Note: Descriptions are shown in the official language in which they were submitted.
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CEMENTED CARBIDE INSERT FOR MINING OR CUTTING APPLICATIONS COMPRISING GAMMA
PHASE CARBIDE
TECHNICAL FIELD
The present invention relates to a cemented carbide insert for mining or
cutting applications
containing gamma phase carbide and a method of making said mining insert.
BACKGROUND
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. Cemented
carbide comprises
a hard metal phase and a binder phase. Typically, the cemented carbide used
for mining inserts
using tungsten carbide hard metal phase, with only very minor quantities of
other carbides that are
present as impurities rather than purposely added.
The use of gamma phase hard metals which includes cubic carbides and nitrides
and
carbonitrides of titanium, tantalum and niobium carbide that together with
hexagonal tungsten
carbide form a mixed cubic carbide (Mel, Me2, Me3)(C) or mixed cubic
carbonitride (Mel, Me2,
Me3)(C,N), so called gamma phases, are commonly used in cemented carbides used
in the metal
cutting industry as they provide the benefit of improved wear resistance and
improved resistance
towards plastic deformation. However, gamma phase hard metals are not
currently used in
cemented carbide for mining inserts as it embrittles the carbide, which when
subjected to mining
operations, such as a percussive drilling action, will result in the inserts
prematurely cracking,
therefore reducing the lifetime of the inserts.
DEFINITIONS
By "cemented carbide" is herein meant a material that comprises at least 50
wt% WC,
possibly other hard constituents common in the art of making cemented carbides
and a metallic
binder phase preferably selected from one or more of Fe, Co and Ni.
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.
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.
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The term "cubic carbides" refers to the cubic carbides such as TaC, NbC, TiC
that together
with hexagonal WC will form a cubic "gamma phase" during sintering.
The term "cubic nitrides" refers to cubic nitride such as TiN that together
with hexagonal WC
will form a cubic "gamma phase" during sintering.
The term "cubic carbonitrides" refers to the cubic carbonitride such as
Ti(C,N) that together
with hexagonal WC will form a cubic "gamma phase" during sintering.
The term "gamma phase" refers to the mixed cubic carbides and carbonitrides
formed and
precipitated during sintering when cubic carbide and/or nitride
formers/precursors are added prior
to the green forming step in higher amounts than can be dissolved in the
binder in the sintered
cemented carbide body. Typical cubic gamma phase formers/precursors are for
example Ta, Nb and
Ti that together with W from the hexagonal WC form the cubic gamma phase for
example, but not
limited to, (Ta,Nb,W)(C), (Ta, Nb, Ti, W)(C,N). It is assumed that
substantially all added cubic
carbides/nitrides/carbonitrides form "gamma phase" and the amount of these
cubic gamma phase
precursors in the sintered body is either calculated from the sum of the added
cubic
carbide/nitrides/carbonitrides or can be calculated backwards by analysing the
element
concentration of Mel, Me2 including nitrogen in the sintered body and assume
that all Mel was
added as Me1C, where Mel is a metal that form cubic carbides as Ta or Nb. If
nitrogen is present
some of the Me2 was added as Me2N or Me2(C,N) and Me2C, where Me2 is a metal
that forms both
cubic carbides, nitrides and mixtures thereof as Ti. The elemental analyses
are preferably performed
using an XRF-instrument equipped with a wavelength dispersive spectrometer on
an oxidised and
dissolved sintered material that for example is included into a light element
(as boron) glass. The
analysis and evaluation are performed using quantitative XRF-methods that are
carefully calibrated
within the range of the claims.
SUMMARY OF INVENTION
A cemented carbide mining insert having improved wear resistance without
increased
brittleness has now been developed. Different aspects of the invention include
a cemented carbide
mining insert, a rock drill bit body comprising one or more mounted cemented
carbide inserts, and a
method of producing a cemented carbide insert, which are characterized by what
is stated in the
independent claims. Various embodiments of the invention are disclosed in the
dependent claims.
According to a first aspect of the present invention there is a sintered
cemented carbide
insert for mining or cutting applications comprising: a mean WC grain size of
between 0.8 ¨ 18 iim; a
binder phase in a weight between 4 - 18 wt%; gamma phase with the cubic gamma
phase precursors
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in a weight of between 0.8 - 10 wt%; any unavoidable impurities and a balance
of WC; and wherein
the difference between the hardness at 0.3 mm at any point from the surface of
the insert and the
hardness of the bulk is at least 25 HV3, wherein hardness is measured
according to ISO EN6507
3:2005.
Advantageously, a cemented carbide mining insert having improved wear
resistance without
increased brittleness is provided. Therefore, the lifetime of the insert is
increased. Further, it makes
it easier to be able to use recycled carbide, that typically has higher gamma
phase content that
would be acceptable for cemented carbide grades that are commonly used for
used mining or
cutting applications. A cemented carbide insert should be considered to
include any insert used for
interaction with rock, for example inserts for percussive drilling, top hammer
drilling, down-the-hole
(DTH) drilling, protection inserts or cutting tools.
According to second aspect of the present invention there is a method of
producing a
cemented carbide insert, comprising the steps of:
a) providing a green cemented carbide insert comprising between 0.8 - 10 wt%
cubic
carbides and or carbonitrides and or nitrides, between 4- 18 wt% binder, any
unavoidable
impurities and a balance of WC hard phase;
b) sintering the green carbide mining insert to form a sintered cemented
carbide insert;
c) subjecting the sintered cemented carbide insert to a high energy post-
treatment.
Advantageously, this method produces cemented carbide inserts having improved
wear
resistance without increased brittleness and therefore the inserts produced by
this method have an
increased lifetime.
According to a third aspect, there is provided a rock drill bit body
comprising one or more
mounted cemented carbide inserts.
BRIEF DECRSIPTION OF DRAWINGS
Figure 1: Schematic drawing showing the positions on the insert where the
hardness and toughness
measurements were taken.
Figure 2. Schematic drawing of a top hammer bit with ballistic inserts with
the diameter measuring
points indicated.
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DETAILED DESCRIPTION
The present invention relates to a sintered cemented carbide insert for mining
or cutting
applications comprising: a mean WC grain size of between 0.8 ¨ 18 pLm; a
binder phase in a weight
between 4 - 18 wt%; gamma phase with the cubic gamma phase precursors in a
weight of between
0.8 - 10 wt%; any unavoidable impurities and a balance of WC; and wherein the
difference between
the hardness at 0.3 mm from any point of the surface of the insert and the
hardness of the bulk is at
least 25 HV3, when the hardness is measured according to ISO EN6507.
Preferably the sintered WC grain size is between 0.8 - 16 p.m, more preferably
between 0.8 -
8 urn or 0.8 -5 p.m or 0.9 - 8 p.m or 1.0- 5 p.m or 1.0 ¨ 4.0 pm.
The mean WC grain size was evaluated using the Jeffries method described
below, from at
least two different micrographs for each material. An average value was then
calculated from the
mean grain size values obtained from the individual micrographs (for each
material respectively).
The procedure for the mean grain size evaluation using a modified Jeffries
method was the
following:
A rectangular frame of suitable size was selected within the SEM micrograph so
as to contain
a minimum of 300 WC grains. The grains inside the frame and those intersected
by the frame are
manually counted, and the mean grain size is obtained from equations (1-3):
M = Lscale mmX 1
¨3
(1)
Lscale microX10¨ 6
( rwt%Co
l 1)
VO/VOWC = 100 X ¨1.308823529 x Imo
(wt%c +1.308823529)
100
(2)
1500 Li xL2 xvo/0/0 WC
d= ¨ x (3)
M (ni -F71 )X100
2
Where:
d = mean WC grain size (pm)
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L1, L2 = length of sides of the frame (mm)
M = magnificationLscale mm = measured length of scale bar on micrograph in mm
Lscale micro = actual length of scale bar with respect to magnification (pm)
ni = no. grains fully within the frame
5 nz = no. grains intersected by frame boundary
wt%Co = known cobalt content in weight %.
Equation (2) is used to estimate the WC fraction based on the known Co content
in the
material. Equation (3) then yields the mean WC grain size from the ratio of
the total WC area in the
frame to the number of grains contained in it. Equation (3) also contains a
correction factor
compensating for the fact that in a random 2D section, not all grains will be
sectioned through their
maximum diameter.
Preferably, the binder phase is between 4- 18 wt% or 5 - 15 wt% or 5 - 12 wt%
or 6 - 12 wt%
or 5 -8 wt% and 10 - 15 wt%.
For percussive applications as Top hammer (TH) and Down the Hole (DTH) the
grain sizes are
preferable between 0.8 - 5 microns and the binder phase concentration is
preferable between 4 ¨ 8
wt% and the room temperature hardness is preferable between 1250¨ 1650 HV20.
For Rotary applications the grain size is preferable between 2- 8 microns and
the binder
phase content is preferable between 8¨ 15 wt% and the room temperature
hardness is between
1000 ¨ 1400 HV20.
For mechanical cutting applications the grain sizes are preferable between 6 ¨
18 microns
and the binder phase content are between 6 ¨ 18 wt% and the room temperature
hardness is
preferable between 800¨ 1200 HV20.
Preferably, the weight percent of gamma phase is less than 10 wt%, more
preferably less
than 8 wt% even more preferable less than 6 wt% or less than 4 wt% or less
than 2 wt%.
Preferably, the weight percent of gamma phase is > 0.8 wt%, more preferably >
0.9 wt%,
more preferable > 1.0 wt%, even more preferable > 1.1 wt%, even more
preferably >1.2 wt%.
The gamma phase forming carbides or nitrides or carbonitrides added could be
any of Ta,
Nb, Ti, Zr, Hf.
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Preferably, the volume of gamma phase is evenly distributed throughout the
insert.
Preferably, the gamma phase grains are smaller than 10 microns, more
preferable smaller
than 5 microns, preferable smaller than 4 microns most preferable smaller than
3 microns.
The hardness of the cemented carbide inserts is measured using Vickers
hardness
measurement. The cemented carbide bodies are sectioned along the longitudinal
axis and polished
using standard procedures. The sectioning is done with a diamond disc cutter
under flowing water.
In one embodiment the difference between the hardness at 0.3 mm depth at any
point of
the surface of the dome of the rock drill insert and the minimum hardness of
the bulk of the rock
drill insert is at least 25 HV3 or at least 30 HV3 or at least 35 HV3, or at
least 40 HV3. The average
hardness at a certain depth is defined as the average of at least 10 measured,
more preferable 20
hardness values at the certain depth evenly distributed around the insert. The
large difference in
hardness between the surface of the rock drill insert and its interior is
present over the whole
surface and will therefore also reduce the risk of other types of failures
during handling.
Preferably, the cemented carbide insert has a bulk hardness of not higher than
1700 HV3 or
not higher than 1650 HV3, or not higher than 1600 HV3.
In one embodiment the top of the insert has a higher surface hardness than the
cylindrical
part and the bottom, but the bulk hardness is the same in the interior of the
insert.
Preferably, the binder phase comprises at least 80wt% of one or more of
cobalt, nickel, iron
or a combination thereof.
Preferably the binder phase is Co and / or Ni, most preferably Co, even more
preferably
between 3 to 20 wt% Co. Optionally, the binder is a nickel chromium or nickel
aluminium alloy.
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.
The binder content may be constant throughout the insert or have a gradient
from the surface
to the bulk of the insert.
Preferably, the cubic precursors for gamma phase is tantalum carbide or
niobium carbide or a
mixture thereof. This is beneficial for the plastic deformation resistance at
elevated temperature.
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Preferable the amount of TaC+NbC= 0.8 - 10 wt% or 1 - 8 wt% or 1 - 5 wt% or
1.2 ¨ 5 wt% or 1.2
to 3 wt% or 1.5 - 6 wt%.
Preferably, the ratio of Ta / Nb in weight is 0.1 - 100, more preferable 0.5 -
50, even more
preferable 1 - 10, most preferable 2 ¨ 6.
Optionally, the cemented carbide also comprises Cr in such an amount that the
mass ratio Cr/Co
in the bulk is 0.04 - 0.19. Preferably, the mass ratio Cr/Co in the cemented
carbide is 0.06 - 0.16,
more preferably the mass ratio Cr/Co in the cemented carbide is 0.07 - 0.15,
most preferable the
mass ratio Cr/Co in the cemented carbide is 0.075 - 0.12. Advantageously, the
presence of the
chromium improves the plastic deformation of the cemented carbide, this
enables higher
compressive stresses to be introduced into the carbide when it is treated with
a surface high energy
post-treatment, such as tumbling or intensive shaking. This increase in
compressive stress provides
an apparent hardness increase which improves the wear resistance of the
cemented carbide,
without reducing the toughness.
The mass ratio of the Cr/binder is calculated by dividing the weight
percentage (wt%) of the Cr
added to powder blend by the wt% of the binder in the powder blend, wherein
the weight
percentages are based on the weight of that component compared to the total
weight of the
powder blend. To a great extent the Cr is dissolved into the binder phase,
however there could be
some amount, e.g. up to 3 mass%, of undissolved chromium carbide in the
cemented carbide body.
It may however be preferable to only add Cr up to the mass ratio of Cr/binder
so that all the Cr
dissolved into the binder so that the sintered cemented carbide body is free
of undissolved
chromium carbides.
The Cr is normally added to the powder blend in the form of Cr3C2 as this
provides the highest
proportion of Cr per gram of powder, although it should be understood that the
Cr could be added
to the powder blend using an alternative chromium carbide such as Cr26C2 or
Cr7C3 or a chromium
nitride or even a oxide. The addition of the Cr also has the effect of
improving the corrosion
resistance of the cemented carbide body. The presence of the Cr also makes the
binder prone to
transform from fcc to hcp during drilling, this is beneficial for absorbing
some of the energy
generated in the drilling operation. The transformation will thereby harden
the binder phase and
reduce the wear of the button during use thereof. The presence of the Cr will
increase the wear
resistance of the cemented carbide and increase its ability for deformation
hardening. The
combination of the Cr in the cemented carbide powder and the application of
the powder
comprising a grain refiner compound and optionally a carbon-based grain growth
promoter, to at
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least one portion of the surface of the compact produces a cemented carbide
body having a
chemical and hardness gradient which produce a cemented carbide mining insert
with high wear
resistance.
In one embodiment of the present invention, the cemented carbide comprises
M7C3 carbides
and / or M23C6 carbide, and possibly also M3C2 carbides, where M is Cr and
possibly one or more of
W, Co and any other elements added to the cemented carbide. By that is herein
meant that the
M7C3 and / or M23C6 carbide carbides should be clearly visible in a SEM
(scanning electron
microscope) image using backscattering at a magnification enough to detect
particles of a size of 100
nm. In one embodiment of the present invention, the cemented carbide comprises
M7C3 carbides
and / or M23C6 carbides in an amount given by the ratio vol% (M7C3 carbides
and / or M23C6 carbide) /
vol% Co. Suitably the ratio vol% (M7C3 carbides and / or M23C6 carbide) / vol%
Co is between 0.01 to
0.5 preferably between 0.03 to 0.25. The vol% of M7C3 carbides and / or M23C6
carbide and the Co
binder can be measured by EBSD or image analysis using a suitable software.
In one embodiment the cemented carbide is free from eta phase and graphite. If
the binder
phase consists of cobalt, the cemented carbide will be free from eta phase and
graphite when the
Com/Co ratio is 0.75 Com/Co0.98. The metals used as binder phase in
cemented carbides, like
Co, Ni, and Fe are ferromagnetic. The saturation magnetization is the maximum
possible
magnetization of ferromagnetic material, characterized by parallel orientation
of all magnetic
moments inside the material. A Foerster KOERZIMAT 1.096 is used to determine
the magnetic
saturation (Corn) dipole moment jS and the derived weight specific saturation
magnetization GS
(47-ro-) of the inserts. The Co content is then measured with XRF (X-ray
fluorescence) using a Malvern
Panalytical Axios Max Advanced instrument. The Com/%Co range that is between
eta phase and
graphite formation is affected by changing the binder composition, such as by
adding Cr, Fe, Ni etc.
The solubility of W in the binder phase is directly related to the carbon
content. The amount of
W in the binder increases with decreasing carbon content until the limit for
eta phase formation is
reached. If the carbon content would decrease even lower, the solubility of W
in the binder will not
increase further. In some cemented carbide grades where it is beneficial to
obtain a high amount of
W dissolved in the binder, the carbon content has been kept low but above the
limit for eta phase
formation.
In one embodiment, the fracture toughness difference (Delta K1C) between 0.5
mm below the
surface and the bulk is at least 1.5, more preferably at least 1.8, even
preferable at least 2.0, most
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preferable at least 2.2 MPa*mas. The fracture toughness K1C is measured using
5- 10 Vickers
indentations, 30 kg load and calculated using Shetty's formula.
Figure 1 shows the positions where the indentations were placed for delta K1C
and delta HV3
measurements. On the left side of the sectioned and polished sample HV30
indentations were
placed 0.5 mm from the surface 10 (unfilled diamonds) and in the bulk 20
(black diamonds). On the
right side of the sample HV3 was measured 0.3 mm from the surface 30 (black
filled diamonds), 1
mm from the surface 40 (grey diamonds) and in the bulk 50 (light grey
diamonds).
In one embodiment, there is a rock drill bit body comprising one or more
mounted cemented
carbide inserts as described hereinabove or hereinbelow.
According to one embodiment, the cemented carbide inserts are mounted in a
rock drill bit body
of a top-hammer (TH) device or a down-the-hole (DTH) drilling device or a
rotary drilling device or a
cutting disc device. The rotary drilling device may be an oil and gas rotary
cutter device. The
invention also relates to a rock drill or cutting device, in particular a top-
hammer device, or a down-
the-hole drilling device, or a rotary drilling device, or a cutting disc
device as well as the use of a
cemented carbide insert according to the invention in such a device.
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.
Another aspect of the present invention is a method of producing a cemented
carbide insert
according to any of claims 1-7, comprising the steps of:
a) providing a green cemented carbide insert comprising between 0.8-10 wt%
cubic carbides
and or carbonitrides and or nitrides, between 4-18 wt% binder, any unavoidable
impurities
and a balance of WC hard phase;
b) sintering the green carbide mining insert to form a sintered cemented
carbide insert;
c) subjecting the sintered cemented carbide insert to a high energy post-
treatment.
High energy post-treatment (HET) is considered to be a process wherein a post -
treatment a
homogenous cemented carbide mining insert has been deformation hardened such
that FIV3%
9.72 ¨ 0.00543*HV3buik, wherein the AHV3% is the percentage difference between
the HV3
measurement at 0.3 mm from the surface compared the HV3 measurement in the
bulk. HET could
also be understood to mean a post- treatment process that induces a hardness
difference between
0.3 mm from the surface and the bulk of at least 20 HV3. HET could also be
understood to mean that
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there is both a hardness and toughness increase induced from the surface to
the bulk without
changing the chemical composition or the WC grain size near the surface (0.3
mm below) or in the
bulk.
To introduce higher levels of compressive stresses into the cemented carbide
mining insert,
5 a high energy shaking or tumbling process may be used. There are many
different possible process
set ups that could be used to introduce HET, including the type of equipment,
the volume of media
added (if any), the treatment time and the process set up, e.g. RPM for a
centrifugal tumbler or
shaking equipment 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
10 cemented carbide mining insert consisting of WC-Co, having a mass of
about 20g". In the present
disclosure, HET is defined as a post-treatment process that would introduce a
hardness change,
measured using HV3, after post-treatment (AFIV3%) of at least:
AHV3% = 9.72¨ 0.00543*HV3bulk (equation 1)
Wherein:
AHV3% = 100*(HV30.3mm ¨ HV3bulk)/HV3bulk (equation 2)
HV3buik is an average of at least 10 indentation points measured in the
innermost (centre) of
the cemented carbide mining insert and HV30.3m,, is an average of at least 10
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 HET-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.
HET may typically be performed using centrifugal tumbling in an ERBA 120,
having a disc size
of about 600 mm, run 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 300 RPM if the
media used is smaller in size than the inserts being tumbled; using a Rosier
tumbler, having a disc
size of about 350 mm, at about 280 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 320 RPM if the
media used is smaller in size than the inserts being tumbled. Typically, the
parts are tumbled for at
least 40-80 minutes. Using a commercially available paint shaker of trademark
CorobTM Evoshake500
with a maximum load of 40 kg and a maximum shaking frequency of 65 Hz
corresponding to 600
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rpm. One insert up to the maximum load of the machine of inserts are placed in
a plastic sealed
containers being cylindrical or square in shape optional together with almost
spherical cemented
carbide media of a hardness around 1200-1600 Vickers of sizes ranges from 3 ¨
20 mm in diameter
with a small amount of cooling liquid (water with an antioxidizing agent)
added, such that not all of
the inserts are covered in cooling liquid. The filling degree in the plastic
containers is preferable
between 20 ¨ 80 % of the volume, most preferable between 30-50 % of the
container volume. The
container is shaken for 5 -30 min using the 100% of the shaking capacity of
the machine (600 rpm),
preferable between 5-15 min which corresponds to or above the compressive
stress levels that can
be obtained in the ERBA 120 using the parameters above. Softer ramping steps
can be applied by
lower the rpm; this is beneficial if the inserts is prone to breaking. During
the shaking process the
inserts and the cooling liquid are heated up to about 70-90 degrees C.
In one embodiment, the high energy post treatment is conducted at an elevated
temperature of
or above 100 C, preferably at a temperature of or above 200 C, more preferably
at a temperature of
between 200 C and 450 C. The advantage the elevated process temperature is
that an increased
toughness of the carbide and hence the collisions do not result in defects
such as micro cracks, large
cracks or edge chipping. The higher level of compressive stress in combination
with decreased
collision defects will improve the fatigue resistance and fracture toughness
of the mining insert and
consequently increase the lifetime of the insert. Further advantages of this
method are that insert
geometries, such as those with a sharp bottom radius, which were previously
prone to excessive
damage to the corners and therefore low yields, can now be tumbled without
causing edge damage.
This opens the possibility to develop mining insert products with different
geometries, which were
previously not suitable for HET. The method also makes it possible to use
cemented carbide
compositions that would have previously been too brittle for mining
applications. The ability to
introduce higher levels of compressive stress means that the toughness of the
mining inserts is
increased to an acceptable level and thus mining inserts having a higher
hardness can be used which
is beneficial for increasing the wear resistance of the mining inserts.
In one embodiment of the present invention the mining insert is subjected to a
surface
hardening treatment at a temperature of between 150-250 C, preferably at a
temperature of
between 175-225 C.
In one embodiment of the present invention the mining insert is subjected to a
surface
hardening treatment at a temperature of between 300-600 C, preferably at a
temperature of
between 350-550 C, more preferably of between 450-550 C.
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The temperature is measured on the mining insert using any suitable method for
measuring
temperature. Preferably, an infrared temperature measurement device is used.
The effect of the surface hardening treatment at elevated temperatures is
enhanced if the
process is done in dry conditions. By "dry" conditions it is meant that no
liquid is added to the
process. Without being bound by this theory, it is thought that, if liquid is
introduced to the process,
it will keep the parts at room temperature. Further, the inclusion of the
liquid will reduce the degree
of the impact between the parts being HET-treated. Liquid prevents the
internal friction and
collision heat to increase the temperature in the collision points. If no
liquid is used, then the
temperature at the collision points gets high resulting in a higher toughness
of the material
subjected to the collision points.
Alternatively, the tumbler could be pressurized to a pressure that prevents
water from boiling so
that it would be possible to conduct the high temperature HET-treated in wet
conditions.
The HET process could be conducted in the presence or absence of media
depending on the
geometry and material composition of the mining inserts being tumbled. If it
is decided to add
media, the type and ratio of media to inserts is selected to suit the geometry
and material
composition of the mining inserts being HET-processed.
Optionally, all or part of the heat is generated by friction between the
inserts and any media
added in the HET process.
In one embodiment the inserts can be heated in a separate step prior to the
surface hardening
process step. Several methods can be used to create the elevated temperature
of the mining insert,
such as induction heating, resistance heating, hot air heating, flame heating,
pre-heating on a hot
surface, in an oven or furnace or using laser heating.
In one embodiment, the mining inserts are kept heated during the surface
hardening process.
For example, using an induction coil.
In one embodiment, all or part of the heat is generated by the friction
between the inserts and
any media added in the HET- process. Advantageously, this removes debris and
oxides, for example
iron oxide, that are deposited on the insert surfaces from the inside of the
process container. The
second surface hardening process performed at room temperature could be
performed in wet
conditions, which will aid in removing dirt and dust from the mining inserts
being treated which
reduces health hazards.
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In one embodiment, after the mining inserts have been subjected to the surface
hardening
process at an elevated temperature, the mining inserts are subjected to a
second surface hardening
process at room temperature.
In one embodiment, second surface hardening process is high energy tumbling.
In one embodiment, the high energy post-treatment is conducted by a bi-
directional shaking
process.
In one embodiment the main movement of the bi-directional shaking process is
in the vertical
direction and the minor movement is in the horizontal direction.
In one embodiment the bi-directional shaking process is conducted at 400-700
rpm for between
5-30 minutes. Preferably at between 500-600 rpm. Preferably for between 5-15
minutes.
EXAMPLES
Example 1 ¨ Samples
Table 1 shows the summary of the samples tested, including their compositions
and surface
hardening treatment. WC content is the balance in the example below.
Sample Co Cr TIC TIN TaC NbC Sinter
Bulk Post sintering
Wt Wt % Wt % Wt % Wt % Wt % ed WC hardnes treatment
grain
size HV20
(Pin)
A 6.0 - 1.91 1470 None
(comparative)
6.0 - 1.91 1470 5
min HET
(comparative)
6.0 - 1.91 1470 10
min HET
(comparative)
7.6 1.20 0.32 1.08 1490 none
(comparative)
E (invention) 7.6 1.20 0.32 1.08 1490
5 min HET
F (invention) 7.6 1.20 0.32 1.08 1490
10 min HET
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7.6 1.20 0.32 1.08 1490
HOT HET 20
(invention) min
7.2 - 1.90 0.40 2.90 0.49
1.53 1530 none
(comparative)
I (invention) 7.2 - 1.90 0.40 2.90 0.49 1.53
1530 5 min HET
J (invention) 7.2 - 1.90 0.40 2.90 0.49 1.53
1530 10 min HET
7.0 0.7 - 1.36 1480 none
(comparative)
7.0 0.7 - 1.36 1480 5
min HET
(comparative)
7.0 0.7 - 1.36 1480 10
min HET
(comparative)
7.0 0.7 - 1.10 0.30 1.41 1541
none
(comparative) HV3
0 (invention) 7.0 0.7 - 1.10 0.30 1.41 1541
5 min HET
HV3
6.3 0.63 - 1.00 0.20 - 1556 none
(comparative) HV3
Q (invention) 6.3 0.63 - 1.00 0.20 - 1556
5 min HET
HV3
9.0 0.9 - 0.5 1740 10
min HET
(comparative)
7 1.05 - 1.40 1535 5
min HET
(comparative)
Table 1: Summary of samples
All cemented carbide inserts were produced using a WC powder grain size
measured as FSSS
was before milling between 2 and 18 p.m. 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
3400) as organic
binder (pressing agent) and cemented carbide milling bodies. After milling,
the mixture was spray-
dried in N2-atmosphere and then uniaxially pressed into GT7S100A mining
inserts having a size of
about 10 mm in outer diameter (OD) and about 16-20 mm in height with a weight
of approximately
17g each with a spherical dome ("cutting edge") on the top. The samples were
then sintered using
Sinter-HIP in 55 bar Ar-pressure at 1410 C for 1 hour and then ground on the
cylindrical part.
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The samples that were HET were treated using a commercially available paint
shaker of
trademark CorobT" Evoshake500 with a maximum load of 40 kg and a maximum
shaking frequency
of 65 Hz (600 rpm). 20 inserts were placed in a plastic bucket height= 12 cm
OD= 10 cm together
with 3 kg 7 mm almost spherical cemented carbide media of a hardness around
1600 Vickers and 1
5 dl of water with an antioxidizing agent was added. The filling degree was
about 40%. The bucket was
shaken for 5 min using the 100% of the shaking capacity of the machine. Three
softer ramping steps
were also applied 30 s at 25%, 30 s at 50% and 30 s at 75% of the maximum
shaking capacity. After 5
min at max frequency 10 inserts were removed ("5 min HET") and then the same
program was
restarted for an additional 5 min at max frequency ("10 min HET").
10 Some inserts were treated at 300 C in a so called "HOT HET"
treatment using the paint
shaker of trademark CorobTM Simple Shake 90 with a maximum load of 40 kg and a
maximum shaking
frequency of 65 Hz (600 rpm). The hot shaking method was conducted at a
frequency of 5 Hz. About
800 grams or 50 pieces of inserts and 3.75 kg carbide media (7mm balls) where
placed in a cylindrical
steel container with inner diameter of 10.4 cm and inner height of 12.4 cm
filling it up to 1/3 to 2/3
15 of the height, preferable around 1/2. The steel cylinder with the mining
insert were heated with
media in a furnace to an elevated temperature of 300 C, the mining inserts
were held at the target
temperature for 120 minutes. After heating, the steel cylinder was transferred
straight into the paint
shaker and immediately shook for 2 times 5 minutes using a program without
ramping. The transfer
time between the furnace until the shaker started was less than 20 seconds.
The media (7 mm balls)
was made of a cemented carbide grade having a sintered HV20 of about 1600. The
shaking was
performed in dry conditions, i.e. no water was added to the shaking and the
samples were heated to
300 C. For all runs the inserts were left to cool down to room temperature
before they were
subjected to a final wet shaking operation for 2 x 5 min using plastic buckets
as in previous
description. None of the inventive samples had any edge damage after the post
treatment process.
Example 2 - Insert Compression test
The insert compression 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 "Hard metals ¨
Compression test" was used,
with cemented carbide anvils grade H6F from Hyperion having a 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.
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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 p.m / 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 run. 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 strength was characterized by means of the total
absorbed deformation
energy until fracture. The summary fracture energy (Ec), in Joules (J),
required to crush the samples
is shown in table 2 below:
Sample Fracture energy Ec (J)
A (comparative) 3.0
B (comparative) 8.0
C (comparative) 8.6
D (comparative) 5.0
E (invention) 8.0
F (invention) 14.5
H (comparative) 8.2
I (invention) 16.5
J (invention) 18.3
K (comparative) 5.3
L (comparative) 14.3
M (comparative) 16.2
N (comparative) 7.2
0 (invention) 15.2
S (comparative) 12.0
Table 2: Fracture energy (J) required to crush the samples
Example 3 - Hardness measurements
The hardness of the cemented carbide inserts is measured using Vickers
hardness 3 kg at
both 0.3 mm and 1.0 mm from the surface of the inserts and also in the bulk of
the inserts. The
hardness measurements are an average of 30 indentations. Table 3 shows a
summary of the
hardness measurements and table 4 shows a summary of the delta HV3 hardness
values.
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Run HV3 at the surface of the HV3 at a
depth of 1 mm HV3 bulk hardness
0.3 mm from the surface of from the surface of the measurement
the insert insert
1553.2 1526.4 1508.4
(invention)
1559.4 1529.7 1512.9
(invention)
1574.5 1564.3 1548.8
(invention)
O 1592.5 1571.0
1551.2
(invention)
O 1637.9 1614.4
1608.6
(invention)
Table 3: Hardness measurements
Run AHV3 (HV3 0.3 mm from the AHV3 (HV3 1 mm from AHV3
(HV3 0.3 mm from
surface of the insert-HV3 the surface of the insert- the
surface- HV3 1 mm
bulk) HV3 in the bulk) from the
surface)
44.8 18.0 26.8
(invention)
46.5 16.8 29.7
(invention)
25.7 15.5 10.2
(invention)
o 41.3 19.8 .. 21.5
(invention)
O 29.3 5.8 23.5
(invention)
Table 4: Delta HV3 hardness values
Example 4 - Wea r test
The samples tested in an abrasion wear test, wherein the sample tips are worn
against a
rotating granite log counter surface in a turning operation. The test
parameters used were as
follows: 100 N load applied to each insert, granite log rpm -190, log diameter
ranging from 130 to
150 mm, and a horizontal feed rate of 0.339 mm/rev. As much of the length of
the log (max 300 mm)
was used in each test to remove that difference in composition in the rock
have a significant impact
on the results. If large piece broke out from the log this area was avoided
and therefore the length in
some tests were shorter than 300 mm. The sliding distance varied due to the
difference in diameter
and length of the part of the rock that could be used but were around 330-460
m and the mass loss
versus sliding distance was approximately linear between the three samples of
each grade that was
tested. The sample was cooled by a continuous flow of water. Each sample was
carefully cleaned
and weighed prior to and after the test. Mass loss of three samples per
material was evaluated, the
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sample volume loss for each of the tested materials was calculated from the
measured mass loss
and sample density, the results are presented in table 5.
Sample Wear rate mm3/m sliding
B (comparative) 8.79x10-4
E (invention) 3.86x10-4
I (invention) 4.97x10-4
0 (invention) 2.96x10-4
Q (invention) 3.03x10-4
Table 4: Wear rates
Example 5 ¨ Fracture Toughness
Fracture toughness measurements were made according to ISO/DIS 28079 using 30
kg load
on 10 mm in diameter spherical domed samples that had been subjected to a 5
min HET treatment.
The samples were sectioned in half through the dome area, mounted in bakelite,
polished with
diamond paste and the crack length and diameter of 10 indentations 0.5 mm
below the surface
evenly distributed around the insert and at least 0.75 mm apart. The diameter
of the indentations
and the length of the cracks were measured using light optical microscope and
200 X magnification.
The K1C of each indentation was calculated using Shetty's formula K1C= A
*square root(H)/(P/Sum
of L), where H is the hardness in N/mm2, P is the applied load in N, Sum of L
is the sum of crack
length in mm, A is a constant with value of 0.0028 and K1C is given in
MPa*ma5. The average K1C
value calculated and reported as K1C_surface and the crack length and diameter
of 5 indentations in
the middle of the 10 mm inserts were measured and the average calculated and
reported as
K1C_bulk. The K1C measurement and Delta K1C-values are shown in table 5.
Sample Average K1C Average K1C_ bulk Delta K1C
surface (MPa*ma5) (MPa*m .5)
(MPa*m' )
E (invention) 16.3 11.8 4.5
I (invention) 13.7 10.9 2.8
0 (invention) 13.3 10.7 2.6
O(invention) 14.5 11.4 3.1
Table 5: K1C measurements and Delta K1C calculations
For an untreated sample delta K1C is zero or close to zero or even a slightly
negative value.
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Example 6 ¨ Field trial 1
Table 6 shows the results from a wet underground top hammer application test.
Inserts with
diameter 13 mm diameter 11 mm and with spherical shaped dome geometries were
tested. The
inserts were manufactured according to the description in example 1. The outer
diameter of all
inserts were ground. The HET-treatments of the inserts were performed
according to the description
in example 1 and the inserts were not pre-heated.
The different grades and treatments were mounted in steel bits having eight 13
mm inserts
on the periphery/gauge and three 11 mm inserts on the front. The bits were
tested in an
underground gold mine in the north of Sweden in a top hammer application. The
rock conditions
were classified as very hard and very abrasive. Before drilling started the
maximum diameter of each
bit was measured to be around 56 mm. Each bit was drilled until the inserts
were too blunt and the
penetration rate went down. The maximum diameter of the bit was then measured
again and the
difference in diameter was evaluated as wear from drilling. Another important
factor in determining
the success of the inserts is the number of insert breakage(s). Both wear and
breakage results are
shown in table 6.
No of Total Diameter Average Number of
Number of
holes drilled loss (mm) diameter
insert chipped inserts
meter wear from or broken at the
chipped at
(DM) drilling periphery/gauge
the front (3
(mm/m) (8 in total)
in total)
F (invention) 4 18 0.70 0.039 0 0
DPÃSTM 4 18 0.70 0.039 1 0
(comparative)
4 16 0.75 0.047 0 0
(comparative)
1 3.8 0.10 0.026 1 0
(comparative)
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Outside >2 6.5 n/a n/a 8 3
invention R*
Table 6. Results from the percussive drilling field test using spherical
inserts
*continued drilling with the same bit as in the row above
The results show clearly that the inventive samples have both has a good wear
resistance
and no insert chipping or breakages, which would have normally been expected
for a gamma phase
5 containing grade in a percussive drilling operation. By combining a gamma
phase containing grade
with a HET treatment the full potential of the material can be utilized, and
the performance is better
than the state of the art grade DP65TM in terms of resistance towards
chipping/insert failure and still
having the same high wear resistance. That the site is challenging to drill in
is also seen since the
sub-micron (WC) and chromium-containing grade R failed completely after only
6.3 m in operation
10 and that the prior art chromium containing grade M wears more than the
gamma phase containing
grade of the present invention.
Example 7 ¨ Field trial 2
Table 7 shows results from a wet underground top hammer application test
inserts with
diameter 8 mm diameter and 10 mm and with semi-ballistical shaped dome
geometries. The inserts
15 were manufactured according to the description in example 1. The outer
diameter of all inserts was
ground. The HET-treatments of the inserts were performed according to the
description in example
1 and the invention samples was HOTHET-treated according to the description in
example 1.
The different grades and treatments were mounted in steel bits having six 10
mm inserts on
the periphery/gauge and three 8 mm inserts on the front. Four bits/variant
were produced and
20 tested in an underground construction site in Stockholm in Sweden in a
top hammer application. The
rock conditions were classified as hard and abrasive. Before starting the
drilling, the maximum
diameter of each bit was measured and to be around 51 mm. The drilling was
started, and each bit
was used until the inserts were too blunt rate went down. The meters drilled
before the penetration
went down and the maximum diameter of the bit was then measured, and the
difference in
diameter divided by drilled meters was calculated, this provides a good
measure on the wear
resistance of the grade. In this test no insert failures were observed.
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No of Total Average Number of
bits drilled diameter insert chipped
meter wear from or broken
(DM) drilling
(mm/m)
G (invention) 4 354 0.088 0
A 4 221 0.094 0
(comparative)
Table 7. Results from the percussive drilling field test using semi-
ballistical inserts
The results show clearly that the gamma phase containing grade G (invention)
has a higher
wear resistance and can drill significantly longer before it needs to be re-
ground than the current
benchmark percussive grade A. Importantly, no insert breakages occurred for
the gamma phase
containing HOTHET treated inserts.
Example 8 ¨ Field trial 3
Table 8 shows the results from a dry (air cooled) surface top hammer
application test.
Inserts with diameter 7 mm diameter with ballistic shaped dome geometries were
tested. The
inserts were manufactured according to the description in example 1. The outer
diameter of all
inserts was ground. The HET-treatments of the inserts were performed according
to the description
in example 1 and the inserts were not pre-heated.
The different grades and treatments were mounted in steel bits having six 7 mm
inserts on
the periphery/gauge. The two front inserts in this test does not contribute to
the diameter wear and
for all bits they were in the reference grade XT49 (sample B). The bits were
tested in a stone quarry
in the south west of Sweden in a top hammer application. The rock conditions
were classified as
homogenous but very hard and very abrasive with a quartz content of about 50%
and during drilling
significantly amount of heat was generated. A rig with two hammers was used
simultaneously which
allowed a good comparison between the variants. Before drilling started the
maximum diameter of
each bit was measured on three positions (D1, D2, D3) and was around 33 mm.
Each bit was drilled
until the inserts got a significant wear but only two were drilled to end of
life (either loss of
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22
penetration rate or if insert failures occurred). Figure 2 shows a top hammer
bit with ballistic inserts
with the diameter measuring points indicated.
The maximum diameter of the bit was then measured again on all three (if no
failures)
positions and the difference in diameter was evaluated as wear from drilling.
Another important
factor in determining the success of the inserts is the number of insert
breakage(s). Both wear and
breakage results are shown in table 8.
No of Total Diameter Average Number of
holes drilled loss (mm) diameter insert
chipped
meter wear from or broken at the
(DM) drilling periphery/gauge
(mm/m) (6 in total)
0 (invention) ¨90 137.2' 0.655 0.0048 0
¨90 139.2b 0.992 0.0071 0
(comparative)
¨60 95.6 0.560 0.0059 0
(comparative)
¨110 168' 1.03 0.0061 0
(comparative)
Table 8. Results from the percussive drilling field test using ballistic
inserts
a 'b Run simultaneously one of the left hammers and one of the right hammers.
Run until end of life
The results show clearly that the inventive samples have both good wear
resistance and no
insert chipping or breakages, which would have normally been expected for a
gamma phase
containing grade in a percussive drilling operation and the wear resistance of
a gamma phase (y)+Cr
grade is even better than two high Cr-containing grades having the same binder
content and similar
room temperature hardness (HV20). By combining a gamma phase (y) + Cr
containing grade with a
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HET treatment the full potential of the material can be utilized, and the wear
resistance is
significantly better than the state of the art grade XT49T", despite that XT49
has a lower Co-content
that would be beneficial in dry (air cooled) drilling since the heat generated
is significantly higher
than in a water cooled percussive drilling.
Example 9 ¨ Field trial 4
Table 9 shows the results from a dry (air cooled) surface top hammer
application test.
Inserts with diameter 7 mm diameter with ballistic shaped dome geometries were
tested. The
inserts were manufactured according to the description in example 1 and the
inventive sample, I,
had a gamma phase free zone of about 20 microns after sintering, which will
wear off quickly during
drilling or be ground away during the outer diameter grounding. The outer
diameter of all inserts
was ground. The HET-treatments of the inserts were performed according to the
description in
example 1 and the inserts were not pre-heated.
The different grades and treatments were mounted in steel bits having six 7 mm
inserts on
the periphery/gauge. The two front inserts in this test does not contribute to
the diameter wear and
for all bits they were in the reference grade XT49 (sample B). The bits were
tested in a stone quarry
in the south west of Sweden in a top hammer application. The rock conditions
were classified as
homogenous but very hard and very abrasive with a quartz content of about 50%
and during drilling
significantly amount of heat was generated. A rig with two hammers was used
simultaneously which
allowed a good comparison between the variants. Before drilling started the
maximum diameter of
each bit was measured on three positions (D1, D2, D3) and was around 33 mm.
Each bit was drilled
until the inserts got a significant wear. The maximum diameter of the bit was
then measured again
on all three (if no failures) positions and the difference in diameter was
evaluated as wear from
drilling. Another important factor in determining the success of the inserts
is the number of insert
breakage(s). Both wear and breakage results are shown in table 9.
No of Total Diameter Average Number of
holes drilled loss (mm) diameter insert
chipped
meter wear from or broken at the
(DM) drilling periphery/gauge
(mm/m) (6 in total)
I (invention) ¨30 512 0.42 0.0082 0
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¨30 Slb 030 0.0099 0
(comparative)
Table 9. Results from the percussive drilling field test using ballistic
inserts
am Run simultaneously one of the left hammers and one of the right hammers.
The results show that the inventive sample I, despite having a quite high
gamma phase
content also including Ti and nitrogen ((Ti, Ta, Nb, W)(C,N)) had enough
toughness & strength from
the HET-treatment to be used in a percussive drilling application in a very
sensitive ballistic insert
geometry. Sample I also showed an improved wear resistance compared to the
state of the art
grade XT49r" (sample B), despite that XT49 has a lower Co-content that would
be beneficial in dry
(air cooled) drilling since the heat generated is significantly higher than in
a water cooled percussive
drilling.
15
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