Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
I .t 6 4 ~! 9 3
1 BACKGROUND OF THE INVENTION
1~ FIELD OF THE INVENTION
The present invention relates to a process for the
production of a solid solution carbide of (Mo, W)C or a carbo-
nitride of (Mo, W)(CN), which are used as a raw material for
cemented carbide alloys, and more particularly, it is concerned
with a process for the production of such a carbide or carbo-
nitride with a uniform particle size.
2. DESCRIPTION OF THE PRIOR AR~
Up to the present time, as a starting material for
- cemented carbides, there has been used tungsten carbide (WC)
as a major component, but tung~ten is found in only a few parts
of the world and thus is very expensive. ~ately, the tendency
is to replace WC molybdenum carbide (MoC) having the ~ame cry-
stal structure as WC as well as mechanical properties similar
to WC and since MoC i8 un~table, MoC is stabilized by dissol-
ving WC therein to form a solid solution of (Mo, W)C which is
used as a starting material for cemented carbide alloys.
When using such a carbide or carbonitride as a raw
material for cemented carbides alloys or hard alloy~, it is
most important how to control the particle size of the hard
phase in the allo~s and the thickness of the binder phase corre-
3ponding thereto and to this end~ the particle size and evenness
of the raw material powder such a~ (Mo~ W)C or (Mo, W)(CN)
powder are most important for making even the particle size
and distribution there ofthe hard phase.
In the production of mixed carbides of Group IVa, Va
and VIa metal~ of Periodic ~able, metal oxides~ carbides and
carbon are mixed correspondingly to the compo~ition of an object
compound and reacted at a high temperature, or the reaction is
promoted by adding an additive to increase the diffusion rate.
When a solid solution i~ produced by the solid phase reaction
~.
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~ ~64~93
of powders, however, the degree of reaction is scattered depen-
ding on the mode of mixing the powders, the particle size and size di
tribution of the powders used. In order to form a uniform
solid solution, a heating operation for a long period oî time
is necessary as in the process described in Japanese Patent
Application (OPI) No. 146306/1976 in which a part of Mo in MoC
is replaced by W to stabilize the (Mo, W)C phase of simple
hexagonal type. ~hat is, in the production of a uniform solid
solution by the diffusion among powders of metals such as Mo
lO and W and carbides, heating at a high temperature such as 1600 C
or higher for a long time is required, in particular~ for diffu-
sing and dissolving metallic powders of Mo and W with a particle
size of several microns.
As a result of examining the particle size and the par-
ticle ~ize distribution of (Mo, W)C and (Mo, W)(CN) prepared
by such a known method, a reaction mechanism is found as shown
in Fig. 1. In the method as shown in Japanese Patent Applica-
tion (OPI) No. 146306/1976 and Japanese Patent Application (OPI)
No. 104617/1978 wherein predetermined amounts of MoC and WC to
20 give a final carbide (Mo, W)C are previously mixed, large amounts
of carbon and an iron group metal such as Co or Ni for stabili-
zing (Mo, W)C are added before the reaction (a-1). During the
course of the reaction, there appears once a stable form of
(Mo, W)2C + C(a-~), but when this is converted into (Mo, W)C
by a ~ubsequent heat treatment, the particle size or diameter
fluctuates (a-3).
If the powder particles are very fine, on the other
hand, diffusion proceeds well and a large amount of an iron
group metal as a diffusion aid is not required, resulting in
30 a good quality carbide. However, it is difficult on a commer-
cial scale to obtain powders of metals and carbides with a
particle size of 0.5 micron or less.
~ 1 648g3
1 We, the inventors, have hitherto found that when Mo
and W are mixed in the form of ammonium salts of Mo and W, in
the state of their solution~ or in the form of their oxides or
hailides, mixing can better be accomplished and a uniform solid
solution can more readily be obtained at a relatively low tem-
perature as compared with combinations of metal powders and/or
carbide powders. In this case, for example, W and Mo are uni-
formly mixed at the stage of forming their oxides and reduced
with hydrogen to form a solid solution of (Mo, W) which is
then reacted with carbon to give a solid solution carbide.
This has already been proposed as a commercially feasible
process (US Patent No. 4,216,009).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
process for the production of a hard solid solution containing
molybdenum.
It is another object of the present invention to provide
a process for the production of a solid solution carbide of
(Mo, W)C or a solid solution carbonitride of (Mo, W)(CN) having
an even particle size.
It is a further object of the present invention to
provide a process of producing a solid solution of (Mo, W)C or
(Mo, W)(CN) by two carburization stages.
~ hese object~ can be attained by a process for the pro-
duction of a hard solid solution con~tructed of at least one
hard phase having a crystalline structure of simple hexagonal
type, which process comprises preparing an alloy powder consis-
ting of a solid solution of molybdenum and tungsten, adding to
the alloy powder carbon in an amount sufficient to form
(Mo, W)2C and/or (Mo, W)2(CN), heating the mixture at a tempe-
rature at which (Mo, W)2C and/or (Mo, W)2(CN) is stable, adding
1 3 ~4~'33
1 to the (Mo, W)2C and/or (Mo, W)2(CN) carbon in an amount suffi-
c:;ent to form (Mo, W)C and/or (Mo, W)(CN) optionally with an
iron group metal and then heating the mixture at a temperature
at which (Mo, W)a and/or (Mo, W)(CN) is stable~
BRIEF DESCRIP~ION OF THE DRAWING
~ he accompanying drawings illustrate the principle and
merits of the present invention in more detail.
Fig. 1 and Fig. 2 show reaction models to illustrate
a process of formation of a solid solution (Mo, W)C, the model
of Fig. 1 being according to the prior art method and that of
Fig. 2 being according to the present invention.
Fig. 3 is a graph showing the relationship between the
carbon content and the strength as to alloys of the present
invention and comparative alloyæ of the prior art.
Fig. 4 and Fig. 5 are micrographs magnified 150 times
showing the dispersed state of (MoO 7Wo 3)2C as to alloys of
the present invention and the prior art respectively.
DETAILED DE~CRIP~ION OF ~HE INVENTION
~ he present invention aims at making uniform the par-
ticle size of a solid solution powder of (Mo, W)C and (Mo~ W)(CN)to be obtained finally. That i8 to say, the present invention
provides a process for the production of a solid solution con-
structed of at least one hard phase having a crystal structure
of simple hexagonal type and selected from mixed carbides or
carbonitrides of molybdenum and tungsten and solid sQlutions
of tungsten and molybdenum, which process comprises preparing
an alloy powder consisting of a solid solution of molybdenum
and tungsten, adding to the alloy powder carbon in an amount
necessary for forming (Mo, W)2C and/or (Mo, W)2(CN), heating
3o
~1~4~g3
l the mixture at a temperature at which ~Mo, W)2C and/or
(Mo, W)2(CN) is stable, adding to the (Mo, W)2C and/or
(Mo, W)2(CN) carbon in an amount necessary for forming (Mo, W3C
and/or (Mo, ~)(CN) optionally with an iron group metal and
then heating the mixture at a temperature at which (Mo, W)C
and/or (Mo, W)(CN) is stable.
In the process of the present invention, an alloy
powder containing molybdenum and tungsten is prepared b~ a
mixed powder obtained (1) by mixing an ammonium salt of
tungsten (e.g., ammonium tungstate) and an ammonium salt of
molybdenum (e.g., ammonium molybdate) in the form of a solu-
tion to coprecipitate parasalts of tungsten and molybdenum,
(2) by coprecipitating W03 and MoO3 with nitric acid or hydro-
chloric acid, or (~) by mixing previously prepared oxides or
hydroxides completely in a mechanical manner. Thus, the allo~
powder of (Mo, W) is previously synthesized, mixed with onl~
carbon in a minimum quantity necessary for forming (Mo, W)2C
and subjected to a primary reaction (Fig. 2, b-1). If the
reaction temperature is suitably chosen during the same time
as mentioned hereinafter, a uniform particle growth can be
carried out because of absence of excess carbon becoming a bar
to the particle growth of (Mo, W)2C. ~he (Mo, W)2C powder
(b-2) grown by this method is mixed with carbon in an amount
necessary for the final carbide composition and optionally
with an iron group metal such as Co or Ni (b-3), and subjected
to a secondary carburization at a temperature at which (Mo, W)C
is stable5 thus obtaining (Mo, W)C powder with a uniform parti~
cle size distribution (b-4).
In the case of producing a carbonitride of (Mo, W)(CN),
3 a mixture of carbon mixed in an analogous manner to the case
of (Mo, W)C is subjected to carburization steps in which the
carburization atmosphere is changed ~~ that containing N2
r
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l partly or throughout the steps.
For the practice of the present invention, it is desired
t~at the quantity of carbon to be added before the primary reac-
tion is in the range of z = 0.4 - 0.6 in carbides or carbonit-
rides represented respectively by (Mo, W)Cz or (Mo, W)(CN)z.
If z is less than 4, the carbide is not stabilized as (Mo, W)2C,
while if z is more than 0.6, the carbide after the primary reac-
tion is under such a state that (Mo, W)2C, (Mo, W)C and (Mo, W)~C2
coexist and thus a uniform particle growth is not carried out.
Moreover, it is desirable to control the quantity of carbon to
be added before the secondary reaction so that the final carbide
composition be in the range of z = 0.9 - 1.0 in (Mo, W)Cz or
(Mo, W)(CN)z. If z is less than 0.9, the strength of the final
alloy is insufficient, while if z exceeds 1.0, it is difficult
to sinter the final alloy.
Where the carbide or carbonitride is represented by (Ma Wb)Cz
Wb)(CN)z, the primary heating condition when a ~ 0.8 and
b c 0.2 is preferably 1400 C or higher. If lower than 1400 C,
(Mo, ~)2C is not so stabilized and, accordingly, a higher tem-
perature i~ rather desirable. On the contrary, the secondaryreaction is preferably carried out at a temperature of 1400 C
or lower.
When a C 0.8 and b ~ 0.2, the primary heating condition
is preferably 1400 C or higher, more preferably 1800 C or higher.
1~ seco~ala.^~
~ ) When the~carburiz~tion reaction is carried out at a temperature
. ~..
of 1800 C or lower, the carbide i~ stabilized as (Mo, W)C and
at a temperature of 1400 a or lower~ it is more stabilized.
In order to accomplish the reaction surely and in a short time,
it is further desired that the primary carbide is once cooled
to room temperature and then subjected to a treatment to impart
a mechanical ~train, such as grinding.
The following examples are given in order to illustrate
the present invention in detail without limiting the same.
g 3
1 Example 1
54 g of Mo powder and 46 g of W powder were dissolved
in 28 % aqueous ammonia and gradually neutralized with hydro-
chloric acid to precipitate needle crystals. The thus copre-
cipitated W03 and MoO3 were well mixed. These oxides were
~intered at 800 C in the air. The mixed powder was charged
in a Ni boat, covered and then reduced at 1000 C in an H2
stream to obtain an alloy powder of 2 microns.
The resulting alloy powder (MoO 7W0 3) was mixed with
4 5 ~ by weight of carbon powder and ball milled for 36 hours.
This mixed powder was reacted within a temperature range wherein
the subcarbide (MoO 7Wo 3)2C was stable, i.e. at 1900 C in an
H2 stream for 1 hour. The carbide was once cooled and ball
milled for 1 hour. Measurement of the particle size of the
(Moo 7Wo.3)2C powder showed that it was a uniform powder with
a particle size of 8 microns and a narrow particle size distri-
bution.
The primary carbide powder wa~ mixed with 4.5 % by
wei~ht of carbon powder and 1 % by weight of Co203 powder and
subjected again to carburization at a temperature at which the
monocarbide was stable, i.e. at 1400 C in an H2 stream. When
the properties of the resulting carbide were examined, it was
fou~d that the carbide Was a monocarbide of WC type containing
combined carbon in a substantially theoretical quantity as shown
in Table 1:
Table
Combined Carbon
Total Carbon Free Carbon Combined Carbon x 100
Theoretical Carbon
,,
8.9~ % 0.02 ~ 8.91 ~ 99.8 %
Example 2
A solid solution carbide of (MoO.85W0.15)
trial by the procedure of Example 1. An alloy powder of
i ~1 64~33
1 (~loO 85W0 15) was previously prepared in an analogous manner
to E`xample 1 and well mixed with 5.0~ by weight of carbon
powcier. The mixed powdex was charged in a graphite boat, heated
up to 1600C for a period of time of about 3 hours, held at
the maximum temperature for 1 hour and cooled to room tem-
perature for 10 hours. The quantity of carbon in the powder
i5 shown in Table 2. The reactivity was 50.2~. The analy-
tical result of X ray diffraction showed a peak of (Mo, W)2C
only.
Table 2
Total Carbon Free Carbon Combined Carbon Reactivity*
4.91 % 0.07 % 4.84 % 50.2
Note: * Reactivity = COmbined Carbon x 100
Theoretical Carbon
The subcarbide powder of ~o0.85W0.15)2C
mixed with 4% by weight of carbon powder and 0.3% by weight
of Co powder, charged in a Tammann-furnace and heated at
1250C for about 40 minutes in an H2 stream. The properties
of the resulting carbide were examined thus obtaining results
as shown in Table 3:
Table 3
Total Carbon Free Carbon Combined Carbon Reactivity
9.57 % 0.21 % 9.45 % 95 %
X ray diffraction showed that the peak of (Mo, W~2C sub-
stantially disappeared and the carbide had substantially a
crystal structure of WC type.
Example 3
The alloy powder of (MoO 7W0 3) obtained in an
analogous manner to Example 1 was mixed with 4.5~ by weight of
carbon powder and ball milled for 36 hours. The mixed powder
was reacted at 1800C in an N2 stream for 1 hour, cooled to
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1 room temperature and ball milled further for 1 hour. The
nitrogen content, as analysed in the powder, was 0.10%. The
resulting carbonitride of (MoO 7Wo 3)2(CN) was mixed with
4.:3% by weight of carbon powder and 0.3~ by weight of iron
powder and subjected to carburization at 1500C in an N2 stream,
thus obtaining a carbonitride with the following analytical
data:
Table 4
Total Carb n Free Carbon Combined Carbon Nitrogen Reactivit~
8.60 ~ 0.00 % 8.60 % 0.15 % 97.5 %
The thus resultant carbonitride had a particle size of 7 microns
and, according to X ray diffraction analysis thereof, there
was substantiall~ a peak of ~7C type with a neglifible amount
of ~Mo, W12C.
As ap~arent from these results, the carbides and
carbonitrides obtained according to the present invention had
a mean particle size of 4 to 8 microns, suitable for use as
a raw material of cemented carbides alloys for hot use.
Example 4
The alloy powder of ~MoO 5W0 5) obtained in an
analogous manner to Example 1 was mixed with 4.0% by weight of
carbon powder and ball milled for 36 hours. The mixed powder
was reacted at 1700C in an H2 stream for 1 hour, and cooled
to room temperature. The resulting ~oO 5Wo 5~2C powder was
then mixed with 4.0% by weight of carbon powder and 0.3~ by
weight of cobalt powder, and subjected to carburization at
1450C in an H2 stream, thus obtaining a carbide with the
following analytical data;
_ 9 _
I 1 6~93
1 Tàble 5
-
_tal Carbon Free Carbon Combined Carbon Nitrogen Reactivity
7.87 % 0.01 % 7.86 % 0.02 % 99.S %
Example S
The alloy powder prepared in Example 1 was mixed with
8.9% by weight of carbon powder, ball milled for 36 hours and
then reacted at 1700C in an H~ stream for 1 hour to form a
;Mo0 7W0 3)C powder (B).
The (Mo0 7W0 3~C powder (A) and (Mo O 7W0 3)C powder
(B) were respectively mixed with 30% by weight of Co in a
motar, compacted in a mold and sintered at 1300C in a high
vacuum of 10 4 mmHg or less for 1 hour. The ally ~C) from the
powder (A) and the alloy (D) from the powder ~B) were res-
pectively subjected to examination of the particle size dis-
tribution of the carbide using an image analyser, thus
obtaining results shown in Table 6:
Table 6 (~ by volume~ ~
d<0.5~0.5~-d<l~ 1~-d<3~3~-d~5~ 5~-d<10~ 10~-d
Our Alloy ~C) -0 0 0.9 11.1 77.9 10.1
20 Comparison
Alloy (D) 4.56.1 16.7 20.3 40.2 12.2
Note: d = particle diameter
Example 6
The ~Mo0 7Wo 3)C powder ~A) prepared in Example 1 and
the (Mo0 7Wo 3)C powder ~B~ prepared in Example 5 were res-
pectively mixed with 30% by weight of Co, ball milled by wet
process, compacted in mold and sintered at 1300C in a high
vacuum of 10 4 mmHg or less for 1 hour to obtain alloys
with the following properties:
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~.
~ 1648~3
1 Table 7
(Mo W 3)C powder Density Hardness Transverse
0 7 0 tg/cc) (HRA) Rupture
(Kg/mm2 )
-
Ou:r Alloy (E) A 10.2 83.5 290
Comparison
Alloy (E) ~ 10.2 83.0 250
Example 7
Header tools for nuts were made of Our Alloy ~E) and
Comparison Alloy ~E), prepared in Example 6, and used, for
test, as a header die for producing a wire rod of SCr 4. The
results are shown in Table 8 with those of a marketed WC-25 wt
Co-Alloy:
Table 8
i
Tool Life (x 10 4~
~ 10 20 30 40 50
I (pieces~
! Our Alloy ~ ~ o
o
- O
I Comparison x35
¦ - Alloy (F) x28
x46
WC-25%Co Alloy x17
xlO
- xll
o : usable x : broken
Example 8
The (MoO 7Wo 3~C powder ~ prepared in Example 1 and
the (MoO 7Wo 3)C powder (B) prepared in Example S were res-
pectively mixed with 35~ by weight of Co powder and in each
case, six sample alloys were prepared with varying the carbon
content in the range of 5.30 to 5.90% by weight. The properties
of these alloys are shown in Table 9:
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1 Table 9
Density Hardness Transverse Analytical Values
~g/cc) (IIRA) Rupture Total Carbon Free
Strength (%) Carbon
(Kg/mm2 ) ( % )
Our Alloy No.
1 10.0 82.6 185 5.32 0.00
2 10.0 82.9 260 5.46 0.00
3 10.0 82.3 320 5~60 0.00
4 10.0 82.4 295 5.72 0.00
9.9 82.3 230 5.80 0.06
6 9.9 82.4 180 5.90 0.15
7 10.0 82.3 180 5.30 0.00
8 10.0 82.2 167 5.48 0.00
~ 10.0 82.5 225 5.62 0.00
10.0 82.1 248 5.70 0.00
11 9.9 82.2 210 5.81 0.06
12 9.9 82.2 175 5.90 0.14
The alloys prepared in Example 8 were subjected to
Charpy test, thus obtaining results shown in Fig. 3 ~Curve A:
Alloy Nos. 1-6 of the present invention; Curve B: alloy Nos. 7-12
of the prior art~.
The alloys of Example 8 (No. 2 and No. 81 were com-
pared as to the dispersed state of (Mo0 7Wo 3)C by taking
micrographs magnified 150 times, as shown in Fig. 4 and
Fig. 5 respecti~ely.
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