Note: Descriptions are shown in the official language in which they were submitted.
~ l U ~
~ '~092/18656 I PCT/SE92/00234
.
M~THOD ~F M~ING C~MENTED CARBID~ ARTICL~S
The present invention relates to a method of making ce-
mented carbide articles using binder phase powders with
spherical, non-agglomerated particles.
Cemented carbide mainly contains tungsten carbide and
cobalt, often along with certain other carbides, e.g.
carbides of titanium, tantalum, niobium, chromium etc.
It contains at least one hard but brittle (carbide)
phase and a relatively less hard but ductile and tough
metal, particularly cobalt. This results in materials
combining hardness and toughness which have found many
applications, for instance in rock drilling and metal
cutting tools, in wear parts etc.
~'
Cemented carbide is made by techniques usual in powder
metallurgy, that is :
:,
- mixing the constituent powders (carbides, cobalt, and
possibly other hard materials) by milling, using mills
(rotating ball mills, vibrating mills, attritor mills
etc) equipped with non-polluting milling media which
themselves are made of cemented carbide. The milling is
made in the presence of an organic liquid (for instance
- ethyl alcohol, acetone, etc) and an organic binder (for
instance paraffin, polyethylene glycol, etc) in order to
facilitate the subsequent granulation operation.
:`
- granulation of the milled mixture according to known
techniques, in particular spray-drying. The suspension
containing the powdered materials mixed with the organic
liquid and the organic binder is atomised through an ap-
propriate nozzle in the drying tower where the small
drops are instantaneously dried by a stream of hot gas,
for instance in a stream of nitrogen. The granules col-
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2~08:l31
WO92/186S6 2 PCT/SE92/00234f
lected at the lower end of the tower have an average di-
ameter adjustable by the choice of appropriate nozzles,
between lO0 and 200 ~m. Such granules flow easily, in
contrast to fine or ultrafine powders. The formation of
granules is necessary in particular for the automatic
feeding of compacting tools used in the subsequent
stage.
- compaction of the granulated powder in a matrix with
punches (uniaxial compaction) or in a bag (isostatic
compaction), in order to give the material the shape and
dimensions as close as possible (considering the pheno-
menon of shrinkage) to the dimension wished for the fi-
nal body. If necessary, the compacted body can be sub-
jected to a machining operation before sintering.
- sintering of the compacted bodies at a temperature and
during a time sufficient for obtaining dense bodies with
a suitable structural homogeneity.
The sintering can equally be carried out at high gas
pressure (hot isostatic pressing), or the sintering can
~ be complemented by a sintering treatment under moderate
;~ gas pressure (process generally known as SINTER-HIP).
: 25
The sintered cemented carbides can be characterised in
. particular by their porosity and their microstructure
.. (observed by optical or electron microscopy).
v
The cobalt powders conventionally used in the cemented
~ carbide industry are obtained by calcining cobalt hy-
- droxide or oxalate followed by a reduction of the oxide
so obtained by hydrogen; see for instance "Cobalt, its
Chemistry, Metallurgy and uses", R.S. Young Ed. Reinhold
Publishing Corp. (1960) pages 58-59. These conventional
-. cobalt powders are characterised by a broad particle
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21~131
WO92/18656 3 PCT/SE92/Q0234
size distribution, with strongly aggregated particles,
in the form of agglomerates with a sponge-like aspect,
which are difficult to mill since there are strong
binding forces between the elementary particles in these
aggregates.
:
In EP-B-0113281, the making of metallic powders with a
process for reducing oxides, hydroxides or metal salts
~:. with the aid of polyols, is described. Particularly when
starting with cobalt hydroxide, it is possible to obtain
powders of metallic cobalt with essentially spherical
and non-agglomerated particles. Further studies have
shown in particular that it is possible to obtain non-
agglomerated metallic powders having controlled average
diameters of the particles, for instance by varying the
concentration of the starting hydroxide or metal salt,
in relation to the polyol(s). It is in this way that, in
the case of cobalt, it is possible to obtain particles
with an average diameter of, for instance 1, 2 or 3 ~m,
by using the ratios cobalt hydroxide/polyol of 0.033,
0.1 or 0.340 g cobalt/cm3 polyol, respectively. Simi-
larly, it is possible to obtain particles with adjust-
' able average dimensions, smaller than 1 ~m by seeding
the reaction mixture with the aid of very fine metallic
particles (for instance palladium) either by adding ametal salt or hydroxide reacting more quickly than the
; cobalt salt or hydroxide with the polyol. This is parti-
cularly the case with silver salts, in particular silver
nitrate, which are quickly reduced to metallic silver in
the form of very fine particles of which the number is
roughly proportional to the quantity of silver introduc-
ed into the reaction chamber. The silver or palladium
particles so formed serve as seed for the growth of co-
balt particles which are subsequently formed by reduc-
tion of the cobalt hydroxide or salt by the polyol. Thehigher the number of seed particles, the smaller the di-
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WO92/186S6 ~ 31 4 PCT/SE92/00234
mensions of the final cobalt particles. For instance,when using a molar ratio silver/cobalt in the range of
10-4-10-2, one can obtain cobalt particles having
average dimensions that vary from 0.1 to 0.3 ~m and the
s range can be extended by varying this ratio between 10-5
and lo-l for all the appropriate metals. These various
. methods for controlling the the size of the metallic
particles are particularly known and described by M.
FIGLARZ et al. M.R.S.Int'l Mtg on Adv. Mats. Vol 3, Ma-
terials Research Society, pp. 125-140 (1989), F.FIEVET
et al. Solid State Ionics 32/33, 198-205 (1989) and F.
FIEVET et al. MRS Bulletin, December 1989, pp.29-34.
It has now been discovered that the cobalt powders ha-
IS vins the properties of those obtained by the reduction
:: of cobalt hydroxide or a cobalt salt with the aid of po-
lyol, according to the EP-B-O 113 281 and the references
just mentioned, that is powders of individual, essenti-
ally spherical non-agglomerated particles, can be used
. 20 as binder phase powder in the manufacture of cemented
carbide and that this preparation gives several advanta-
. ges which are exposed below.
It has been particularly discovered that when using such
i 25 non-agglomerated cobalt powders, it is possible to ob-
;~ tain in a reproducible way, cemented carbide exhibiting
interesting characteristics, in particular, a reduced
porosity. It is also possible to decrease the milling
time for starting mixtures (carbide and binder) without
::`
impairing the quality of the final cemented carbide.
" Acceptable results can be obtained even after a simple
.~ blending operation. Alternatively, the degree of milling
;:~ may be further reduced and the cemented carbide
. subjected to a hot isostatic pressing process, either
~ 35 incorporated into the sintering process or as a separate
-, operation, giving an increase in the grain size of the
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210~31 5
W092/18656 PCT/SE92/00234
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hard phase and correspondingly an increase in resistance
to thermal cracking.
In addition, it has been discovered that, due to the use
S of such cobalt powders, it is possible to carry out the
; sintering at temperatures below those which are gene-
rally used. This decrease of sintering temperature is
interesting not only from an energy point of view, but
i also because it permits the possibility of adding to the
powder mixture other hard or superhard materials (in the
form of powders) which cannot normally be used at the
temperature required for conventional sintering. Among
. these other superhard materials, one can note particu-
- larly diamond, of which it is known that it starts
transforming into graphite in air at a temperature
, around 800 C and cubic boron nitride. Alternatively,
the sintering temperature may be lowered even further
;, and the cemented carbide subjected to a hot isostatic
pressing process, either incorporated into the sintering
process or as a separate operation, giving an increased
hardness level and a more uniform grain size and binder
phase distribution leading to an increase in mechanical
strength.
2s Generally, the cobalt particles used as binder phase ac-
cording to the invention have dimensions that can vary
from 0.1 to 20 ~m, in particular from 0.1 to 10 ~m. Par-
ticles having dimensions from 0.1 to 5 ~m are particu-
larly used. Especially interesting results have been ob-
tained with submicron particles ~that is with a size
-~ less than 1 ~m).
The present invention has thus as object the use - as
binder phase, in the preparation of cemented carbide by
3s milling, then sintering a mixture of powders with at le-
. ast one hard material based on tungsten carbide and a
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WO92/18656 21 ~ ~1 316 PCT/SE92/00234~ ~
binder phase - of at least one powder of cobalt, that is
homogeneous as regards the size of the particles, and
particularly one powder having an average particle size
x (in for instance the range O.l to 20 ~m, in particular
between O.l and lO ~m), of which at least 80~ of the
particles have sizes in the interval x +0.2x, provided
the interval of variation (that is 0.4x) is not smaller
than O.l ~m. The cobalt powder used in accordance with
the invention consists of individual, essentially sphe-
` 10 rical and nonagglomerated particles.
- Such powders can be especially obtained with the polyol
:
reduction which is recalled below. It is preferable to
start with cobalt hydroxide or cobalt acetate.
The cobalt powders obtained by the reduction of cobalt
hydroxide with the aid of polyol generally contain a
~- small proportion of carbon (most often less than l.5% by
weight) and oxygen (most often less than 2.5~ by
weight). These powders can be directly used in the manu-
. facture of cemented carbides.
Generally, according to the invention the cobalt powderused as binder in the preparation of cemented carbide
. 25 will exclusively be a powder such as defined above. But
it is possible to use such powders in combination with a
second cobalt powder exhibiting other characteristics,
provided the proportion of the first powder is suffici-
` ent for giving the advantages indicated in the prepara-
tion of cemented carbide, for instance a decrease of the
sintering temperature. Generally the first powder repre-
sents at least lO~, and preferably at least 50~ of the
- total weight of the cobalt used as binder phase.
In addition it is possible to use as binder phase a mix-
~, ture of two or more powders as defined above, these two
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;r~ W~ 92/18656 2 ~ 0 3 ~ 3 1 7 PCT/SE92/00234
..:
powders having different average particle dimensions.
It has also been found that the use of cobalt according
; to the invention is very suitable to adjust the binder
s content of an already dried cemented carbide mixture.
Such an adjustment is not possible with a conventional
-~ binder phase powder since the resulting mixture lacks
necessary flowability. Adding polyol cobalt does not
adversely affect flowability and can even improve it.
Thus, a unique ~mother-mix~ may be used for producing a
variety of cemented carbide grades having different
binder phase contents. After the addition of the polyol-
' cobalt, preferably with a particle size of <3 ~m, up to
the desired content the mixture is homogeneized before
lS pressing and sintering.
The starting powder mixture contains cobalt in suffici-
ent proportions for the final cemented carbide to con-
tain 0.1 to 40% by weight of cobalt, and preferably 3 to
; 20 25 %. It is particularly advantageous in grades with
very low contents of cobalt (typically <0.5%) often re-
ferred to as binderless grades.
Sintered cemented carbide bodies based on ~C, particu-
larly with a grain size <1.5 ~m, manufactured according
to the method of the invention has a porosity better
- than A02 and B00, less than 0.5, preferably less than
` 0.2, binder phase lakes per cm2 with a maximum dimension
of >25 ~m and less than five carbide grains per cm2 with
- 30 a grain size of more than 5 times the average grain size
~ of the matrix.
~ .
In the manufacture of cemented carbides where the sin~
tered grain size of the hard phases is fine, i.e. 1 ~m
}i 35 or less, it is commonplace to substitute a small amount
of other refractory metal carbides for tungsten carbide.
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WO92/18656 8 PCT/SE92/00234 ~
-` 210~131
The carbides commonly used are those of titanium, tanta-
- lum, niobium, vanadium, chromium and hafnium. The effect
of these substitutions is to control grain growth of the
hard phase during sintering. A side effect is that they
5 inhibit melt formation during sintering with the result
that often higher sintering temperatures are needed than
; would be the case without the substitution to ensure
; freedom from microporosity and a uniform binder phase
(cobalt-rich phase) distribution. The result is to
partly negate the advantage of the substitution, leading
to a degree of grain growth, recrystallization, of the
WC-phase which results in a nonuniform grain size dis-
tribution, a less than optimum hardness level and a re-
duction in mechanical strength. Using the cobalt-powder
according to the invention the above-mentioned grain
growth inhibitors may be excluded. This applies in par-
ticular to high pressure anvils for diamond production
in which the cobalt-content of the cemented carbide is
5-7 weight-% and WC grains size <1.5 ~m. Another example
: 20 is tools such as drills, microdrills and routers for ma-
chining of printed circuit boards and similar composite
materials. Such tools have a cobalt-content of 3-20
weight-%, preferably 4-12 weight-% and a WC grain size
of <1 ~m, preferably <0.7 ~m.
^. For certain applications where a degree of thermal shock
-~ is experienced, for example hot rolling of steel bar,
some mining and highway engineering applications and ma-
chining of stainless steel, it is desired that the hard
phases should be of relatively coarse grain size, typi-
. cally greater than 4 ~m preferably greater than 6 ~m and
the cobalt content <10, preferably <8 weight-%. A ce-
mented carbide powder to produce such a sintered hard
phase grain size must of necessity be relatively lightly
milled in order to control the degree of comminution.
~` The result is that the degree of intimate mixing is re-
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WO92~18656 9 210 8 ~ 31 PCT/SE92/00234
duced, and, owing to the coarse particle size, the area
available for reaction during sintering to produce a
melt is relatively small. Consequently, such cemented
carbide powders prove to be difficult to sinter and re-
quire high temperatures to approach a fully dense condi-
tion. Using the non-agglomerated, spherical cobalt pow-
der dense bodies can be obtained at a lower sintering
temperature.
In EP-A-0182759 it has been shown that an increased
strength was obtained in sintered bodies of cemented
carbide being used in tools for rock drilling. The but-
tons according to this patent has a core consisting of a
fine-grained eta-phase M6C (e.g. Co3W3C) and/or Ml2C
(e.g. Co6~6C), embedded in normal alpha (WC) and beta
(Co binder phase) structure at the same time as the sin-
tered body has a surrounding surface zone which consists
of alpha and beta-phase in two areas whereas the outer
shell is cobalt depleted and the inner part has a high
content of binder phase. Surprisingly it has now been
found that cemented carbide bodies manufactured in such
a way as described above give a more optimized toughness
behaviour when cobalt according to the invention is used
in the production of the buttons. The effect is most ut-
ilized for cemented carbide with a cobalt content ofmore than 10% and less than 25% by weight and preferably
13% to 20~ by weight of cobalt. The mean grain size of
the hard constituents is larger than l,5 ~m. The same
- appearance has also been obtained for cemented carbide
bodies with mean grain size of alpha-phase (WC) of less
than l,2 ~m and a binder content of e~ual or less than
6% by weight of cobalt. When cobalt according to the in-
vention is used in the sintering/heat treatment proce-
dure the sintering temperature can be reduced which re-
sults in a lower carbon content in the binder-phase and
a low porosity level. Ihe benefit of this sintering/heat
',
.~ .
:WO92/18656 ~ 10 81~ 1 lo PCT/SE92/00234 ^
:'~ ), .
treatment gives a product with a high carbon activity
:.and a fine grain size eta-phase which results in a ce-
mented carbide body with a more pronounced difference in
cobalt content in the surface zone between the outer co-
1s balt depleted shell and the inner part rich with cobalt.
:~The cemented carbide produced with the cobalt according
to the invention has a cobalt content with greater dif-
ference and reduced width of the shells in the surface
zone which leads to higher compressive stresses in the
surface zone and has also positive effects on strength
and toughness.
," "
The invention has been described above with reference to
the manufacture of conventional cemented carbide i.e.
based upon WC and with a binder phase of cobalt. It is
evident that the invention also can be applied to the
manufacture of articles of other composite materials
with hard constituents (borides, carbides, nitrides,
carbo-nitrides etc) and a binder phase, based on cobalt,
nickel and/or iron, such as titanium based carbonitride
alloys usually named cermets. Said alloys are manufactu-
red by milling powders of carbides, nitrides and/or car-
bonitrides of mainly Ti but also of other metals from
x~
.'groups VIa, Va and VIa of the periodical table of the
elements (V, Zr, Nb, Mo, Ta, W etc) together with pow-
ders of nickel and cobalt. The mixture is then dried,
pressed and sintered as described above for conventional
cemented carbide.
.~30 Example l
A suspension of cobalt hydroxide was put in a mixture of
.. ;.~ monoethylenglycol and diethylenglycol, while agitating.
::.'The suspension, containing about 200 g of cobalt hydrox-
ide per liter, was progressively heated to a temperature
of at least 200 C, while strongly agitating. A solution
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.
WO92/18656 ll 2 1 0 8 1 3 1 PCT~SE92/00234
of silver nitrate was then added in the monoethyleng-
lycol, so that between 0.07 and 0.3 g silver per liter
was introduced. The mixture was kept at the same tempe-
rature during 2 hours, and was then left to cool to room
5 temperature.
:'
In this way a cobalt powder (reference P1) was obtained
with the following properties:
- SEM diameter of the particles: 0.4 ~m
...... .
i 10 - C : 1.36% by weight
- O : 2.23% by weight
The SEM diameter is the average diameter of the par-
ticles measured in the scanning electron microscope.
In addition the following raw materials were used:
Tungsten carbide :
- Origin : Eurotungstène Poudres ~France)
- Total carbon : 6.15% by weight
- Free carbon : 0.05% by weight
. - Average diameter (Fisher) : 0.9 ~m
:
:l Tantalum carbide :
;i~ 2s - Origin : H.C.STARCK
~; - Total carbon : 6.81% by weight
~: - Free carbon : 0.10% by weight
~.:
- Niobium : 9.09% by weight
Cobalt (reference F) obtained by reduction of the oxide
. ,:~,.,
with hydrogen according to the conventional process:
- Origin : Eurotungstène Poudres
~, - Diameter according to Fisher : 1.30 ~m
- C : 0.012% by weight
With the aid of these materials the following mixtures
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W092/l8656 210 81 31 12 PCT/SE92/00234 ~-
were prepared:
- Cobalt: 3% or 6.5% by weight
. - Tantalum carbide: 0.5% by weight
- Tungsten carbide balance
; The powder mixture (500 g) was obtained by milling in a
mill of the type ~Attritor~ with a capacity of 9 liter,
., containing 3.5 kg of milling media (balls of cemented
carbide with a diameter of 3 mm) turning at 250
IO turns/minutes, in the presence of 200 ml of ethyl alco-
hol (or acetone) and with the addition of polyethylene
glycol (2 g per 100 g of mixture). The powder was milled
during 7 or 14 hours and thereafter granulated using a
; sieve with 120 ~m mesh size. The compaction was carried
out under uniaxial compaction from two directions, with
, matrix and punches of cemented carbide under a pressure
of 125 MPa. Sintering was performed at 1375, 1410 and
1450 C respectively. After sintering microsections were
prepared and the porosity and recrystallisation were de-
termined.
The porosity was determined according to the standard
ISO 4505 and is expressed with the aid of a scale of in-
creasing porosity from A00 to A08.
`.s The recrystallisation of tungsten carbide (or general
grain growth) was determined by microscopic examination
.:. and visual comparison with an internal standard scale
(analogous to that of the ISO scale for the porosity)
' 30 since no standard exists up to this day. The results are
;; expressed with a scale going from R1 ~quasi-absence of
-~..;;~ recrystallisation) to R5 (very strong recrystallisa-
~ tion).
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. WO92~18656 13 2 ~ 0 8 1 ~ ~ PcT/sE92/oo234
a) -Cobalt : 6.5~ by weight
-Milling : 14 hours
` -Sintering : 1450 C
.:; Results:
Type of cobalt P1 F
. Porosity A02 A03/04
Recrystallisation R2/R3 R4/R5
: b) -Cobalt : 6.5% by weight
-Milling : 7 hours
-Sintering : 1450 C
lS Results :
Type of cobalt P1 F
Porosity A02 A04
Recrystallisation R2 R2/R3
c) -Cobalt : 3% by weight
3 -Milling : 14 hours
-Sintering : 1375, 1410, or 1450 C
. -Results before HIP :
,
25 Results
Sintering temperature, C 1375 1410 1450
Type of cobalt P1 F P1 F P1 F
.~~ Porosity A02 A08 A02 A04 A02 A03
,. Cobalt lakes~ s N s N s N
* The average number of cobalt lakes was determined by
x~ counting (in an optical microscope) the lakes on ten op-
tical fields at a magnification of 1500 times and taking
``:. the average.
'~` s : a few
,`,!~. 35 N : Numerous
., .
':
WO92/18656 21~ 1 14 PCT/SE92/00234~.^
d) -Cobalt : 3~ by weight
-Milling : 14 hours
-Results after HIP
s The HIP treatment consists in putting the samples sin-
`. tered during the previous experiment in a HIP furnace at
1350 C, during 2 hours, under 100 MPa (atmosphere : ar-
gon).
Result :
.
Sintering temperature, C 1375 1410 1450
Type of cobalt Pl F Pl F Pl F
Porosity A01 A01 A01 A01 A01 A01
Cobalt lakes s N 0 N 0 N
IS s : a few
. N : numerous
Ss 0 : no
:~J
., These tests show clearly, that all other factors equal,
.:
;~ 20 the use of cobalt according to the present invention
, shows itself as beneficial in comparison with a
.~ conventional cobalt since it entails a decrease of
porosity and of the number of cobalt lakes.
~ ,,
;~ 25 xample 2
Two laboratory scale batches of cemented carbide powder
~ were made using the same batch of tungsten carbide, this
:,: batch having an average particle size of about 1 ~m as
measured by the Fisher sub-sieve sizer method. In grade
~ A 6% by weight of conventional hydrogen-reduced cobalt
;~ powder was added and in grade B 6% by weight of ultra-
:\, fine spherical cobalt powder was added. The same small
,'',,r' addition of chromium carbide powder was added to each
grade. A fairly intense degree of milling was given to
each grade by milling 1 kg of powder with 15 kg of mil-
.,
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~ 210~131
WO92/18656 l5 PCT/SE92/00234
. .~
ling bodies in a liquid for 13.5 hours in a rotary mill.
Compacts were made from the dried cemented carbide pow-
ders and sintered, in close proximity with each other,
under vacuum at a range of temperatures. Following sin-
- 5 tering, microsections were prepared and the porosity le-
vels were assessed by comparison with standard mi-
crographs according to method ISO 4505. The binder phase
distribution was assessed by an arbitrary method. The
specimens were first etched for 4 minutes at room tempe-
rature in Murakami's reagent and examined under an opti-
cal microscope at a magnification of l500X. The average
number of l~cobalt lakes~ present in a field of view was
assessed by counting the number observed in 10 fields
and dividing the total count by 10. Cobalt lakes are re-
gions of binder phase, typically from 2-10 ~m in diame-
ter, which occur when the sintering temperature was in-
adequate. The results obtained were as follows:
:,
Sintering Microporosity Co lakes
. 20 temperature, C per field
~i A 1450 A02 0
B 1450 A00 0
.~
~ A 1410 A02 4.9
s B 1410 A00 0
25 A 1360 A08 >200
B 1360 A02 5.6
From the above results it can be seen that the use of
ultrafine spherical cobalt powder in grade B had a
30 marked effect on the level of microporosity and binder
,~ phase distribution, especially apparent at the lowest
3 sintering temperature employed. As well as permitting a
lower sintering temperature to be employed, the use of
ultra-fine spherical cobalt powder confers an improved
s. 35 degree of tolerance to temperature variations within the
~- sintering furnace.
WO92/18656 2 1 V 8 1 ~ ~ PCT/SE92/00234~
Exampl,e_~
Two laboratory scale batches of cemented carbide powder
were made using the same batch of tungsten carbide. This
batch having a particle size of about 40 ~m according to
the Fisher subsieve sizer method. The true particle size
was however approximately 15 ~m, the higher Fisher value
being due to agglomeration. In grade C 6% by weight of
conventional cobalt powder was added and in grade D 6%
of ultra-fine spherical cobalt powder was added. No
other carbides were added. A 1 kg charge of cemented
carbide powder was milled with 5 kg of milling bodies
and a liquid for 13.5 hours in a rotary mill. Compacts
were made from the dried cemented carbide powders and
sintered, in close proximity to each other, under vacuum
at a ran~e of temperatures. Following sintering micro-
sections were prepared and the porosity levels assessed
according to the method detailed in ISO 4505. The re-
sults obtained were as follows:
, .
~ Grade Sintering Microporosity
',~ temperature, C
C 1520 A02
,, 25 D 1520 A00
'"' C 1450 A06
, D 1450 A02
~, C 1410 A08
; D 1410 A02
" 30 C 1360 >A08
' D 1360 A06
,
The above results illustrate that using ultra-fine sphe-
rical cobalt powder a marked reduction in porosity le-
vels was achieved. Thus, lower sintering temperaturesmay be employed and again an improved degree of tole-
';
, .
.~ .
W092/t8656 2 1~ ~ 13 ~ 17 PCT/SE92/00234
.f. '.:
.:,
rance to temperature variation within a furnace change
is conferred.
Exam~le 4
S
Anvils for the 60 mm diamond production system have been
; tested according to the performance represented as life
length in a diamond production. The anvils were manu-
factured in three different grades of cemented carbide
10 and marked with random numbers prior to the testing. The
performance test was applied in a diamond production
plant during "normal'~ working conditions whereas the re-
-~ sults were reported with life lengths in compa-ison to
presently used anvils. All anvils have a core consisting
15 of a small amount (2~) of eta-phase in the structure.
,;
, .,
,. The anvils of grade A were manufactured according to the
conventional production route of cemented carbide and
s were used as a reference in the test. The anvils were
20 produced as described in example 1 with 6% by weight of
conventional hydrogen-reduced cobalt and a small addi-
tion of chromium carbide. The sintering temperature was
1450 C and the cemented carbide had a microporosity of
;; A02. The microstructure did not show any cobalt lakes.
The anvils of grade B had a similar composition as des-
`,t, cribed for anvils of grade A without the chromium car-
;:~ bide content. The anvils were subjected to a hot isosta-
tic press~ng process at 4 MPa and 1410 C instead of
. 30 standard sintering. No microporosity was obtained in the
, .
microstructure and 5,2 cobalt lakes per field were pre-
;~ sented from microscopic examination of the cemented car-
, bide. The microstructure was even and no influence of
discontinuous or local grain growth could be seen.
The anvils of grade C had a composition according to the
: ,
~'~ "
. .. ~ . . ... .
. ,
~,~,. $~ .
.~ .
. . .
~1~8131
WO92/18656 18 PCTtSE92/00234.~
invention as described in Example 2 without the chromium
: carbide content. The anvils were subjected to a hot iso-
static pressing procedure with the same conditions as
for the anvils of grade B. The microstructure examina-
tion of the cemented carbide did not show any microporo-
sity (A00) or cobalt lakes. The structure was even
without any influence of discontinuous grain growth.
The ~-phase (WC) in the microstructure of the three gra-
des of anvils had a mean grain size of about 1,2 ~m.
.... .
The performance results were reported in actual number
, of pressings per anvil and scaled in a performance ran-
.' king. Each cemented carbide grade was represented by six
, .
l5 anvils.
.
;:
;,.j Results: Anvil No Number of Performance/Rank
~ pressings
,.~ Grade A: 1 299 D
~; 20 2 99 E
3 50 F
~ ,:
4 921 A
~i,.' 5 384 C
,~,
~ 6 50 F
., . _
Average 300 C
'"~
Grade B: 1 568 C
-~.i 2 289 D
3 270 D
4 580 C
602 B
6 430 C
Average 456 C
..~.
, , .
., .
:'' .
.,.:
. . .
.,.
WO92/18656 2 ~ 9 : PCT/SE92/00234
Grade C: 1 702 (still in use)B
2 1399 A
3 608 B
4 592 C
820 B
6 906 A
Average 837 B
The results of grade A were uneven and the anvils with
the low numbers of pressings had cracks in the top of
the anvils. Grade B had a better performance but got the
same ranking level as grade A. Three anvils had small
cracks in the top surface. Grade C had the best perfor-
` l5 mance ranking in the test and the best pressing beha-
viour of all anvils. Obviously the anvils according to
;- the invention had the most optimized hardness and tough-
. ness behaviour due to a well dispersed cemented carbide
matrix and a narrow grain size distribution of ~-phase.
, .
:. 20
.~ Exam,l; 1e 5
,,~
A coarse grained tungsten carbide with a grain size of
.~:
18 ~m was in the as supplied state used to produce test
batches of very coarse cemented carbide for concrete and
asphalt cutting tools. Cemented carbide with low cobalt
''"~'J, content and very coarse grain size is needed to achieve
;i optimum combination of toughness to wear resistance pro-
perties together with maximum thermal fatigue crack re-
sistance.
The same procedure as in Example 3 was used except for
that the milling time was reduced to 9,5 hours.
Grade X was produced with 6% of conventional cobalt and
grade Y with 0.3 ~m of ultrafine spherical cobalt pow-
~'
. .
:
.: .:. .
. .
W092/18656 ~1 V ~l 31 20 PCT/~E92/00234~.
der. Sintering was performed at 1520 C in vacuum. GradeX showed a porosity level of A06, B06 plus 8 pores of 25
~m, and had to be HIP'ed. Grade Y was fully dense with
maximum porosity of A02, due to the effective and uni-
s form reduction of the WC-grains together with excellent
mixing of the spherical cobalt with the tungsten carbide
grains.
~,.
j The metallographical analysis showed as follows:
: 10
Grade X ~ Grade Y
~: Grain size mean value 7 + 4 ~m 7 + 1,5 ~m
maximum size 18 ~m 10 ~m
.: minimum size 1.8 ~m 5 ~m
: 15 structure: uneven with 10-15 even
cobalt lakes of 10-20 ~m
hardness, (HV3): 1215 1205
.,
:i, Road planing tips were made from the two test batches
and were compared with a conventional grade, Z with 8
.~ w/o Co, 5 ~m WC grains and a hardness of 1200 HV3. Point
attack tools from the three grades were made, and they
were geometrically identical with the carbide tips (09
. mm, length 18 mm with a conical top) brazed at the same
;~l 25 time.
~, The test was made in hard concrete with an Arrow CP 2000
- road planing machine.
Drum diameter: 1 m, drum widthi 2.2 m
- Toolpick speed: 2.0 m/s, cutting depth: 25 mm
180 tools, 60 per grade, were evenly distributed
throughout the drum.
,i
;
WO92/18656 210 3131 21 PCT/SE92/00234
Test result (mean value of 50 tools)
Grade Wear, Fractured Rank
mm height carbide
reduction (no of pieces)
X 5,3 8 2
Y ~,8
Z 8,1 7 3
lO Exam~le 6
. . ,
. Buttons for roller bits with diameter 12 mm having a
: multiphase structure were produced from a small produc-
tion batch. The average particle size of the WC was 3.5
15 ~m and the nominal cobalt content was 13.5% by weight.
The added cobalt was ultra-fine spherical cobalt powder
with a Fisher grain size of 0.3 ~m. Compacts of the ce-
mented carbide powder were sintered at 1340C. Corre-
.~ sponding buttons were produced with the same production
~ 20 process parameters except of the sintering temperature
- which was 1380C. These buttons originating from a ce-
s mented carbide powder blending with conventional cobalt
~;3 powder with a Fisher grain size of 1.4 ~m. All buttons
were thermally treated in a carburizing atmosphere for 2
25 hours. In the following examination of the microstruc-
ture of buttons from the two batches it could be seen a
multiphase structure with a core that contained eta-
phase surrounded by a surface zone of cemented carbide
free of eta-phase having a low content of cobalt at the
30 surface and a higher content of cobalt next to the eta-
phase "core".
Microprobe studies of the microsections gave the follo-
wing results:
~ ~ .
21~)8131
WO92/18656 22 PCT/SE92/00234
Grade A (with ultra-fine cobalt):
Etaphase core (05.0 mm):
` mean grain size of etaphase: 4,l ~m
~, s mean cobalt content: ll.5 weight-%
:, Cobalt "rich" zone (width l,5 mm)
mean cobalt content: 14.2 weight-%
,.~.!,, Cobalt l'depletedl~ zone (width 2.0 mm)
.,, mean cobalt content: lO.0 weight-%
~ 1 0
~ Gra,d,,e_B (according to prior art with conventional co-
---, balt)
Eta phase core (07.0 mm):
mean grain size of eta-phase: 4,8 ~m
: 15 mean cobalt content: ll.5 weight-%
:
,'.",r; Cobalt "rich" zone (width l mm)
~, mean cobalt content: 15.3 weight-%
. Cobalt ~depleted~ zone (width l,5 mm)
, ",~ mean cobalt content: 8.7 weight-%
No porosity could be seen in the surface zone. It is ob-
vious that buttons prepared according to the invention
,, gave a more distinct multi-phase structure with a higher
cobalt-gradient in the surface zone.
,. 25
,Exam~le 7
Wear and toughness tests were performed with roller bits
in an open-cut copper mine. The roller bits were of type
9 7/8" CS consisting of three roller cones with spheri-
" : 1
cal buttons. The diameter of the buttons was 12 mm. For
.: .
. one roller bit the buttons accordang to the invention
,, were placed in all positions of the buttons in row l.
.,. Three types of roller bits were used in the test.
Bit A Buttons according to Example 6 were placed as
~ ,^,t~.',
,~.
. .
WO92/18656 210 ~131 23 PCT/SE92/00234
. .
above and in the excepted positions comparative
buttons with the same composition according to
prior art.
Bit B Comparative buttons of Example 6 according to
prior art in all positions.
,~
Bit C Standard cemented carbide with the same composi-
tion as in Example 6 but being free of eta-phase
: lO and without the multi-phase structure.
Drill rig: 1 pce. BE 45R
Feed: 0-60000 lbs
Rpm: 60-85
Hole depth: 18-20 m
~;~ Type of rock: Biotite gneiss, mica schist.
:
. Results:
Grade drilled meters index drilling index
depth (m/h)
A 1900 160 18 140
B 1650 140 16 120 prior art
. C 1170 100 13 100 prior art
The grade according to the invention has obtained longer
life length as well as greater drilling rate.
:
The wear of the buttons was measured at 800 drilled me-
ters.
Results
Grade A: Row 1: Buttons according to the invention
Average wear 3.0 mm
Row 2: Average wear 2.8 mm
Row 3: Average wear 2.5 mm
s ,
.
~108131
WO 92tl8656 24 PCT/SE92/00234
The wear profile gave a self-sharpening effect due to a
wear looking like ~egg shells'~. This effect was most
marked at row l. One button was missing in row 1.
Grade B: Row 1: Average wear 3.2 mm
Row 2: Average wear 2.8 mm
;. Row 3: Average wear 2.4 mm
~.
~` The wear of the buttons was of "egg shells"-type. From
row 1 three buttons from one roller cone and two respec-
; tively one from the other two were missing. Two buttons
- were missing in row 2.
: ~,
; Grade C: Row 1: Average wear 3.6 mm
Row 2: Average wear 3.0 mm
, - Row 3: Average wear 2.6 mm
`' From row 1 five buttons from one roller cone and four
: respectively one from the other two were missing. The
. penetration rate was slow at 800 drilled meters.
` 20
This test gave surprisingly good results for the roller
bit attached with buttons made according to the inven-
tion. The penetration of the roller bit was also very
good.
; 2S
~ Exam~le 8
~:,
From a 91.5 : 8.5 WC(2 ~m)/Co(1.2 ~m) powder mixture,
granules (hereafter referred to as basic granules) were
prepared according to the conventional technique. Then a
:` sufficient amount of cobalt (polyol-type 1 ~m) was added
to the granules until the respective proportions of
; WC/Co reached 88:12. After mixing for 30 minutes in a
Turbula-type mixer, the resulting mixture (Imodified
granules') was tested for flowability according to ISO
4490 with the following results:
:, .
: .
wo 92/18656 2 1 0 8 1 3 1 2s PCT/SE92/00234
, . . ~, , .
,.
Time/100 g, s
; Basic granules 53
~ Modified granules 46
-~: 5
~- After compaction and sintering a cemented carbide was
. prepared with the basic granules and the modified granu-
les. The Vickers hardness was determined with the follo-
wing result:
:' 10
: ~V50
Basic granules 1455
^i Modified granules 1300
.. ...
: l5 As expected the hardness of the cemented carbide with
the modified granules was lower than that of the basic
.; cemented carbide in view of the higher cobalt content.
The structure of the carbide obtained with the modified
granules was satisfactory.
;~, .
~ ~"
:. .
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: - ' : : :
, .
