known in the art, it is advantageous for cut-ting tools to form a B1 type solid solution composed of at least one of Group IVa, Va and VIa metals such as titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum and tungsten with at least one of non-metallic components such as carbon, nitrogen and oxygen in addition to the simple hexagonal phase. The quantity of the B1 type solid solution is preferably changed depending upon the cutting use.
Concerning the quantity of nitrogen in this case, it is found as a result of our various experiments that, when the definition of A is changed to (Group IVa Va VIa metals atom c,~) x (1 - W atom % ), the suitable range Group IVa,Va,VIa metals atom %
of A is also 0.005 ~ A ~ 0.5 although a part of the nitrogen is occluded in the B1 type solid solution. The optimum range of A is 0.01 C A c o 4 Concerning the quantity~of oxygen, it is found as a result of our various experiments that, when the definition of B is changed to O atom %
Group IVa,Va,VIa metals atom ~) x (1 - W atom % ), the suitable range of Group IVa,Va,VIa metals atom ,a, ~17~09Z
l B is also o.oo5 C 3 ~ 0 5 The optimum range of B is 0.01 C B ~ 0.04.
As the binder metal, there is preferably used an iron group metal in a proportion of 10 to 70 ~ by weight based on the gross composition, since if less than 10 ~ by weight, the alloy is brittle and if more than 70 ~ by weight, the alloy is too soft.
For the preparation of starting materials, the reac-tion is carried out at a high temperature in a hydrogen lO atmosphere in the case of carburization of a (Mo, W) powder `
with carbon, reduction and carburization of oxide powders with carbon or combination thereof. At this time, it is found as a result of our studies on the decomposition nitrogen pressure of (Mo, W)(C, N) that the external nitro-gen pressure, depending on the temperature, should be 300 Torr or more at 700 C or higher at which the carbonitriza-tion reaction takes place. The coexistence of hydrogen is not always harmful, but it is desirable to adjust the quan-tity of hydrogen to at most two times as much as that of nitrogen, in particular, at most the same as that of nitro~
gen not so as to hinder the nitriding reaction. In the case of using an ammonia decomposition gas, it is necessary to enrich with nitrogen.
For the preparation of starting materials containing oxygen, the coexistence of carbon monoxide and carbon dioxide is required in an atmosphere. In this case, the quantity of hydrogen is not limited as described above, but should not exceed 50 ~O of the atmosphere. Heating and sintering in an atmosphere of nitrogen or carbon oxide is effective for the purpose of preventing an alloy sintered from denitrification or deoxidation.
The inventors have further made studies to develop an alloy having a higher wear resistance and toughness and -~G-1~780~Z
l consequently, have found that the deformation at a high temperature can remarkably be improved by changing tungsten carbide to a carbide composed of a solid solution of three elements, molybdenum, tungsten and chromium. ~hat is to say, a (Mo, ~)C-Co alloy has a higher hardness at a high temperature than a WC - Co alloy and, when Cr is further dissolved in this carbide, the hardness is further raised and the high temperature hardness is also improved. Thus, the disadvantages of the prior art I~C - Co alloy can be overcome by one effort. It is to be noted that the carbide phase consists of a solid solution of (Mo, W, Cr)C. It is also found that when Cr is dissolved in a solid solution of (Mo, W)C, the carbide particles can be made finer and sta-bilized as a monocarbide of (Mo, W, Cr)C. On the contrary, the known method of adding merely chromium to the binder phase has the disadvantages that it is impossible to make finer the carbide and the carbide phase is not stabilized as a monocarbide of a solid solution of (Mo, W~ Cr). ~he quantity of chromium to be added to the solid solution car-bide (Mo, ~)C ranges preferably 0.3 to 10 %j since if lessthan 0.~ %, the carbide cannot be made finer, while if more than 10 ,~, Cr3C2 is separated and precipitated in the alloy, resulting in lowering of the hardness.
In a further embodiment of the present invention, a part of the carbon in the solid solution carbide (Mo, 1~, Cr)C
is replaced by nitrogen, oxygen and/or hydrogen. ~hat is, it is assumed that if the carbon contained in (Mo, ~], Cr)C is added as solid and reacted with a reactivity of 100 ,~, the crystal is stabilized, but now it is found that incorporation of no-t only carbon but 21so nitrogen results in stabilization of the monocarbide as (Mo, l;~ Cr)(C:N) and furthcr incorpora-tion of o~-ygen and hydrogen stabilizes more the monocarbiae as (l~o, 1~, Cr)(CaNbOcHd)(a + b r c + d = 1), because if thcI~c 117~3092 l are defects in the carbide, the carbide is unstable during sintering and an M2C type mixed carbide precipitates needle-wise to thus lower the strength.
In a still further embodiment of the present invention, one or more of manganese, rhenium, copper, silver, zinc and gold are incorporated in the binder phase to change the micronstructure of the binder phase and to make non-magnetic.
~t the same time, it is found that, when these elements are added, the binder phase is alloyed, whereby the corrosion resistance of the alloy is improved.
In the last embodiment of the present invention, the toughness of the alloy can be raised by using, in combina-tion, two or more carbides having a simple hexagonal phase but differing in the ratio of Mo/W. The detailed reason of increasing the toughness if not clear, but it is assumed that when (Mo, W)C is separated into two phases, the solu-tion strain of both the phases is lowered to give a higher toughness than in the case of a single phase. ~ince at least an alloy consisting of a (MoxWy)C (y ~ x) phase having the similar property to that of WC and a (MoxWy)C (x ~ y) phase having the similar property to that of MoC has two properties, i.e. toughness of WC and heat and deformation resistance of MoC, this embodimen-t is advantageous more than when using one kind of (Mo, W)C only. ~IOSt preferably, the carbide is composed of WC or a solid solution of some MoC
dissolved in WC and a solid solution of WC dissolved in MoC
This corresponds to a case where the peak of plane (1, 0, 3) is separated in two in X-ray diffraction. Whether there are two or more simple hexagonal phases of (MoxW )C or not can be confirmed by observation using an optical microscope after etching with an alkaline solution of a hexacyanoferrate (III) or by XM~ observation.
The application or use range of the alloy of the pre-~7~309~
1 sent invention is as follows. For example, the alloy ofthe present invention can be used for wear resisting tools such as guide rollers, hot wire milling rollers, etc., and for cutting tools, because of having a toughness and hard-ness similar to or more than those of WC-Co alloys. In particular, when the alloy of the invention as a substrate is coated with one or more wear resisting ceramic layers such for example as of TiC~ TiN, A12O3, cutting tools more excellent in toughness as well as wear resistance can be obtained than the prior art tools having WC-Co type alloys as a substrate. As well known in the art,at this time, a decarburization layer called ~-phase is formed at the boun-dary between the substrate and coating layer and this appears similarly in the alloy of the present invention. In order to prevent the embrittlement directly under the coating layer due to decarburization, the presence of free carbon (FC) in the surface layer within a range of 3OO microns is effective without deteriorating the toughness.
) When using the alloy of the present invention as a watch frame, it shows more excellent properties as a watch frame than WC-Co type alloys, which are summarized below:
(1) Beautiful brightness can be given when the alloy is specularly finished.
(2) Grinding and polishing workings are possible.
(3) Corrosion resistance is excellent, in particular, for sweat in the case of trinkets.
(4) Mechanical strength is considerably high.
The present invention will be further illustrated in greater detail in the following examples. It will be self-evident to those skill in the art that the ratios, ingre-dients in the following formulation and the order of opera-tions can be modified within the scope of thc preser.t inven-tion. Therefore, the present invention is not to be -1''-~171~)9Z
1 interpreted as being limite~ -to the fo1]owing examp]es. A11 parts, percents and the like are to be taken as those by weight unless otherwise indicated.
Example l 54 g of Mo powder and 46 g of W powder were dissolved in 28% aqueous ammonia, neutralized with 6 N hydrochloric acid to coprecipitate and then subjected three times to filtration with water washing and drying. In the resulting precipitate, WO3 and MoO3 were finely mixed. The mixed oxides were fired at 800C in the air and then reduced at 1000C in a hydrogen stream.
X-ray diffraction showed that the resulting powder was of a complete solid solution of (MoO 7Wo 3).
The resulting solid solution (MoO 7WO 3), carbon powder and Co powder as a diffusion aid were mixed in such a proportion that the final composition be (MoO.7WO 3)Cl O
carburization reaction at 1450C for l hour in a nitrogen stream under a nitrogen pressure of l atm. It was found by X-ray diffraction that the carbide had a crystal structure of simple hexagonal WC type and measurement of the particle size using Fisher Sub Sieve Sizer showed a mean particle size of 4.5 microns.
This powder was mixed with Co powder in such a proportion that the~ final composition be (MoO 7Wo 3)C - 30% Co, ball milled with alcohol medium, pressed in a desired shape and then sintered in a vacuum of lO 2 Torr. The thus obtained alloy had a structure consisting of two phases of MC phase and binder metal phase, and a hardness of 880 by Vickers hardness and a hending strength of 290 Kg/mm2.
Example 2 A solid solution of (MoO 5Wo 5) was prepared in an analogous manner to Example l except changing the Mo/W atomic ratio to 0.5 : 0.5. This solid solution was mixed with carbon . .
~7809Z
l powder and Co powder as a diffusion aid in such a proportion that the final compositin be (M0 5W0.5)C1.0 and subjected to carburization reaction at 1500 C for 1 hour in a nitro-gen stream under a nitrogen pressure of 1 atm. It was found by X-ray diffraction that the resulting carbide powder had a crystal structure of simple hexagonal WC type and by mea-surement of the particle size thereof using Fisher Sub Sieve Sizer that it had a mean particle size of 5.2 microns (Cf. Fig. 4).
This powder was mixed with ~Ti powder and Co powder in such a proportion that the final composition be (MoO 51~o 5)C
- 15 c~O Ni - 15 S Co, ball milled with alcohol medium, pres-sed in a desired shape and then sintered in a vacuum of 10-2 ~orr. The thus obtained alloy had 5.49 % of total carbon and 0.01 % of free carbon as analytical values, a structure consisting of two phases of MC and binder metals,and ahard-ness of 900 by ~ickers hardness and a bending strength of 300 Kg/mm .
For comparison, ~JC powder with a particle size of 4 microns, Mo2C powder with a particle size of 3.5 microns, carbon po~der and Co powder as a diffusion aid were mixed in such a proportion that the final composition be (MoO 51~lo 5)C1 0, and sintered at 1700 C in a vacuum of 10 Torr. The temperature was then lowered to 1350 C and the mixture was held at this temperature for 12 hours. X-ray diffraction showed that the resulting carbide was substan-tially of (Mo, W)C having a crystal structure of simple hexagonal WC type, but there were partly peahs of (Mo, W)2C
(Cf. Fig. 5).
This powder was mixed with Ni powder and Co powdcr in such a proportion that the final composition be (r~1OO 5Wo 5)C
- 15 ~ Ni - 15 ~ Co and an alloy was prepared in the same manner as described above. The thus obtaincd allo~r had l 5.48 90 of total carbon and 0.02 c~ of free carbon as analy-tical values, a structure consisting of MC phase, binder metal phase and M2C phase grown up through aggregation, and a hardness of 910 by Vickers hardness and a bending strength of 230 Kg/mm2 When using carbides as starting materials as in this comparative example, a uniform quality mixed carbide cannot always be obtained in the formation of the mixed carbide with a large particle size, and in an alloy obtained from this carbide, there is locally a carbon deficiency zone leading to formation of an aggregated M2C phase and resul-ting in lowering of the strength thereof.
Referring to ~ig. 4 and ~ig. 5, the heights of peaks of ~J and Mo show respectively the contents of 1J~I and Mo on the lines drawn in the micrographs of carbide crystals. It will be understood from comparison of ~ig. 4 and Fig. 5 that in the case of Fig. 4 according to the present invention, the fluctuation of peaks of 1~1 and Mo on the line crossing the carbide crystal is smaller, i.e. the Mo~J ratio is more constant, than in the case of ~ig. 5 according to the prior art.
~xample 3 Various alloys each having a composition within the range of shaded area of ~ig. 1 were prepared and subjected to measurement of the hardness and transverse rupture strength, thus obtaining results shown in Table 3. The sintering tem-perature ~JaS varied from 1200 C to 1450 C every composi-tion:
l Table 3 Sample No. Carbide ~inder Hardness ~R~
~ur-lnvention Composition Metal (Hv) (K~mm 1 (M0.85W0.15)C 30Ni-5Co 870 310 2 (M0~85W0~15)C 40Ni 720 280 3 ( 0.85 0.15) 30Co-30Ni 500 4 (MoO,7W0.3)c 10Ni-10Co 1150 260 (Mo0~70W0~3)c 15Ni-30Co 600 250 ( 0.7 0,3) 50Ni-15Co 445 7 (MoO 55W0 45)C 15Ni 1280 8 ( oO,50Wo.5o)c 20Ni-5Co 1020 265 9 (M0.3owo~7o)c 35Co 880 300 (MoO 30~J0 70)C 25Co-10~e 910 270 11 (MoO 30~0 70)C 8Fe-12Ni 1070 245 12 ~MoO 25W0 75)C 15Co-5Ni-8Fe 900 230 13 (MoO 20W0 80)C 15Ni-40Co 600 240 14 (MoO 20W0 80)C 30Fe 950 245 (MoO 20W0 80)C 10Ni-5Co 1260 240 16 (MoO 20W0 80)C 5Ni-5Co-2Fe1280 210 Comparison 17 (MoO 80W0 20)C 5Ni-5Co 1410 110 18 (MoO 70Wo 30)C 2Ni-4Co 1700 go 19 (MoO 50Wo 50)C 60Ni-15Fe 420 (MoO o5Wo 95)C 3Ni 1820 75 Example 4 The solid solution (MoO 5Wo 5) prepared in Example 2 was mixed with carbon powder, Cr3C2 powder and Co powder as a diffusion aid in such a proportion that the final compo-( 0~45~0~45cro~1o)c1 o~ subjected to primarycarburization at 1800 C for 1 hour in a hydrogen stre~m and then to secondary carburization at 1500 C for 1 hour in a hydrogen stream. It was found by X-ray diffraction that the ~7~309Z
l resulting powder had a crystal structure of simple hevagonal WC type and by measuremen-t of the particle size thereof that it had a mean particle size of 4.0 rnicrons.
This carbide powder was mixed with Ni powder and Co powder in such a proportion that the final composition be (MoO 45~lO 45CrO 10)C - 30 ~ Ni - 15 % Co and then sintered at 1220 C in a vacuurn of 10-2 morr. The thus obtained alloy had a struc-ture consisting of two phases oL MC and binder metals. When this alloy was polished with a diamond paste to gi~e a mirror surface and subjected to a test by immersing in an artificial sweat for 24 hours, there was hardly found corrosion thereof.
The alloy obtained in this example is suitable I or use as a watch frame because of its light weight as well as excellent scratch proofing property.
~ xample 5 Heading dies were made of the Alloy Sample I~os. 1, ~, 12 and 14 or ~xample 3 and WC - 25 ~ Co alloy for comparison and the life tests thereof were carried out by subjecting to cold forging of bolts of S45C steel, thus obtaining results shown in Table 4:
Table 4 Tool ~ife (Number of ~olts Processed/Die) x 10-~
Alloy Sample No. o 2 4 _ 6 8 -x o :~
14 x ~IC - 25 ,~ Co ~
-24_ ~809Z
l Example 6 910 g of the solid solution (Mo 7W0 3) prepared in Example 1 was mixed with 90 g of carbon powder and 3 g of cobalt powder as a diîustion aid and then subjected to (1) carburization at 1450 ~ for 1 hour in a nitrogen stream or (2) carburization at 1350 C for 1 hour in a nitrogen stream.
It was found by ~-ray diffraction that both of the resulting carbides were uniformly of (MoO 7Wo 3)C and measurement of the particle size of these carbides by means of ~isher Sub Sieve Sizer showed that the carbide prepared by the process (1) had a mean particle size of 4.2 microns, while the car-bide prepared by the process (2) had a mean particle size of 1.9 microns.
Each of these carbides was mixed with 30 % of cobalt powder, ball milled with alcohol medium, pressed in a desired shape and then sintered.
Heading dies were made of the thus obtained alloys and the life tests thereof were carried out by subjecting to cold forging of bolts of S45C steel, thus obtaining results shown in Table 5:
Table 5 Tool Life (Mumber of ~olts Processed/Die) x 105 ~lloy Sample Mo. 0 2 4 6 8 Alloy from x Process (1) x ~lloy from x Process (2) x Example 7 Piercing punches for punching a steel plate OI 5 mm in thickness were made of the Alloy Sample ~los. 7 and 15 of Example 3 and a WC - 12 ~' Co alloy for co;nparison and used -therefor 100,000 times. The amounvs of wear of the pier-cing punches at that time are shown in Table 6:
l Table 6 Allo~ Sample No. Amount of wear (mm) 7 0.07 0.08 ~IC - 12 ~ Co 0.21 Example 8 68.5 % of an (MoO 7l~10 3)C powder with a particle size of 3 microns, 30 % of Ni powder, 1 % of Mn powder and 0.5 %
of Re powder were mixed while adjusting the guantity of carbon to 97 ~ of the theoretical quantity 6.10 %, and the mixed powder was sintered at 1250 C for 1 hour in a vacuum of 10-2 Torr. The resulting alloy was non-magnetic and had the following properties:
Density: 9.9 g/cm3 Hardness (HRA): 84.5 Transverse Rupture Strength: 290 Kg/mm2 Example 9 75 ~ of an (MoO 5~llO 5)C powder with a mean particle size of 4 microns, 10 ~ of ~i powder, 13 $ of Co powder, 1 ,~ of Re powder, 0.8 c~ of Mg powder and 0.2 ~0 of B powder were mixed while adjusting the quantity of carbon to 98 ~
of th~ theoretical quantity of carbon 5.93 ~, and the mixed powder was sintered at 1350 C for 1 hour in a vacuum of 10-2 Torr. ~he resulting alloy had the following properties:
Density: 10.1 g/cm3 Hardness (HRA): 86.5 Transverse Rupture Strength: 265 Kg/mm2 ~or examination of the corrosion resistance, the above described alloy and a ~lC - 20 ~ Co alloy for comparison were subjected to tests using various corrosion solutions to give results as shown in Table 7:
ll7sasz Table 7 Amount of Corrosion (mg/cm2/hr) I* II** III***
l~lloy of Our Invention 2.5 0.2 0 WC - 20 ,~ Co 2.8 2.1 0 Note: I Ho. 10 ~;, I12S04 iSolu-tion II 35 ^ HCl Solution at Room Temperature III 10 f,S NaOH Solution at Room Temperature Example 10 30 ~' of an (MoO 7Wo 3)C powder with a mean particle size of 5 microns~ 35 % of an (MoO 3W0 7)C powder with a mean particle ~ize of 0.5 micron, 25 % of Ni powder and 10 ~ oî Co powder were mixed while adjusting the quantity of carbon to 97.5 " of the theoretical ~uantity of carbon, i.e.
The present invention will be further illustrated in greater detail in the following examples. It will be self-evident to those skill in the art that the ratios, ingre-dients in the following formulation and the order of opera-tions can be modified within the scope of thc preser.t inven-tion. Therefore, the present invention is not to be -1''-~171~)9Z
1 interpreted as being limite~ -to the fo1]owing examp]es. A11 parts, percents and the like are to be taken as those by weight unless otherwise indicated.
Example l 54 g of Mo powder and 46 g of W powder were dissolved in 28% aqueous ammonia, neutralized with 6 N hydrochloric acid to coprecipitate and then subjected three times to filtration with water washing and drying. In the resulting precipitate, WO3 and MoO3 were finely mixed. The mixed oxides were fired at 800C in the air and then reduced at 1000C in a hydrogen stream.
X-ray diffraction showed that the resulting powder was of a complete solid solution of (MoO 7Wo 3).
The resulting solid solution (MoO 7WO 3), carbon powder and Co powder as a diffusion aid were mixed in such a proportion that the final composition be (MoO.7WO 3)Cl O
carburization reaction at 1450C for l hour in a nitrogen stream under a nitrogen pressure of l atm. It was found by X-ray diffraction that the carbide had a crystal structure of simple hexagonal WC type and measurement of the particle size using Fisher Sub Sieve Sizer showed a mean particle size of 4.5 microns.
This powder was mixed with Co powder in such a proportion that the~ final composition be (MoO 7Wo 3)C - 30% Co, ball milled with alcohol medium, pressed in a desired shape and then sintered in a vacuum of lO 2 Torr. The thus obtained alloy had a structure consisting of two phases of MC phase and binder metal phase, and a hardness of 880 by Vickers hardness and a hending strength of 290 Kg/mm2.
Example 2 A solid solution of (MoO 5Wo 5) was prepared in an analogous manner to Example l except changing the Mo/W atomic ratio to 0.5 : 0.5. This solid solution was mixed with carbon . .
~7809Z
l powder and Co powder as a diffusion aid in such a proportion that the final compositin be (M0 5W0.5)C1.0 and subjected to carburization reaction at 1500 C for 1 hour in a nitro-gen stream under a nitrogen pressure of 1 atm. It was found by X-ray diffraction that the resulting carbide powder had a crystal structure of simple hexagonal WC type and by mea-surement of the particle size thereof using Fisher Sub Sieve Sizer that it had a mean particle size of 5.2 microns (Cf. Fig. 4).
This powder was mixed with ~Ti powder and Co powder in such a proportion that the final composition be (MoO 51~o 5)C
- 15 c~O Ni - 15 S Co, ball milled with alcohol medium, pres-sed in a desired shape and then sintered in a vacuum of 10-2 ~orr. The thus obtained alloy had 5.49 % of total carbon and 0.01 % of free carbon as analytical values, a structure consisting of two phases of MC and binder metals,and ahard-ness of 900 by ~ickers hardness and a bending strength of 300 Kg/mm .
For comparison, ~JC powder with a particle size of 4 microns, Mo2C powder with a particle size of 3.5 microns, carbon po~der and Co powder as a diffusion aid were mixed in such a proportion that the final composition be (MoO 51~lo 5)C1 0, and sintered at 1700 C in a vacuum of 10 Torr. The temperature was then lowered to 1350 C and the mixture was held at this temperature for 12 hours. X-ray diffraction showed that the resulting carbide was substan-tially of (Mo, W)C having a crystal structure of simple hexagonal WC type, but there were partly peahs of (Mo, W)2C
(Cf. Fig. 5).
This powder was mixed with Ni powder and Co powdcr in such a proportion that the final composition be (r~1OO 5Wo 5)C
- 15 ~ Ni - 15 ~ Co and an alloy was prepared in the same manner as described above. The thus obtaincd allo~r had l 5.48 90 of total carbon and 0.02 c~ of free carbon as analy-tical values, a structure consisting of MC phase, binder metal phase and M2C phase grown up through aggregation, and a hardness of 910 by Vickers hardness and a bending strength of 230 Kg/mm2 When using carbides as starting materials as in this comparative example, a uniform quality mixed carbide cannot always be obtained in the formation of the mixed carbide with a large particle size, and in an alloy obtained from this carbide, there is locally a carbon deficiency zone leading to formation of an aggregated M2C phase and resul-ting in lowering of the strength thereof.
Referring to ~ig. 4 and ~ig. 5, the heights of peaks of ~J and Mo show respectively the contents of 1J~I and Mo on the lines drawn in the micrographs of carbide crystals. It will be understood from comparison of ~ig. 4 and Fig. 5 that in the case of Fig. 4 according to the present invention, the fluctuation of peaks of 1~1 and Mo on the line crossing the carbide crystal is smaller, i.e. the Mo~J ratio is more constant, than in the case of ~ig. 5 according to the prior art.
~xample 3 Various alloys each having a composition within the range of shaded area of ~ig. 1 were prepared and subjected to measurement of the hardness and transverse rupture strength, thus obtaining results shown in Table 3. The sintering tem-perature ~JaS varied from 1200 C to 1450 C every composi-tion:
l Table 3 Sample No. Carbide ~inder Hardness ~R~
~ur-lnvention Composition Metal (Hv) (K~mm 1 (M0.85W0.15)C 30Ni-5Co 870 310 2 (M0~85W0~15)C 40Ni 720 280 3 ( 0.85 0.15) 30Co-30Ni 500 4 (MoO,7W0.3)c 10Ni-10Co 1150 260 (Mo0~70W0~3)c 15Ni-30Co 600 250 ( 0.7 0,3) 50Ni-15Co 445 7 (MoO 55W0 45)C 15Ni 1280 8 ( oO,50Wo.5o)c 20Ni-5Co 1020 265 9 (M0.3owo~7o)c 35Co 880 300 (MoO 30~J0 70)C 25Co-10~e 910 270 11 (MoO 30~0 70)C 8Fe-12Ni 1070 245 12 ~MoO 25W0 75)C 15Co-5Ni-8Fe 900 230 13 (MoO 20W0 80)C 15Ni-40Co 600 240 14 (MoO 20W0 80)C 30Fe 950 245 (MoO 20W0 80)C 10Ni-5Co 1260 240 16 (MoO 20W0 80)C 5Ni-5Co-2Fe1280 210 Comparison 17 (MoO 80W0 20)C 5Ni-5Co 1410 110 18 (MoO 70Wo 30)C 2Ni-4Co 1700 go 19 (MoO 50Wo 50)C 60Ni-15Fe 420 (MoO o5Wo 95)C 3Ni 1820 75 Example 4 The solid solution (MoO 5Wo 5) prepared in Example 2 was mixed with carbon powder, Cr3C2 powder and Co powder as a diffusion aid in such a proportion that the final compo-( 0~45~0~45cro~1o)c1 o~ subjected to primarycarburization at 1800 C for 1 hour in a hydrogen stre~m and then to secondary carburization at 1500 C for 1 hour in a hydrogen stream. It was found by X-ray diffraction that the ~7~309Z
l resulting powder had a crystal structure of simple hevagonal WC type and by measuremen-t of the particle size thereof that it had a mean particle size of 4.0 rnicrons.
This carbide powder was mixed with Ni powder and Co powder in such a proportion that the final composition be (MoO 45~lO 45CrO 10)C - 30 ~ Ni - 15 % Co and then sintered at 1220 C in a vacuurn of 10-2 morr. The thus obtained alloy had a struc-ture consisting of two phases oL MC and binder metals. When this alloy was polished with a diamond paste to gi~e a mirror surface and subjected to a test by immersing in an artificial sweat for 24 hours, there was hardly found corrosion thereof.
The alloy obtained in this example is suitable I or use as a watch frame because of its light weight as well as excellent scratch proofing property.
~ xample 5 Heading dies were made of the Alloy Sample I~os. 1, ~, 12 and 14 or ~xample 3 and WC - 25 ~ Co alloy for comparison and the life tests thereof were carried out by subjecting to cold forging of bolts of S45C steel, thus obtaining results shown in Table 4:
Table 4 Tool ~ife (Number of ~olts Processed/Die) x 10-~
Alloy Sample No. o 2 4 _ 6 8 -x o :~
14 x ~IC - 25 ,~ Co ~
-24_ ~809Z
l Example 6 910 g of the solid solution (Mo 7W0 3) prepared in Example 1 was mixed with 90 g of carbon powder and 3 g of cobalt powder as a diîustion aid and then subjected to (1) carburization at 1450 ~ for 1 hour in a nitrogen stream or (2) carburization at 1350 C for 1 hour in a nitrogen stream.
It was found by ~-ray diffraction that both of the resulting carbides were uniformly of (MoO 7Wo 3)C and measurement of the particle size of these carbides by means of ~isher Sub Sieve Sizer showed that the carbide prepared by the process (1) had a mean particle size of 4.2 microns, while the car-bide prepared by the process (2) had a mean particle size of 1.9 microns.
Each of these carbides was mixed with 30 % of cobalt powder, ball milled with alcohol medium, pressed in a desired shape and then sintered.
Heading dies were made of the thus obtained alloys and the life tests thereof were carried out by subjecting to cold forging of bolts of S45C steel, thus obtaining results shown in Table 5:
Table 5 Tool Life (Mumber of ~olts Processed/Die) x 105 ~lloy Sample Mo. 0 2 4 6 8 Alloy from x Process (1) x ~lloy from x Process (2) x Example 7 Piercing punches for punching a steel plate OI 5 mm in thickness were made of the Alloy Sample ~los. 7 and 15 of Example 3 and a WC - 12 ~' Co alloy for co;nparison and used -therefor 100,000 times. The amounvs of wear of the pier-cing punches at that time are shown in Table 6:
l Table 6 Allo~ Sample No. Amount of wear (mm) 7 0.07 0.08 ~IC - 12 ~ Co 0.21 Example 8 68.5 % of an (MoO 7l~10 3)C powder with a particle size of 3 microns, 30 % of Ni powder, 1 % of Mn powder and 0.5 %
of Re powder were mixed while adjusting the guantity of carbon to 97 ~ of the theoretical quantity 6.10 %, and the mixed powder was sintered at 1250 C for 1 hour in a vacuum of 10-2 Torr. The resulting alloy was non-magnetic and had the following properties:
Density: 9.9 g/cm3 Hardness (HRA): 84.5 Transverse Rupture Strength: 290 Kg/mm2 Example 9 75 ~ of an (MoO 5~llO 5)C powder with a mean particle size of 4 microns, 10 ~ of ~i powder, 13 $ of Co powder, 1 ,~ of Re powder, 0.8 c~ of Mg powder and 0.2 ~0 of B powder were mixed while adjusting the quantity of carbon to 98 ~
of th~ theoretical quantity of carbon 5.93 ~, and the mixed powder was sintered at 1350 C for 1 hour in a vacuum of 10-2 Torr. ~he resulting alloy had the following properties:
Density: 10.1 g/cm3 Hardness (HRA): 86.5 Transverse Rupture Strength: 265 Kg/mm2 ~or examination of the corrosion resistance, the above described alloy and a ~lC - 20 ~ Co alloy for comparison were subjected to tests using various corrosion solutions to give results as shown in Table 7:
ll7sasz Table 7 Amount of Corrosion (mg/cm2/hr) I* II** III***
l~lloy of Our Invention 2.5 0.2 0 WC - 20 ,~ Co 2.8 2.1 0 Note: I Ho. 10 ~;, I12S04 iSolu-tion II 35 ^ HCl Solution at Room Temperature III 10 f,S NaOH Solution at Room Temperature Example 10 30 ~' of an (MoO 7Wo 3)C powder with a mean particle size of 5 microns~ 35 % of an (MoO 3W0 7)C powder with a mean particle ~ize of 0.5 micron, 25 % of Ni powder and 10 ~ oî Co powder were mixed while adjusting the quantity of carbon to 97.5 " of the theoretical ~uantity of carbon, i.e.
5.15 ,~, and the mixed powder was sintered at 1320 C for hour in a vacuum of 10 Torr. The resulting alloy had the Eollowing properties:
Density: 11.2 g/cm~ Hardness (HRA): 82.5 Transverse P.upture Strength: 280 I~g/mm2 Heading dies for nut former were made of the above described alloy and a l~lC - 25 " Co alloy for comparison and the liEe tests thereof were carried out by cold forging nuts of S15C steel, thus obtaining results shown in Table 8:
Table 8 Tool Life (Number of Nuts Processed/Die) }~ 105 hllo;y Sample No. 0 2 4 6 8 10 12 I~lloy of Our Invention ~ (12.0) IJC -- 25 ~`J Co ~ (4.2)
Density: 11.2 g/cm~ Hardness (HRA): 82.5 Transverse P.upture Strength: 280 I~g/mm2 Heading dies for nut former were made of the above described alloy and a l~lC - 25 " Co alloy for comparison and the liEe tests thereof were carried out by cold forging nuts of S15C steel, thus obtaining results shown in Table 8:
Table 8 Tool Life (Number of Nuts Processed/Die) }~ 105 hllo;y Sample No. 0 2 4 6 8 10 12 I~lloy of Our Invention ~ (12.0) IJC -- 25 ~`J Co ~ (4.2)
Claims (14)
1. A hard alloy comprising two phases of a hard phase consisting of at least one compound having a crystal struc-ture of simple hexagonal MC type (M: metal; C: carbon) selected from the group consisting of mixed carbides, carbonitrides and carboxynitrides of molybdenum and tungsten, and a binder phase consisting of at least one element sele-cted from the group consisting of iron, cobalt and nickel, in which the hard phase is one prepared by carburizing an (Mo, W) alloy obtained by reducing oxides of molybdenum and tungsten with a particle size of at most 1 micron, is of coarse particles with a mean particle size of at least 3 microns and has a uniform molybdenum to tungsten ratio in the particles, and which has a gross composition within the range of shaded portion ABCDEA in Fig. 1.
2. The hard alloy of Claim 1, wherein the hard phase with a mean particle size of at least 3 microns is obtained by controlling the carburizing condition.
3. The hard alloy of Claim 2, wherein the carburi-zing condition is controlled by adjusting the carburization temperature to a temperature which is as high as possible but lower than the decomposition temperature of (Mo, W)C
into (Mo, W)2C.
into (Mo, W)2C.
4. The hard alloy of Claim 1, wherein the hard phase with a mean particle size of at least 3 microns is obtained by subjecting the (Mo, W) alloy to a heat treatment.
5. The hard alloy of Claim 4, wherein the heat treat-ment is carried out at a temperature of 1100 to 1400 °C in a stream of nitrogen or hydrogen.
6. The hard alloy of Claim 1, wherein a part of the compound of MC type is replaced by at least one hard 31-type compound selected from those containing Ti, Zr, Hf, V, Kb, Ta, Cr, Mo, and W.
7. The hard alloy of Claim 6, wherein the quantity of the B1 type hard compound replaced is at most 30 % by weight.
8. The hard alloy of Claim 1, wherein at least one of the mixed carbides is a solid solution of (Mo, W, Cr)C.
9. The hard alloy of Claim 8, wherein the quantity of Cr is 0.3 to 10 % by weight.
10. The hard alloy of Claim 1, wherein a part of the carbon in the carbides forming the hard phases is replaced by at least one of oxygen and nitrogen.
11. The hard alloy of Claim 10, wherein the quantities of nitrogen and oxygen are defined, in connection with the alloy composition, by the relationship of:
12. The hard alloy of Claim 1, wherein at least one element selected from the group consisting of Be, Mg, Ca, B, Si, P, Mn, Fe and Re is incorporated.
13. The hard alloy of Claim 1, wherein at least one of Mn, Re, Cu, Ag, Zn, and Au is incorporated in the binder phase to make the alloy non-magnetic.
14. The hard alloy of Claim 1, wherein the hard phase comprises two or three simple hexagonal phases differing in the ratio of Mo/W.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000378520A CA1178092A (en) | 1981-05-28 | 1981-05-28 | Hard alloy containing molybdenum |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000378520A CA1178092A (en) | 1981-05-28 | 1981-05-28 | Hard alloy containing molybdenum |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178092A true CA1178092A (en) | 1984-11-20 |
Family
ID=4120083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378520A Expired CA1178092A (en) | 1981-05-28 | 1981-05-28 | Hard alloy containing molybdenum |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1178092A (en) |
-
1981
- 1981-05-28 CA CA000378520A patent/CA1178092A/en not_active Expired
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