TECHNICAL FIELD
[0001] The present disclosure relates to a method of redistributing the binder within a
cemented carbide mining insert, a cemented carbide mining insert with a hardness gradient
and the use thereof.
BACKGROUND
[0002] Cemented carbide has a unique combination of high elastic modulus, high hardness,
high compressive strength, high wear and abrasion resistance with a good level of
toughness. Therefore, cemented carbide is commonly used in products such as mining
tools. In general, the hardness and toughness of cemented carbide can be altered by
changing the binder content and grain size of the hard phase. Typically, a higher
binder content will increase the toughness of the cemented carbide but will decrease
its hardness and wear resistance. A finer hard phase grain size will result in cemented
carbide with a higher hardness which is more wear resistant, whereas a coarser hard
phase grain size will not be as hard but will have higher impact resistance.
[0003] For maximised efficiency of cemented carbides mining inserts, a combination of these
properties is desired and there are different demands on the material in different
parts of the product. For example, in inserts for rock drilling and mineral cutting,
it is desirable to have a tougher interior to minimize the risk of failure and a harder
exterior to optimise wear resistance.
[0004] WO 2010/056191 discloses a method of forming a cemented carbide body comprising a hard phase and
a binder phase, wherein at least one part of the intermediate surface zone has lower
average binder content than a part further into the body.
[0005] There is however still a need for a method which is able to create even greater hardness
gradients, able to tailor the gradient to a specific application and which could be
applied even to non-symmetrical cemented carbide mining inserts. There is also a need
to for a method which can redistribute the binder phase starting with a standard carbide
powder which is stoichiometrically balanced with respect to carbon content.
SUMMARY
[0006] Thus, the present disclosure therefore provides a method of redistributing the binder
phase within a cemented carbide mining insert comprising one or more hard-phase components
and a binder comprising the steps of:
- a) providing a green cemented carbide mining insert;
- b) applying at least one binder puller selected from a metal oxide or a metal carbonate
to the surface of the green cemented carbide mining insert; and
- c) sintering the green cemented carbide mining insert;
characterized in that the metal oxide or metal carbonate is only applied to at least
one local area on the surface of the green cemented carbide mining insert.
[0007] This method allows the binder to be re-distributed in a tailored and most favourable
manner to provide optimal functionality to the cemented carbide mining insert. For
examples, specific hardness profiles can be created for different application.
[0008] Additionally, the present disclosure relates a cemented carbide mining insert comprising
one or more hard-phase components and a binder characterized in that there is a hardness
gradient from a first part of the surface to a second part of the surface of the cemented
carbide mining insert, wherein the first part of the surface is substantially opposing
the second part of the surface, such that:
- the first part of the surface is between 30HV3 softer and 80HV3 harder than the second
part of the surface; and
- the first part of the surface is between 5 and 120 HV3 harder than the bulk; and
- the second part of the surface is between 20HV3 and 70HV3 harder than the bulk.
FIGURES
[0009]
Figure 1: Schematic drawing of an insert showing the binder puller and binder pusher
applied symmetrically to opposing sides.
Figure 2: Schematic drawing of an insert showing the binder puller and binder pusher
applied asymmetrically to opposing sides.
Figure 3: HV3 iso-hardness plots for sample A disclosed in example 1.
Figure 4: HV3 iso-hardness plots for sample B disclosed in example 1.
Figure 5: HV3 iso-hardness plots for sample C disclosed in example 1.
Figure 6: HV3 iso-hardness plots for sample D disclosed in example 1.
Figure 7: HV3 iso-hardness plots for sample E disclosed in example 1.
Figure 8: HV3 iso-hardness plots for sample F disclosed in example 1.
Figure 9: HV3 iso-hardness plots for sample G disclosed in example 1.
Figure 10: HV3 iso-hardness plots for sample H disclosed in example 1.
Figure 11: HV3 iso-hardness plots for sample I disclosed in example 1.
Figure 12: HV3 iso-hardness plots for sample J disclosed in example 1.
Figure 13: HV3 iso-hardness plots for sample K disclosed in example 1.
Figure 14: Schematic drawing of an insert showing where the binder puller was applied
in example 1.
Figure 15: HV3 centre line hardness profiles for samples A, B and C disclosed in example
1.
Figure 16: HV3 centre line hardness profiles for samples D, E and F disclosed in example
1.
Figure 17: HV3 centre line hardness profiles for samples G, H and I disclosed in example
1.
Figure 18: HV3 centre line hardness profiles for samples J and K disclosed in example
1.
Figure 19: HV5 iso-hardness plots for example 2 wherein the binder puller and binder
pusher are applied asymmetrically.
Figure 20: Schematic drawing of the set up for the pendulum hammer test.
Figure 21: Cobalt concentration profiles as discussed in example 5 for samples D and
G.
Figure 22: Chromium concentration profiles as discussed in example 5 for samples D
and G.
Figure 23: Cr/Co concentration profiles as discussed in example 5 for samples D and
G.
Figure 24: Cobalt concentration profiles as discussed in example 5 for sample K.
Figure 25: Chromium concentration profiles as discussed in example 5 for sample K.
DETAILED DESCRIPTION
[0010] According to one aspect, the present disclosure relates to a method of redistributing
the binder phase of a cemented carbide mining insert comprising a WC hard-phase, optionally
one or more further hard-phase components and a binder comprising the steps of:
- a) providing a green cemented carbide mining insert;
- b) applying at least one binder puller selected from a metal oxide or a metal carbonate
to the surface of the green cemented carbide mining insert; and
- c) sintering the green cemented carbide mining insert;
characterized in that the metal oxide or metal carbonate is only applied to at least
one local area on the surface of the green cemented carbide mining insert.
[0011] The one or more further hard-phase components may be selected from TaC, TiC, TiN,
TiCN, NbC, CrC. The binder phase may be selected from Co, Ni, Fe or a mixture thereof,
preferably Co and / or Ni, most preferable Co. The carbide mining insert has a suitable
binder content of from about 4 to about 30 wt%, preferably from about 5 to about 15
wt%. The carbide mining insert may optionally also comprise a grain refiner compound
in an amount of ≤20 wt% of the binder content. The grain refiner compound is suitably
selected from the group of carbides, mixed carbides, carbonitrides or nitrides of
vanadium, chromium, tantalum and niobium. With the remainder of the carbide mining
insert being made up of the one or more hard-phase components.
[0012] In one embodiment of the method, the cemented carbide mining insert contains a hard
phase comprising at least 80 wt% WC, preferably at least 90 wt%.
[0013] In the present disclosure, the term "green" refers to a cemented carbide mining insert
produced by milling the hard phase component(s) and the binder together and then pressing
the milled powder to form a compact cemented carbide mining insert, which has not
yet been sintered. The term "binder puller" refers to a substance which when applied
to the surface of the cemented carbide mining insert will cause the binder to migrate
towards that surface during the sintering step, i.e. the binder is pulled in the direction
towards the surface where the "binder puller" has been applied. The binder puller
works by locally consuming carbon which causes the binder to flow from the areas having
normal carbon levels to the local area where the carbon level has been depleted.
[0014] The inventors have found that applying the binder puller, which is selected from
a metal oxide or a metal carbonate, to the surface of the green cemented carbide mining
insert in at least one local area, that carbon is locally consumed in this area during
sintering which causes the formation of a carbon potential. This will promote the
migration of the binder phase from areas having normal or higher levels of carbon
to the local area which has a depleted carbon level. This will therefore form a binder
rich region on a local area of the surface of the cemented carbide mining insert.
The surface of the green cemented carbide mining insert where the binder puller is
applied is referred to as the "oxide / carbonate doped" surface. It is well known
that binder rich regions and binder depleted regions will be in tensile stress and
compressive stress respectively after sintering. It would normally not be favourable
to introduce tensile stresses. However, the inventors have found that after a treatment,
such as centrifugal tumbling, high levels of compressive stress, down to at least
1mm depth below tumbled surface, can be introduced to counteract the tensile stresses
present. Therefore, the benefit of applying the binder puller can be gained without
the detrimental effect of introducing tensile stresses.
[0015] The "at least one local area on the surface of the green cemented carbide mining
insert" could be at any position on the surface, for example the tip, the base or
the side depending on where the requirement to create an increase in binder content
is. The binder puller may be applied to one or more local areas on the surface of
the cemented carbide mining insert depending on whether the desired effect is to create
a local increase in toughness or wear resistance. Each "local area" may be 0.5-85%
of the total surface area of the cemented carbide mining insert, preferably 3-75%.
[0016] The sintering temperature is suitably from about 1000°C to about 1700°C, preferably
from about 1200°C to about 1600°C, most preferably from about 1300°C to about 1550°C.
The sintering time is suitably from about 15 minutes to about 5 hours, preferably
from about 30 minutes to about 2 hours.
[0017] In one embodiment of the method, the binder puller, being a metal oxide or metal
carbonate is selected from Cr
2O
3, MnO, MnO
2, MoO
2, Fe-oxides, NiO, NbO
2, V
2O
3, MnCO
3, FeCO
3, CoCO
3, NiCO
3, CuCO
3 or Ag
2CO
3. It would also be possible to alternatively apply a metal to the surface of the green
cemented carbide mining insert which upon heating, during the sintering step, would
form an oxide. The selection of the metal oxide or metal carbonate will influence
the properties of the cemented carbide post sintering e.g. deformation hardening,
heat resistance and / or corrosion resistance and the selection can be made to be
best suited to the required application. Metal carbonates would be selected if the
equivalent metal oxide is toxic and the metal carbonate is not. In this method, there
is a high degree of freedom as to where the binder puller is applied, for example
it could be applied in or away from the wear zones of the carbide tool, depending
on whether the metal in the oxide or carbonate improves the wear resistance of the
cemented carbide or not.
[0018] In one embodiment of the method, the binder puller is Cr
2O
3. Using Cr
2O
3 as the binder puller has the advantage that a chromium alloy rich surface layer will
form, which has an enhanced response to a tumbling treatment. Therefore, higher compressive
stresses will be introduced, and the wear properties of the cemented carbide mining
insert will be improved. The Cr
3O
2 contributes towards grain refinement and hence, a reduced grain size is measured
on the side of the insert where the Cr
3O
2 has been applied.
[0019] The metal oxide or metal carbonate is suitably provided onto the surface or surfaces
in an amount of from about 0.1 to about 100 mg/cm
2, preferably in an amount of from about 1 to about 50 mg/cm
2. The starting cemented carbide powder blend should suitably have a carbon balance
equivalent to 0.95<Com/%Co<1 or have an excess of carbon that would compensate for
the carbon reduction from the application of the oxide or carbonate. Com is 100*S,
Insert/σ
S, Cobalt wherein σ
S is the weight specific saturation magnetization measured in Tm
3/kg and σ
S, Cobalt = 2.01E-4 Tm
3/kg. Com is measured in a Foerster Koerzimat CS.1097 unit.
[0020] In one embodiment of the method, the binder puller is applied to the top of the cemented
carbide mining insert. In another embodiment of the method, the binder puller is applied
to the side of the cemented carbide mining insert. Therefore, the properties of the
cemented carbide mining insert can be tailored to be suited to the application. The
binder puller is likely chosen to be applied to the position on the surface of the
cemented carbide mining insert that is exposed to the highest wear.
[0021] In one embodiment, the method further comprises the step between steps a) and b)
of applying at least one binder pusher to at least one different local area on the
surface of the green cemented carbide mining insert. In the present disclosure, the
term "binder pusher" refers to a substance, which when is applied to the surface of
the carbide mining insert, will cause the binder to migrate away from that surface
during the sintering step, i.e. the binder is pushed in the direction away from the
surface where the "binder pusher" has been applied. The combined application of a
binder puller applied to at least one local area on the surface and a binder pusher
to the at least one different local area on the surface of the cemented carbide mining
insert would mean that the green cemented carbide mining insert could be made having
a carbon content within the standardly used ranges, such as 0.95<Com/%Co<1, and using
standard processes therefore allowing for efficiency in the production. Preferably
the migration takes places through the depth of the insert, rather than along the
surface of the insert.
[0022] In one embodiment of the method the binder pusher is selected from a metal carbide,
a carbon powder, such as graphite, or a mixture thereof. The application of the metal
carbide, the carbon powder or the mixture thereof will create a carbon gradient, which
will result in the cobalt migrating away from the surface to which it was applied,
i.e. the binder is pushed away from that surface of the carbide towards the inner
bulk in this local area(s). Selection of a metal carbide will have the additional
effect of grain refinement in the applied local area whereas the selection of a carbon
powder will have the effect of promoting grain growth in the applied local area(s).
The resulting difference in the grain growth gradient created is not as significant
as the effect that the binder gradient has on the hardness gradient.
[0023] In one embodiment, the binder pusher is a combination of a metal carbide and a carbon
powder. The weight ratio of the metal carbide to the carbon powder is suitable from
about 0.05 to about 50, preferably from about 0.1 to about 25, more preferably from
about 0.2 to about 15 and even more preferably from about 0.3 to about 12 and most
preferably from about 0.5 to 8. The metal carbide is suitably provided onto the surface
or surfaces in an amount of from about 0.1 to about 100 mg/cm
2, preferably in an amount of from about 1 to about 50 mg/cm
2. The carbon powder is suitably provided onto the surface or surfaces in an amount
of from about 0.1 to about 100 mg/cm
2, preferably in an amount of from about 0.5 to about 50 mg/cm
2.
[0024] If only a carbon powder, such as graphite, is selected as the binder pusher this
would lead to a coarsening of the hard phase grains in the area where it has been
applied. This would result in being able to achieve a combination of high wear resistance
and improved thermal conductivity in the zones on the mining button exposed to the
rock being worked and high toughness behind these zones.
[0025] In one embodiment of the method the metal carbide is selected from a carbide of chromium,
vanadium, magnesium, iron or nickel, preferably a carbide of chromium, such as Cr
3C
2, Cr
23C
6, Cr
7C
3.
[0026] Selection of a metal carbide, such as Cr
3C
2, in combination with a carbon powder is advantageous as this combination will cause
the binder to migrate from the doped surface and the addition of the carbon prevents
the grain refining effect of the Cr
3C
2.
[0027] During sintering any metal carbide applied to the surface of the green cemented carbide
mining insert should substantially dissolve.
[0028] In one embodiment of the method, the binder puller and the binder pusher are applied
to different local areas of the surface of the cemented carbide mining insert. By
applying the binder puller and binder pusher to different local areas a binder gradient
between the two surfaces is created. This gradient in binder will mean that a hardness
gradient is created, with a harder, binder depleted surface formed where the binder
pusher has been applied and a tougher, binder rich surface formed where the binder
puller has been applied. The combined application of a binder puller and binder pusher
to different local areas of the surface of the cemented carbide mining insert is particularly
useful in creating a hardness gradient in larger carbide bodies where previously known
methods would not create a sufficiently deep gradient. The binder puller may be applied
to a selected area on the surface of the green cemented carbide mining insert and
the binder pusher may be applied to a different selected area on the surface of the
green cemented carbide mining insert. The binder pusher could be placed in the wear
zone to reduce the binder content and therefore improve wear resistance in that area
or where it is favourable to have higher thermal conductivity. The local application
of the binder puller and the binder pusher presents unique possibilities to create
carbide bodies with tailor made properties.
[0029] Another benefit of using this method is that self-sharpening zones can be created
if the wear rates on different areas of the surface are uneven. The contact pressure
between a worn insert and the rock increases with a sharper tip as there is a reduced
area of contact. With a homogenous material, the wear causes the formation of a wear
flat that often needs re-sharping using diamond grinding tools. Re-sharpening by grinding
is costly and requires that the drill bits are unmounted. By having non-homogeneous
material properties, it is possible to have zones that wear faster and zones that
wear slower. If the material properties of the mining inserts are tailored to having
a wear surface that has areas with different wear rates, the formation of wear flats
are avoided, and consequently sharper wear surfaces are created in comparison to using
homogeneous materials.
[0030] In one embodiment of the method, the binder puller and the binder pusher are applied
to substantially opposing local areas of the surface of the cemented carbide mining
insert.
[0031] In one embodiment, the method of applying the binder puller and the binder pusher
is selected from pressing, dipping, painting, spraying (air brushing), stamping or
3D printing. Dipping could be done with or without masking. The binder puller and
binder pusher may be applied to the surface of green cemented carbide mining insert
in the form of liquid dispersions or a slurry. In such as case, the liquid phase is
suitably water, an alcohol or a polymer such as polyethylene glycol. The concentration
of the slurry is suitably 5-50 wt% of the powder in the liquid phase, such as 15-40
wt%. This range is advantageous so that a sufficient effect of the binder puller or
pusher is realised. If the powder content is too high, then there may be issues with
clogging and lumping within the liquid dispersion or slurry. Alternatively, they could
be introduced as a solid substance, for example by adding the powder into the pressing
mould in a suitable position. The powder could be mixed with a hard-phase powder,
for example a WC-based powder. The binder puller and the binder pusher could also
be applied to the cemented carbide mining insert in any other suitable way. The compositions
and concentration of the slurry and the way it is applied influences the control of
the redistribution of the binder and therefore allows the hardness profile of the
cemented carbide mining insert to be controlled.
[0032] In one embodiment of the method, the binder puller is applied to a first part of
the surface (10) and the binder pusher is applied to a second part of the surface
(20) rotationally symmetrically as shown in Figure 1.
[0033] In one embodiment of the method, the binder puller is applied to a first part of
the surface (10) and the binder pusher is applied to a second part of the surface
(20) rotationally asymmetrically as shown in Figure 2.
[0034] As there is flexibility in where the binder puller and binder pusher are applied,
this allows tailoring of the position of the "wear zone", i.e. the position on the
surface having the most enhanced wear properties. For example, the wear zone could
be on either the top or the side of the insert depending where the interaction between
the cemented carbide mining insert and rock being drilled is the highest. This will
vary depending on the application it is being used for and the position of the cemented
carbide mining insert on the rock drill bit.
[0035] Cemented carbide mining inserts are subjected to high compressive loading. Consequently,
surface cracking caused by small cracks growing to a critical size through repeated
intermittent high loading is a common cause of insert failure. It is known that introducing
compressive stress into the surface of the insert can reduce this problem as the presence
of the compressive stress can prevent crack growth and wear of the material. Known
methods of introducing compressive stress into surfaces of a cemented carbide mining
insert include shot peening, vibration tumbling and centrifugal tumbling. These methods
are all based on mechanical impact or deformation of the outer surface of the body
and will increase the lifetime of the cemented carbide mining inserts.
[0036] In one embodiment of the method, post sintering the cemented carbide mining insert
is treated with a tumbling process. The cemented carbide mining inserts are subjected
to a posttreatment surface hardening which introduces high levels of compressive stress
into the inserts. For mining inserts, this would normally be a tumbling treatment,
which could be centrifugal or vibrational. However, other post-treatments surface
hardening methods, e.g. shot peening, could be used. Following tumbling, normally
an increase in magnetic coercivity (kA/m) is measured.
[0037] A "standard" tumbling process would typically be done using a vibrational tumbler,
such as a Reni Cirillo RC 650, where about 30 kg inserts would be tumbled at 50 Hz
for about 40 minutes. An alternative typical "standard" tumbling process would be
using a centrifugal tumbler such as the ERBA-120 having a closed lid at the top and
has a rotating disc at the bottom. Cooling water with antioxidants is continuously
fed with 5 liters per minute when the disc (Ø600mm) rotates. Tungsten carbide media
can also be added to increase the load in the tumbler. The rotation causes the inserts
to collide with other inserts or with any media added. The collision and sliding removes
sharp edges and causes strain hardening. For "standard" tumbling using a centrifugal
tumbler the tumbling operation would typically be run from 120 RPM for at least 20
minutes.
[0038] In one embodiment of the method, the tumbling process is a "High Energy Tumbling"
(HET) method. To introduce higher levels of compressive stresses into the cemented
carbide mining insert a high energy tumbling process may be used. There are many different
possible process set ups that could be used to introduce HET, including the type of
tumbler, the volume of media added (if any), the treatment time and the process set
up, e.g. RPM for a centrifugal tumbler etc. Therefore, the most appropriate way to
define HET is in terms of "any process set up that introduces a specific degree of
deformation hardening in a homogenous cemented carbide mining insert". In the present
disclosure, HET is defined as a tumbling treatment that would introduce a hardness
change, measured using HV3, after tumbling (ΔHV3%) of at least:
Wherein:
[0039] HV3
bulk is an average of at least 30 indentations points measured in the innermost (centre)
of the cemented carbide mining insert and HV3
0.3mm is an average of at least 30 indentation points at 0.3mm below the tumbled surface
of the cemented carbide mining insert. This is based on the measurements being made
on a cemented carbide mining insert having homogenous properties. By "homogeneous
properties" we mean that post sintering the hardness different is no more than 1%
from the surface zone to the bulk zone. The tumbling parameters used to achieve the
deformation hardening described in equations (1) and (2) on a homogenous cemented
carbide mining insert would be applied to cemented carbide bodies having a gradient
property.
[0040] HET tumbling may typically be performed using an ERBA 120, having a disc size of
about 600 mm, run at about 150 RPM if the tumbling operation is either performed without
media or with media that is larger in size than the inserts being tumbled, or at about
200 RPM if the media used is smaller in size than the inserts being tumbled; Using
a Rösler tumbler, having a disc size of about 350 mm, at about 200 RPM if the tumbling
operation is either performed without media or with media that is larger in size than
the inserts being tumbled, or at about 280 RPM if the media used is smaller in size
than the inserts being tumbled. Typically, the parts are tumbled for at least 40-60
minutes. HET enables use of binder enriched surface zones as the compressive stresses
introduced from the HET counteract the tensile stresses formed by the higher thermal
expansion coefficient in the binder enriched zones adjacent to binder depleted zones.
[0041] Another aspect of the present invention relates to a cemented carbide mining insert
comprising one or more hard-phase components and a binder wherein there is a hardness
gradient from a first part of the surface to a second part of the surface of the cemented
carbide mining insert, wherein the first part of the surface is substantially opposing
the second part of the surface, such that post sintering:
- the first part of the surface is between 30HV3 softer and 80HV3 harder than the second
part of the surface; and
- the first part of the surface is between 5 and 120 HV3 harder than the bulk; and
- the second part of the surface is between 20HV3 and 70HV3 harder than the bulk.
[0042] The hardness measurements are post sintering and prior to any post sintering treatment,
such as tumbling.
[0043] In one embodiment, the hardness gradient is such that:
- the first part of the surface is between 2% softer and +6% harder than the second
part of the surface; and
- the first part of the surface is between +0.5 and +10% harder than the bulk; and
- the second part of the surface is between +0.3% and 6% harder than the bulk.
[0044] The first part of the surface is the surface where the binder puller has been applied
to form an oxide / carbonate doped surface. The second part of the surface is the
surface opposing where the binder puller has been applied (the side opposing the oxide
/ carbonate doped surface). Optionally, the second part of the surface could be a
surface where a binder pusher has been applied to form a carbide doped surface.
[0045] This is also shown in table 1 below:
Table 1: Hardness differences
|
Hardness difference HV3 |
Hardness difference (%) |
First part of the surface (oxide / carbonate doped surface) vs second part of the
surface (side opposing oxide / carbonate doped surface) |
First part of the surface (the oxide / carbonate doped surface) is between 30HV3 softer
and 80HV3 harder. |
First part of the surface (the oxide / carbonate doped surface) is between 2% softer
and 6% harder. |
First part of the surface (oxide / carbonate doped surface) vs bulk |
First part of the surface (the oxide / carbonate doped surface) is between 5HV3 and
120HV3 harder than the bulk. |
First part of the surface (the oxide / carbonate doped surface) is between 0.5% and
10% harder than the bulk. |
Second part of the surface (side opposing oxide / carbonate doped surface) vs bulk |
Second part of the surface (the side opposing the oxide / carbonate doped surface)
is between 20HV3 and 70HV3 harder than the bulk. |
Second part of the surface (the side opposing the oxide / carbonate doped surface)
is between 0.3% and 6% harder than the bulk. |
[0046] By the term "bulk" is herein meant the cemented carbide of the innermost part (centre)
of the rock drill insert and for this disclosure is the zone having the lowest hardness.
[0047] The hardness of the cemented carbide inserts is measured using Vickers hardness mapping.
The cemented carbide bodies, are sectioned along the longitudinal axis and polished
using standard procedures. Vickers indentations at a 3 kg load are then symmetrically
distributed over the polished section. The rhombuses in figures 3-13 and 16 show the
locations of the HV3 indentations. The hardness measurements are performed using a
programmable hardness tester, KB30S by KB Prüftechnik GmbH calibrated against HV3
test blocks issued by Euro Products Calibration Laboratory, UK. Hardness is measured
according to ISO EN6507.
HV3 measurements were done in the following way:
- Scanning the edge of the sample.
- Programming the hardness tester to make indentations at specified distances from the
edge of the sample.
- Indentation with 3 kg load at all programmed co-ordinates.
- The computer moves the stage to each co-ordinate with an indentation and runs auto
adjust light, auto focus and the automatically measures the size of each indentation.
- The user inspects all the photos of the indentations for focus and other matters that
disturb the result.
[0048] The HV3 measurements for the oxide / carbonate doped surface and side opposing the
oxide / carbonate doped surface were measured at a distance between 0.3 and 0.8 mm
below the surface, with 10-40 indentations being made and then the average HV3 measurement
calculated. The HV3 measurement for the bulk is measured in near the centre of the
polished section at the position having the lowest hardness, over an area of about
1.5-2 mm
2, taking the average from about 15-20 indentations.
[0049] In one embodiment, the maximum concentration (%binder-max) is less than 20% higher
than the minimum concentration (%binder-min) within the cemented carbide mining insert.
[0050] In one embodiment, the %binder-min (e.g. minimum Co concentration / %Co-min) is at
a depth, in percentage of the total height of the sintered cemented carbide mining
insert, of between 1-50% from the first part of the surface, preferably between 5-40%.
The %binder-min is typically at a depth of 0.5-10 mm, preferably 0.8-7 mm from the
first part of the surface.
[0051] In one embodiment, there are two peaks in binder concentration, one near the surface
and one in the bulk of the cemented carbide mining insert. There is a first maximum
binder concentration (%binder-max1) (e.g. %Co-maxl) at the first part of the surface
(e.g. at the oxide / carbonate doped surface) and a second maximum binder concentration
(%binder-max2) (e.g. %Co-max2) at a depth, in percentage of the total height of the
cemented carbide mining insert, of between 15-75% from the first part of the surface
(e.g. from the oxide / carbonate doped surface), preferably between 20-65%. In one
embodiment, %binder-max1 ≥ %binder-max2. In an alternative embodiment, %binder-max1
≤ %binder-max2. The %binder-max2 is typically 2-15 mm from the first part of the surface,
preferably between 4 -12 mm. The difference in the height of the %binder-min and %binder-max2
is typically between 1.5-12 mm, preferably between 2.5-10 mm.
[0052] In one embodiment, there is a first chromium concentration maximum (%Cr-max1) at
the first part of the surface (e.g. at the oxide/carbonate doped surface). In one
embodiment, there is additionally a second chromium concentration maximum (%Cr-max2)
at the surface second part of the surface (e.g. the surface opposing to oxide/carbonate
doped surface), wherein %Cr-max1>%Cr-max2. The chromium concentration minimum (%Cr-min)
is located between %Cr-max1 and %Cr-max2, in the bulk of the cemented carbide mining
insert. The %Cr-min is preferably at a depth, in percentage of total height of the
sintered cemented carbide mining insert, of 40-99%, more preferably at a depth of
50-98% from the first part of the surface. "At the surface" is defined as up to 0.3
mm from the surface.
[0053] The chemical concentrations within the cemented carbide mining insert are measured
using wavelength dispersive spectroscopy (WDS) along the centreline of a cross sectioned
cemented carbide mining insert.
[0054] Another aspect of the present disclosure relates to the use of the cemented carbide
mining insert as described hereinbefore or hereinafter for rock drilling or oil and
gas drilling.
[0055] The following examples are illustrative, non-limiting examples.
EXAMPLES
Example 1 - only binder puller applied
[0056] Table 2 shows a summary of the samples analysed:
Table 2: Summary of samples measured
Sample |
Powder blend |
Slurry applied to surface |
Tumbling treatment |
A |
94 wt% WC + 6 wt% Co |
None |
None |
B |
94 wt% WC + 6 wt% Co |
None |
Standard |
C |
94 wt% WC + 6 wt% Co |
None |
HET |
D |
94 wt% WC + 6 wt% Co |
Carbide doped slurry |
None |
E |
94 wt% WC + 6 wt% Co |
Carbide doped slurry |
Standard |
F |
94 wt% WC + 6 wt% Co |
Carbide doped slurry |
HET |
G (invention) |
94 wt% WC + 6 wt% Co |
Oxide doped slurry |
None |
H (invention) |
94 wt% WC + 6 wt% Co |
Oxide doped slurry |
Standard |
I (invention) |
94 wt% WC + 6 wt% Co |
Oxide doped slurry |
HET |
J (invention) |
89 wt% WC + 11 wt% Co |
Oxide doped slurry |
None |
K (invention) |
89 wt% WC + 11 wt% Co |
Oxide doped slurry |
HET |
[0057] For sample A to I in Table 2 the cemented carbide inserts were produced using a powder
blend having a composition of 94 wt% WC and 6 wt% Co. The WC powder grain size measured
as FSSS was before milling between 5 and 7 µm. The WC and Co powders were milled in
a ball mill in wet conditions, using ethanol, with an addition of 2 wt% polyethylene
glycol (PEG 8000) as organic binder (pressing agent) and cemented carbide milling
bodies. After milling, the slurry was spray-dried in N
2-atmosphere and then uniaxially pressed into mining inserts having a size of about
12 mm in outer diameter (OD) and about 17-20 mm in height (sample B = 18.7mm height;
sample C = 17.4mm height; sample D = 18.7mm height; sample E and F =17.4mm height;
samples G, H and I = 20.2mm height) with a weight of approximately 14-17g each with
a spherical dome ("cutting edge") on the top. The inserts were ground on the negative
part but leaving the dome and bottom part in an as-sintered condition.
[0058] Samples A, B and C had no slurry applied. Samples D, E and F are examples are comparative
examples where only a binder pusher, in the form of a "carbon doped slurry", was applied,
using a dipping technique, to the top, domed surface of the cemented carbide mining
inserts. The carbon doped slurry consisted of 25 wt% Cr
3C
2 and 5 wt% graphite dispersed in water and was applied to the cemented carbide insert
so that about 60% of the total insert length was exposed to the carbide doped slurry.
Samples F, G and H are examples of the invention where only a binder puller is applied,
the samples were treated by applying an "oxide doped slurry", comprising 30 wt% Cr
3O
2 and 70 wt% PEG300, to the domed surface of the cemented carbide insert in an amount
of between 0.25 -0.28 mg/mm
2, with about 60% of the total insert length exposed to the oxide slurry. All the samples
were sintered using Sinter-HIP in 55 bar Ar-pressure at 1410°C for 1 hour. For these
examples, the slurry was applied symmetrically, i.e. applied to the domed surface
extending an equal distance down the each of the sides of the insert.
[0059] Samples B, E and H were tumbled using "standard tumbling", using an ERBA-120 centrifugal
tumbler at 120 RPM for 30 minutes. Samples C, F and I were tumbled using "High energy
tumbling (HET)", using an ERBA-120 centrifugal tumbler 170 RPM or 40 minutes.
[0060] Samples J and K are examples of the invention where the cemented carbide inserts
have a higher binder content. The cemented carbide inserts were produced using a powder
blend having a composition of 89 wt% WC and 11 wt% Co. The WC powder grain size measured
as FSSS was before milling between 8 and 12 µm. The WC and Co powders were milled
in a ball mill in wet conditions, using ethanol, with an addition of 2 wt% polyethylene
glycol (PEG 8000) as organic binder (pressing agent) and cemented carbide milling
bodies. After milling, the slurry was spray-dried in N
2-atmosphere and then uniaxially pressed into mining inserts having a size of about
17 mm in outer diameter (OD) and about 22 mm in height, with a weight of approximately
31 g each with a conical tip ("cutting edge") on the top. The inserts were ground
on the cylindrical part but leaving the conical tip and the bottom part in an as-sintered
condition.
[0061] Samples J and K are examples of the invention where only a binder puller is applied,
the samples were treated by applying an "oxide doped slurry", using a dipping technique,
comprising 30 wt% Cr
3O
2 and 70 wt% PEG300, covering the conical tip and part of the cylindrical section in
an amount of between 0.25-0.35 mg/mm
2 so that approximately 75% of the total length of the insert was exposed to the oxide
doped slurry. The samples were sintered using Sinter-HIP in 55 bar AR-pressure at
1410°C for 1 hour. For these examples, the slurry was applied symmetrically, i.e.
applied to the domed surface extending an equal distance down the each of the sides
of the insert.
[0062] Samples K was tumbled using "High energy tumbling (HET)", in a Rösler model FKS 04.1
E-SA centrifugal tumbler at 250 RPM for 60 minutes with 50kg of media in the form
of carbide balls of 7mm in diameter.
[0063] Figures 3-13 show the HV3 iso-hardness maps for samples A - I respectively and Figures
15-18 shows the centre lines plots for samples A-K from Table 2. The hardness profiles
of the cemented carbide inserts are as described Table 1. The binder puller was applied
to the tip (30) of the cemented carbide mining insert, as shown in figure 14.
[0064] It can be seen that the hardness profiles of the present invention are very different
to the prior art and show that there is a softer core zone in the bulk and higher
hardness at both the top and the bottom of the cemented carbide mining insert.
Example 2 - binder puller and binder pusher applied
[0065] Cemented carbide inserts were formed using the same starting material as samples
J and K (89 wt% WC + 11 wt% Co) and method as described in table 2 / example 1. Mining
inserts were formed by uni-axial pressing having a length of 24 mm and a cylindrical
base of 19 mm diameter and a spherical (half dome) tip. Two PEG slurries were made
up, the first a "binder puller", which consisted of 30%Cr
2O
3+PEG and the second a "binder pusher", which consisted of 25%Cr
3C
2+5%C+PEG. The slurries were then applied to the surface of the inserts by dipping
the inserts into the slurry. The inserts were then sintered at 1410°C, 50 bar pressure
in an argon atmosphere. In this example, the two slurries were applied asymmetrically
to opposing sides i.e. the binder puller was applied to the side of the insert (10)
and the binder pusher was applied opposite (20) to this as shown in figure 2. The
HV5 iso-hardness map is shown in figure 19. It can be seen that a softer core is produced
using this method, this hardness profile has been shown to provide efficient drilling
behavior. The two slurries could have alternatively been applied symmetrically as
shown in figure 1. By controlling the concentration and positioning of the application
of the two slurries this facilitates the ability to be able to tailor the redistribution
of the binder phase to meet the needs of the application.
Example 3 - Insert compression test
[0066] The toughness of drill bit inserts of samples B, C, E, F, H and I described in table
2 / example 1 were characterized using an insert compression (IC) test. The IC test
method involves compressing a drill bit insert between two plane-parallel hard counter
surfaces, at a constant displacement rate, until the failure of the insert. A test
fixture based on the ISO 4506:2017 (E) standard "Hardmetals - Compression test" was
used, with cemented carbide anvils of hardness exceeding 2000 HV, while the test method
itself was adapted to toughness testing of rock drill inserts. The fixture was fitted
onto an Instron 5989 test frame.
[0067] The loading axis was identical with the axis of rotational symmetry of the inserts.
The counter surfaces of the fixture fulfilled the degree of parallelism required in
the ISO 4506:2017 (E) standard, i.e. a maximum deviation of 0.5 µm / mm. The tested
inserts were loaded at a constant rate of crosshead displacement equal to 0.6 mm /
min until failure, while recording the load-displacement curve. The compliance of
the test rig and test fixture was subtracted from the measured load-displacement curve
before test evaluation. Three inserts were tested per sample type. The counter surfaces
were inspected for damage before each test. Insert failure was defined to take place
when the measured load suddenly dropped by at least 1000 N. Subsequent inspection
of tested inserts confirmed that this in all cases this coincided with the occurrence
of a macroscopically visible crack. The material toughness was characterized by means
of the total absorbed deformation energy until fracture. The results of the insert
compression test are shown in Table 3:
Table 3: Summary of Insert compression test results
Sample |
Deformation energy until fracture (J) |
B |
7.37 |
C |
8.87 |
E |
7.27 |
F |
9.96 |
H (invention) |
9.75 |
I (invention) |
12.50 |
[0068] The toughness of the samples treated according to the method the present invention
is higher than samples known in the prior art according to the IC test results when
comparing samples that were tumbled in the same way.
Example 4- Pendulum Hammer
[0069] For the Pendulum Hammer test cemented carbide mining inserts with a dome shaped tip
of 5.0 mm radius and a diameter of 10.0 mm were produced and treated in the same way
samples B, C, E, F, H and I as described in example 1. A schematic drawing of the
pendulum hammer test set-up is shown in figure 20. The inserts were firmly mounted
into a holder (30) with only the dome section protruding. On the pendulum (40) a hard-counter
surface is mounted (50) on the pendulum hammer head. The counter surface used was
a polished plate (h = 5.00 mm, l = 19.40 mm, w = 19.40 mm) of a hard, fine grained
hard metal grade having a Vickers hardness of approx. 1900 HV30. When the pendulum
is released, the counter surface hits the sample tip. If the sample fails, the impact
energy (E) absorbed by the sample measured in Joules (J) is not recorded. For a given
initial pendulum angle, the impact energy is calculated using equation 3 where m is
the total mass of the pendulum hammer 4.22 kg, g is the gravitational constant 9.81
m/s2, L is the pendulum hammer length 0.231 m and α is the angle in radians.
[0070] To determine the energy needed to fracture the sample, it is first impacted by the
pendulum released from a suitable low angle. The angle is then increased step-wise
with a 5 degree step until the sample fails. Following this, inserts from the same
sample are impacted at a 3 degree lower angle than the impact angle that caused the
failure and the test is repeated with smaller incremental increases in the impact
angle. The angle where the insert does not break is recorded and the corresponding
impact energy calculated. In these tests, the counter surface was exchanged every
5-10 impacts. The results are shown in table 4 below:
Table 4: Summary of Pendulum Hammer test results
Sample |
Impact energy (J) |
B |
6.9 |
C |
10.3 |
E |
6.0 |
F |
8.3 |
H (invention) |
7.7 |
I (invention) |
15.0 |
[0071] The results show that there is a significant increase in the impact resistance for
the sample produced using the method of the current invention when comparing samples
tumbled in the equivalent way.
Example 5 - Chemical analysis
[0072] The chemical gradient of the sample was investigated by means of wavelength dispersive
spectroscopy (WDS) analysis using a Jeol JXA-8530F microprobe. Line scans along the
centre line were done on cross sections of the sintered materials, prior to tumbling
for samples D (comparison) and G (invention) as described in table 2 / example 1.
Samples were prepared by precision cutter, followed by mechanical grinding and polishing.
The final step of the sample preparation was carried out by polishing with 1 µm diamond
paste on a soft cloth. An acceleration voltage of 15kV was used to perform line scans
with a step size of 100µm and a probe diameter of 100µm. Three line scans per sample
were carried out and the average is reported. The cobalt concentration profiles are
compared in figure 21, the chromium concentration profiles are compared in figure
22 and the Cr/Co concentration profiles are compared in figure 23.
[0073] For comparison with a cemented carbide mining insert having a higher binder concentration,
line scans along the centre line were done on cross sections of sample K post tumbling.
Tumbling is assumed not to affect the chemical composition nor the WDS analysis. The
lines scans for the Co concentration and the Cr concentration are shown respectively
in figures 24 and 25.
[0074] It can be seen that for the samples produced according to the method of this invention
that the highest Co concentration can be found in the tip and the bulk of the cemented
carbide insert; and the lowest Cr concentration and lowest Cr/Co concentration is
found in the bulk of the cemented carbide insert.
1. A method of redistributing the binder phase of a cemented carbide mining insert comprising
a WC hard-phase component, optionally one or more further hard-phase components and
a binder comprising the steps of:
a) providing a green cemented carbide mining insert;
b) applying at least one binder puller selected from a metal oxide or a metal carbonate
to the surface of the cemented carbide mining insert; and
c) sintering the green carbide mining insert;
characterized in that the metal oxide or metal carbonate is only applied to at least one local area on
the surface of the green cemented carbide mining insert.
2. The method according to claim 1 wherein the binder puller is Cr2O3.
3. The method according to claim 1 or claim 2 further comprising the step between steps
b) and c) of:
applying at least one binder pusher, selected from a metal carbide, a carbon powder
or a mixture thereof, to at least one different local area on the surface of the cemented
carbide mining insert.
4. The method according to any of the previous claims, wherein the binder puller and
the binder pusher are applied to substantially opposing local areas of the surface
of the green cemented carbide mining insert.
5. The method according to any of the previous claims, wherein the binder puller and
the binder pusher are applied symmetrically.
6. The method according to any of the previous claims, wherein the binder puller and
binder pusher are applied asymmetrically.
7. The method according to any of the previous claims, wherein post sintering the cemented
carbide mining insert is treated with a tumbling process.
8. The method according to claim 7, wherein the tumbling process is a "High Energy Tumbling"
process, wherein post tumbling a homogenous cemented carbide mining insert has been
deformation hardened such that ΔHV3% ≥ 9.72 - 0.00543*HV3bulk.
9. A cemented carbide mining insert comprising one or more hard-phase components and
a binder
characterized in that there is a hardness gradient from a first part of the surface to a second part of
the surface of the cemented carbide mining insert, wherein the first part of the surface
is substantially opposing the second part of the surface, such that post sintering:
- the first part of the surface is between 30HV3 softer and 80HV3 harder than the
second part of the surface; and
the first part of the surface is between 5 and 120 HV3 harder than the bulk; and
- the second part of the surface is between 20HV3 and 70HV3 harder than the bulk
10. A cemented carbide mining insert according to claim 9, wherein
the maximum binder concentration (%binder-max) is less than 20% higher than the minimum
concentration (%binder-min) within the cemented carbide mining insert.
11. A cemented carbide mining insert according to claim 9 or claim 10, wherein the %binder-min
is at a depth, in percentage of the total height of the sintered cemented carbide
mining insert, of between 1-50% from the first part of the surface.
12. A cemented carbide mining insert according to any of claims 9-11, wherein:
- there is a first binder concentration maximum (%binder-max1) at the first part of
the surface; and
- there is a second binder concentration maximum (%binder-max2) at a depth, in percentage
of the total height of the sintered cemented carbide mining insert, of between 15-75%
from the first part of the surface.
13. A cemented carbide mining insert according to any of claims 9-12, wherein there is
a first chromium concentration maximum (%Cr-max1) at the first part of the surface.
14. A cemented carbide mining insert according to claim 13, wherein there is additionally
a second chromium concentration maximum (%Cr-max2) at the second part of the surface;
- %Cr-max1>%Cr-max2; and
- there is a chromium concentration minimum (%Cr-min) located between %Cr-max1 and
%Cr-max2.
15. A cemented carbide mining insert according to claim 14, wherein the %Cr-min is at
depth, in percentage of the total height of the sintered cemented carbide mining insert,
of between 40-99%, from first part of the surface.