OA20726A - Method of treating a mining insert. - Google Patents

Abstract

The present invention relates to a method of treating a sintered mining insert comprising cemented carbide wherein said mining insert is subjected to a surface hardening process, characterized in that the surface hardening process is executed at an elevated temperature of or above 100°C. The invention further relates to a mining insert wherein the HV1 Vickers hardness measurement increase (HV1%) from the surface region, measured as an average of HV1 measurements taken at 100 µm, 200 µm and 300 µm below the surface, compared to the HV1 Vickers hardness measured in the bulk (HV1bulk) is at least 8.05 - 0.00350 x HV1bulk.

Description

The présent invention is related to a method of treating a cemented Carbide mining insert wherein post sîntering the mining insert is subjected to a surface hardening process at an elevated 5 température and a cemented carbide mining insert treated according to this method.

BACKG ROUND

Cemented carbide has a unique combination of high elastic modulus, high hardness, high compressive strength, high wearand abrasion résistance with a good level of toughness. Therefore, cemented carbide is commonly used in products such as mining tools. Cemented carbide mining inserts are commonly treated with an edge deburring and surface hardening process, such as tumbiing, post sintering and centreless grinding. The surface hardening process introduces compressive stress into the mining inserts. The presence ofthe compressive stresses improves the fatigue résistance and fracture toughness ofthe mining insert. Consequently, the threshold energy necessary to fracture the mining insert is higher and so there is a reduced likelihood of chipping, cracking and / or fracture of the component. Therefore, it is désirable to increase the level of compressive stress introduced into the mining insert to increase the lifetime of the insert.

High energy tumbiing (HET) methods such as those disclosed in US7258833B2 provide a way to increase the level of compressive stresses introduced, however there it is désirable to be able to improvethis process further by providing a method that can introduce even higher levels ofthe compressive stresses into the mining inserts without damaging them.

It is an object of the présent invention to provide a method of introducing higher levels of compressive stress into a cemented carbide mining insert keeping the damage level down.

SUMMARY OF INVENTION

Thus, the présent disclosure provides a method of treating a sintered mining insert comprising cemented carbide wherein said mining insert is subjected to a surface hardening process, characterized in that the surface hardening process is executed at an elevated température of or above 100°C, preferably at a température of or above 200°C, more preferably at a température of between 200°C and 450°C.

The advantage ofthe présent method is that higher levels of compressive stresses are introduced into the cemented carbide mining insert. An elevated tumbiing température results in increased toughness ofthe Carbide and hence the collisions do not resuit 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 résistance and fracture toughness ofthe mining insert and consequently încrease 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 tumbling. The method also makes it possible to use cemented Carbide compositions that would hâve previously been too brittle for mining applications or for high energy tumbling described in U57258833B2, Epiroc Smith, for example, inserts having a high level of eta-phase or lower binder content. Increasing the surface treatment process température from room température up to températures such as 300 °C, results in a hardness drop of more than 200 HV20, which gives rise to a toughness încrease. The ability to introduce higher levels of compressive stress means that the toughness ofthe mining inserts is increased to an acceptable level and thus mining inserts having a higher hardness can be used which is bénéficiai for increasing the wear résistance ofthe mining inserts.

Additionally, the présent disclosure provides a mining insert, wherein the HV1 Vickers hardness measurement încrease (HV1%) from the surface région, measured as an average of HVl measurements taken at 100 pm, 200 pm and 300 pm below the surface, compared to the HVl Vickers hardness measured in the bulk (HVlbulk) is at least HV1% > 8.05-0.0035 x HVlbulk.

The advantage of this is that the crush strength ofthe mining insert is increased, which therefore leads to an increased lifetime ofthe mining insert.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1: HVl maps for surface and bulk hardness measurements.

Figure 2: Plots showing the HV1% trend lines.

DETAILED DESCRIPTION

According to one aspect ofthe présent invention is a method of treating a sintered mining insert, comprising cemented Carbide wherein said mining insert is subjected to a surface hardening process, characterized in that the surface hardening process is executed at an elevated température of or above 100°C, preferably at a température of or above 200°C, more preferably at a température of between 200°C and 450°C.

By cemented Carbide'' is herein meant a material that comprises at least 50 wt% WC, possibly other hard constîtuents common in the art of making cemented carbides and a metallic binder phase preferably selected from one or more of Fe, Co and Ni. In one embodiment ofthe method, the cemented Carbide mining insert contains a hard phase comprising at least 80 wt% WC, preferably at least 90 wt%.

The metallic binder of the cemented carbide can comprise other éléments that are dissolved in the metallic binder during sintering, such as W and C originating from the WC. Depending on what other types of hard constîtuents that are présent, also other éléments can be dissolved în the binder.

A surface hardening treatment is defined as any treatment that introduces compressive stresses into the material through physical impacts, that results in deformation hardening at and below the surface, for example tumbling orshot peening. The surface hardening treatment is done post sintering and grinding. It has unexpectedly been found, that treating a mining insert with a surface hardening treatment at elevated températures decreases or even éliminâtes the carbide to carbide collision damages in terms of chipping and micro fracturing and therefore improving product lifetime. The surface hardening process of the présent invention is performed at an elevated température, and this température is herein defined as the température ofthe mining insert at the start ofthe surface hardening process. The upper limlt forthe température, where the surface hardening process is performed, is preferably below the sintering température, more preferably below 900°C. The température ofthe mining insert îs measured by any method suitable for measuring température, such as an infrared température measurement.

In one embodiment ofthe présent invention the mining insert is subjected to a surface hardening treatment at a température of between 150’250°C, preferably at a température of between 175-225’C.

In one embodiment ofthe présent invention the upper limlt for the surface hardening treatment is 700°C, preferably 600°C, more preferably S50°C.

In one embodiment ofthe présent invention the mining insert is subjected to a surface hardening treatment at a température of between 300-600°C, preferably at a température of between 350-550’C, more preferably of between 450-550°C.

The température is measured on the mining insert using any suitable method for measuring température. Preferably, an infrared température measurement device is used.

In one embodiment the cemented Carbide comprises hard constituents in a metallic binder phase, and wherein the metallic binder phase content in the cemented Carbide is 4 to 30 wt%, preferably 5 to 15wt%.

The binder phase content needs to be high enough to provide a tough behaviour of the 5 mining insert. The metallic binder phase content is preferably not higher than 30wt%, preferably not higher than 15 wt%. A too high content of binder phase reduces the hardness and wear résistance of the mining insert. The metallic binder phase content is preferably greater than 4wt%, more preferably greater than 6wt%.

In one embodiment metallic binder phase comprises at least 80wt% of one or more metallic 10 éléments selected from Co, Ni and Fe.

Preferably Co and / or Ni, most preferably Co, even more preferably between 3 to 20wt% 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% ofthe binder content. The grain refiner compound is suitably selected from the group of carbides, mixed carbides, 15 carbonitrides or nitrides of vanadium, chromium, tantalum and niobium. With the remainder ofthe

Carbide mining insert being made up of the one or more hard-phase components.

In one embodiment the cemented Carbide additionally comprises Cr, in an amount such that the mass ratio of Cr/binder is of 0.043 -0.19.

The mass ratio ofthe Cr/binder is calculated by dividingthe weight percentage (wt%) ofthe 20 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 dissotved 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 préférable to only add Cr up to the mass ratio of Cr/binder so that ail the Cr dissolved into the binder so that the sintered cemented carbide body is free of undissolved chromium carbides.

The mass ratio of Cr/binder could be between 0.043 - 0.19 preferably between 0.075 - 0.15, more preferably between 0.085 - 0.12. If the mass ratio of Cr/binder is too low, the positive effects of the Crwill be too small. If, on the other hand, the mass ratio ofthe Cr/binder is too high, there 30 will be an increased formation in the concentration of chromium carbides, in which the binder will dissolve, thereby reducing the volume of the binder phase and consequently making the cemented carbide body too brittle.

The Cr is normally added to the powder blend in the form of Cr₃C₂ as this provides the highest proportion of Cr pergram of powder, although it should be understood that the Cr could be added to the powder blend using an alternative chromîum Carbide such as Cr₂₆C₂ or Cr₇C₃ or a chromium nitride.

The addition ofthe Cr also has the effect of improving the corrosion résistance ofthe cemented Carbide body. The presence of the Cr also makes the binder prone to transform from fcc to hep during drilling, this is bénéficiai 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 résistance of the cemented Carbide and increase its ability for deformation hardening. The combination of the Cr in the cemented Carbide powder and the application ofthe powder comprising a grain refîner compound and optionally a carbon-based grain growth promoter, to at 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 résistance.

Apart from the hard-phase forming component, the binder and Cr containing component, incidental impurities may be present in the WC-based starting material.

In one embodiment ofthe présent invention, the cemented Carbide before being subjected to the surface hardening treatment has a bulk hardness between 1200 - 1900 HV1, preferably between 1300 - 1850 HVl, most preferably between 1400 -1700 HV1.

In one embodiment ofthe present invention, the cemented Carbide is not coated.

In one embodiment of the present invention, the cemented Carbide comprises M₇C₃ carbides, and possibly also M₃C₂ carbides, where M is Cr and possibly one or more of W, Co and any other éléments added to the cemented carbide. By that is herein meant that the M?C₃ carbides should be clearly visible in a SEMI (scanning électron microscope) image using backscattering at a magnification enough to detect particles of a size of 100 nm. In one embodiment ofthe present invention, the cemented carbide comprises MI7C3 carbides in an amount given by the ratio vol% M?C₃ carbides/vol% Co. Suitably the ratio vol% M₇C₃ carbides/vol% Co is between 0.01 to 0.5 preferably between 0.03 to 0.25. The vol% of MI₇C3 carbides and the Co binder can be measured by EBSD or image analysis using a suitable software.

In one embodiment, the cemented carbide has a Com/Co ratio 0.75 < Com/Co<0.98. Corn is magnetic saturation in weight % and Co is the weight percentage of cobalt in the cemented

Carbide. Com is related tothe magnetic saturation 4τιοι [uTm³/kg] ofthe cemented Carbide to the magnetic saturation for pure metallic Co binder 4πσ_ο=2Ο1.9 [pTmVkg] through the équation:

Com(%) = 4πσι*(100/201.9)

Reference: Measurement Good Practice Guide No. 20 by Roebuck et al. 1999 NPL

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/Coi0.98. 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 ail magnetic moments inside the material. A Foerster KOERZIMAT 1.096 is used to détermine the magnetic saturation (Com) dipole moment jS and the derived weight spécifie saturation magnetization oS (4rto) ofthe 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 în the binder increases with decreaslng 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 bénéficiai 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 another embodiment of the présent invention, the cemented Carbide substrate comprises eta phase comprising Me^C and/or MeaC carbides where Me is one or more metals selected from W, Mo and the binder phase metals. The cemented carbides hâve a Com/Co ratio < 0,69. If other constituents are added e.g. grain growth inhibitors, gamma phase formers etc to the cemented Carbide, the Com/Co ratio will be influenced. The eta phase formed is, however, not présent as large agglomérâtes. Commonly, eta phase has been considered as unwanted in cemented Carbide due to that it has traditionally been présent in large agglomérâtes of eta phase grains, which are brittle and detrimentai to the cemented Carbide properties. The cemented Carbide according to this embodiment ofthe présent invention, should hâve an evenly distributed eta phase, by that is herein meant that the cemented Carbide is free from large agglomérâtes. The amount of eta phase is at least 2 vol%, preferably at least 4 vol%. By providing the non-agglomerated eta phase by selecting a certain range of sub-stoichiometric carbon content as in the cemented Carbide of this embodiment,

the cemented Carbide shows good properties. The eta phase is présent in the microstructure as a fine dispersed phase. Common carbides ofthe eta phase are W_sCo₆C, W3C03C, W₆Ni₆C, W₃Ni₃C, WeFesC, W₃Fe₃C. In one embodiment the eta phase comprises both Me^C and MeeC.

In one embodiment the method additionally includes a step wherein prior to sintering a liquid dispersion or slurry comprising a grain refiner and carbon and/or nitrogen, and a grain growth promoter being carbon, is applied to least one portion of the surface of a compact of the cemented Carbide, the grain refiner compound and the grain growth promoter are both provided onto the surface or surfaces in an amount of from 0.1 to 100 mg/cm².

The grain refiner compound is a Carbide, mixed Carbide, carbonitride or a nitride, the grain refiner compound and grain growth promoter is provided on the surface ofthe compact by first providing a compact and then providing the grain refiner compound and the grain growth promoter on at least one portion ofthe surface ofthe compact, the grain refiner compound and grain growth promoter is provided by application in the form of a separate or combined liquid dispersion or slurry to the compact, the weight ratio of grain refiner compound to grain growth promoter is from about 0.05 to about 50. The compact is sintered after the grain refiner compound and grain growth promotor hâve been applied to the surface ofthe compact priorto the surface hardening treatment.

The grain refiner compound is preferably a Carbide or nitride of chromium or vanadium. Further details on the method for applying the grain refiner compound and grain growth promoter to the surface of the cemented carbide compacts can be found in EP2355948B1.

In one embodiment the method includes a step of heating the minîng inserts and media prior to the surface hardening process and the surface hardening process is performed on heated mining inserts.

The mining insert can be heated in a separate step prior to the surface hardening process step. Several methods can be used to create the elevated température of the mining insert, such as induction heating, résistance heating, hot air heating, flame heating, pre-heating on a hot surface, in an oven or furnace or using laser heating.

In an alternative embodiment, the mining inserts are kept heated during the surface hardening process. For examples using an induction coil.

In one embodiment after the mining inserts hâve been subjected to the surface hardening process at an elevated température, the mining inserts are subjected to a second surface hardening process at room température. Advantageously, this removes débris and oxides, for example iron oxide, that are deposited on the însert surfaces from the inside ofthe process container. The second surface hardening process performed at room température could be performed in wet conditions, which will aid in removing dirt and dust from the mining inserts being treated which reduces health hazards.

In one embodiment the surface hardening process is tumbling. The tumbling treatment could be centrifugal or vibrational. 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 about 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 dise at the bottom. One more method is the centrifugal barrel finishing process. In both centrifugal processes, the rotation causes the inserts to collide with other inserts or with any media added. For standard tumbling using a centrifugal tumbler the tumbling operation would typically be run from 120 RPM for at least 20 minutes. The lining of the tumbler may form oxide or métal deposits onto the surface ofthe inserts.

It may be necessary to modify the lining of the tumbler to be able to withstand the higher elevated températures that the process is conducted at.

In one embodiment the tumbling process is a High Energy Tumbling (HET) process, wherein post tumbling a homogenous cemented Carbide mining insert has been deformation hardened such that ÛHV3% > 9.72 -0.00543*HV3b_Uik, wherein the ÛHV3% is the percentage différence between the HV3 measurement at 0.3 mm from the surface compared the HV3 measurement in the bulk.

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 spécifie degree of deformation hardening in a homogenous cemented carbide mining insert consisting of WC-Co, having a mass of about 20g. In the présent disclosure, HET is defined as a tumbling treatment that would introduce a hardness change, measured using HV3, after tumbling (AHV3%) of at least:

AHV3% = 9.72 - 0.00543* HV3_buik (équation 1)

Wherein:

AHV3% = 100*(HV3o.3_mm - HV3_buik)/HV3b_Uik (équation 2)

HV3_bUik is an average of at least 30 indentation points measured in the innermost (centre) of the cemented Carbide mining insert and HV3o.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 équations (1) and (2) on a homogenous cemented Carbide mining insert would be applied to cemented Carbide bodies having a gradient property.

HET tumbling may typically be performed using an ERBA 120, having a dise 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 Rosier tumbler, having a dise 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.

In one embodiment the tumbling process is conducted in dry conditions. The effect of the surface hardening treatment at elevated températures is en ha need if the process is done in dry conditions. By dry conditions it is meant that no liquid is added to the process. Without being found by this theory, it is thought that, if liquid is introduced to the process, it will lower the température of the parts. Further, the inclusion of the liquid will reduce the degree of the impact between the parts being tumbling. The internai friction will generate and preserve heat.

The tumbling process could be conducted in the presence or absence of tumbling media depending on the geometry and material composition of the mining inserts being tumbled. If it is decided to add tumbling media, the type and ratio of media to inserts is selected to suit the geometry and material composition of the mining inserts being tumbled.

Optionally, ail or part of the heat is generated by friction between the inserts and any media added in the tumbling process.

Optionally, the inserts are furthersubjected to a second surface hardening process. Preferably, if a second surface hardening process performed at room température is done, this second surface hardening process is HET tumbling at room température in wet condition.

In one embodiment the mining insert treated with a surface hardening process at elevated température has a HVl Vickers hardness measurement increase (HV1%) from the surface région, measured as an average of HVl between 100-300pm below the surface, compared to the HVl Vickers hardness measured in the bulk (HVlbulk) is at least HV1% > 8.05 - 0.00350 x HVlbulk, preferably HV1% > 8.45 -0.00355 x HVlbulk. Preferably, HV1% < 17.5-0.00662 x HVlbulk. This is shown in figure 2.

By the term bulk is herein meant the innermost part (centre) of the cutting tool and for this disclosure is the zone having the lowest hardness.

The hardness ofthe cemented Carbide înserts is measured using Vickers hardness automated measurement. The cemented Carbide bodies are sectioned along the longitudinal axis and polished using standard procedures. The sectioning is done with a diamond dise cutter under flowing water. Vickers indentations at a 1 kg load are then equidistantly distributed over the polished section at the given depths below surface. The hardness of the surface zone is an average of about 180 indentations taken at the given distances 100, 200 and 300pm below the surface. The hardness of the bulk is an average of about 150 indentations taken at the given distances 4.50, 4.65 and 4.80mm below the surface. Figure i shows the HVl layout where the filled squares represent the locations surface indications 2 and the bulk indications 4.

The hardness measurements are performed using a programmable hardness tester, KB30S by KB Prüftechnik GmbH calibrated against HVl test blocks issued by Euro Products Calibration Laboratory, UK. Hardness is measured according to 1SO EN65O7.

HVl measurements were done în the following way:

Scanning the edge ofthe sample.

Programming the hardness tester to make indentations at specified distances from the edge ofthe sample.

Indentation with 1 kg load at ail programmed co-ordinates.

The computer moves the stage to each co-ordinate, locates the microscope over each indentation, and runs auto adjust light, auto focus and the automatically measures the size of each indentation.

The user inspects ail the photos ofthe indentations for focus and other matters that distu rb the resuit.

In one embodiment the residual stress of 20 g mining insert post the surface hardening process at an elevated température is at least 1250 MPa.

” The residual stress measurements were analyzed using X-ray diffraction on the insert top by using a Bruker D8 Discovery with Cu Ka (1.54Â) with a parallel beam poly-capillary and with a coliimator with 0.5mm aperture.

The measurement was performed using the iso-inclination method (5ίη2ψ method) at 11 5 different ψ angles from -45 to 45 ’ and 3 different φ at 0,45 and 90 °. The élongation was calculated for peak displacements for the Bragg peak with hkl: 311 (117.32 ’ 2Θ). For the calculation ofthe residual stresses, the software Leptos (Bruker) was used. The input values for the calculations were 65OMPa for the E-module and 0.19 for Poisson's constant. Since we assume that there is no directional dependence on the residual stresses, a normal voltage mode) (not biaxial) was used.

And the measurements at the 3 φ angles for each sampie are considered as individual measurements. The diffractometer is continuously checked with a corundum sampie (NIST standard) to ensure alignment.

EXAMPLES

Example 1 -Starting materials and tumbling conditions

Mining inserts with different compositions (based on the starting composition of the powders weighed in to the milled) were tested. Table 1 shows the summary ofthe compositions of the mining inserts tested:

Mining insert composition	WC (wt%)	Co (wt%)	Cr (wt%)	Com/Co	HV1 (bulk)	HV20 (bulk)	Dipped in slurry?
A	94	6.0	0	0.92	1488	1470	No
B	93.4	6.0	0.6	0.78	1450	1420	No
C	94	6.0	0	0.61	1540	1510	No
D	94	6.0	0	0.77	1500	1520*	Yes
E	94	6.0	0	0.83	1558	1530	No
F	89	11	0	0.95	1165	1120	No
G	95	5.0	0.5	0.81	1397	1380	No

Table 1: Composition of mining inserts tested. * measured 0.5mm below the tip since D is a gradient.

Sampie A, E and F represent a standard cemented carbide grades used for mining inserts.

Samples B and G contain chromium and sampie C contains eta phase. Ail cemented carbide inserts were produced using a WC powder grain size measured as FSSS was before milling between 5 and 18

um. The WC and Co powders were milled in a bail mill in wet conditions, using éthanol, with an addition of 2 wt% polyethylene glycol (PEG 8000) as organic binder (pressing agent) and cemented carbide milling bodies. After milling, the mixture was spray-dried in Nî-atmosphere and then uniaxially pressed into mining inserts having a size of about 10 mm in outer diameter (OD) and about 17-20 mm in height with a weight of approximately 20g each with a spherical dôme (cutting edge) on the top, The samples were then sintered using Sinter-HIP in 55 bar Ar-pressure at 1410°Cfor 1 hour, Sample D is the same starting material as sample A, but prior to sintering the samples were dipped in a slurry comprising 25 wt% Cr₃C: and 5 wt% graphite dispersed in water applied to the surface ofthe cemented carbide mining insert so that about 60% ofthe total insert length was exposed to the slurry.

For comparison a batch of 25 or 50 of each of the samples A-D was treated using a HET centrifugal tumbling process at 25°C (room température) in a Rosier FKS04 tumbler at 300RPM for 50 minutes with 50kg of 7mm carbide balls of grade H10F in wet conditions. In the tables ofthe results samples treated according to this method is referred to as 25°C wet HET.

In order to replicate tumbling at an elevated température on a lab scale a hot shaking method has been used. The hot shaking method uses a commercially available paint shaker of trade mark Corob™ Simple Shake 90 with a maximum load of 40 kg and a maximum shaking frequency of 65 Hz. The hot shaking method was conducted in batches of 50 mining inserts at a frequency of 45 Hz. About 800grams or 50 pièces of inserts and 4.2kg carbide media (1560 pièces of about 7mm balls) where placed in a cylindrical Steel container with inner diameter of 10cm and inner height of 12cm fîlling it up to 2/3 of the height. The Steel cylinder with the mining insert were heated with media in a furnace to an elevated température of 100, 200 or 300°C, the mining inserts were held at the target température for 120 minutes. After heating, the Steel cylinder was transferred straight into the paint shaker and immediateîy shook for 9 minutes. The transfer time between the furnace until the shaker started was less than 20 seconds. The media was made of the cemented carbide grade H10F having 10wt%Co,0.5 wt%Grand 89.5 wt% WCthat results insintered HV20 of about 1600. In the tables of results samples treated according to this method are referred to as 100°C dry shake, 200°C dry shake or 300°C dry shake depending on the température used. The shaking was performed in dry conditions, i.e. no water was added to the shaking. Some samples were also treated by shaking in dry conditions at toom température, in the table of results this method is referred to as 25°C dry shake. Forthese samples the 25°C dénotés the température at the start of the treatment, however due to friction and collision heat formed during the 9-minute shaking process the final température in the Steel cylinder is actually between GO-lOO’C, i.e. also elevated.

Following the shaking the samples were then cooled down and treated using the HET centrifugal tumbiing process described above as well as a second surface hardening process. In the tables of resuits samples treated according to this method are referred to as 300’C shake dry + 25 °C H ET wet.

Example 2 - Edge damage

It is important that the damage to the edges of the mining inserts is low, preferably none at ail, post tumbiing in order to hâve the highest yields.

The mining inserts were inspected visually for damages post tumbiing for to compare the yields ofgood quality mining inserts if the surface hardening treatment is done at room température vs 300°C. The mining insert was counted as having damage if the chipping was greater than about 1mm in length or if the chipping reached out to the centreless ground cylindrical surface of the insert. The percentage of damaged inserts reported in table 2:

Mining insert composition	Surface hardening treatment
25Τ shake wet (100ml water added) (comparison)	25°C dry shake (invention)	100°C shake dry (invention)	2Û0°C shake dry (invention)	300°C dry shake (invention)
A	10%	6%	4%	4%	0%
8	26%	4%	0%	2%	0%
C	96%	70%	68%	50%	8%
D		0%	0%	0%	0%

Table 2: Percentage of mining inserts being damaged post shaking treatment.

The températures stated for the surface hardening treatments are starting températures.

For the batches treated with a starting température of 25°C, if water is added to the process, the température is not expected to significantly increase as the samples are treated, where for the samples treated in dry conditions, there will be an increase in température as heat is generated by friction between the inserts and the media in the tumbiing process. The resuits in table 2 show that there is a réduction in the amount of edge damage to the mining inserts if the surface hardening treatment is conducted at an elevated température.

Example 3 - 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 ofthe 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.

The loading axis was identical with the axis of rotational symmetry ofthe inserts. The counter surfaces ofthe fixture fulfilled the degree of parallelism required in the ISO 4506:2017 (E) standard, i.e. a maximum déviation of 0.5 pm / mm. The tested inserts were loaded at a constant rate of crosshead displacement equai to 0.6 mm / min until failure, while recording the loaddisplacement curve. The compliance ofthe test rig and test fixture was subtracted from the measured load-displacement curve before test évaluation. Five 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. Subséquent inspection of tested inserts confirmed that this in ail 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 summary fracture energy, in Joules (J), required to crush the samples is shown in table 3 below:

Mining insert composition	Surface hardness treatment
25°C wet HET (comparison)	300°C dryshake (invention)	300°C dry shake + 25 °C wet HET (invention)
A	9.28	10.5	12.0
8	9.37	10.5	14.2
C	8.62	10.1	12.1
D	7.74	9.85	11.3
E	1.61	-	2.57
F	6.91	9.27	10.8
G	6.94	8.86	10.2

Table 3: Fracture energy (J) required to crush the samples (Grade E was tested with a 2.5mm tip radius while ail other grades were tested with a 5mm tip radius.)

It can be seen that there is an increase in fracture energy for ail samples when the surface hardening treatment is conducted at an elevated température compared to at room température.

Example 4 - Field trial

Top hammer bits were made having an initial bit diameter of about 49 mm with six peripheral inserts of 10mm diameter and three front inserts of 9mm. The insert geometry was conical with a spherical top of 2.5mm radius.

Two bits were tested with each of the following type of inserts: Sample A, treated according to the standard centrifugal method 25°C wet HET surface hardening treatment, this represents standard inserts that wouid be used for top hammer drilling; Sample E, treated according to the

25°C wet HET surface hardening treatment, this material wouid generally considered too brittle and unsuitable for top hammer drilling; Sample E, treated according to the 300°C dry shake + 25°C wet HET” surface hardening treatment, and is the inventive sample. The bits were tested on granodiorite rock in the Sandvik Test Mine in Myllypuro, Finland. The drill rig was equipped with a HLX5 rock drill operating at full power which means percussive pressure 200 bar, feed pressure at

100 bar, rotation at 240 RPM and rotation pressure at 120 bar. The bits are classed as having failed if either the bit breaks or the bit wouid need re-sharpening before drilling could be continued. The average results from the two bits (per case) are shown in table 4 below:

Mining insert composition	Surface hardening treatment	Drilled depth before worn out (métrés)	Bit diameter loss (mm)	Drilled meters per mm of bit diameter lost (m/mm)
A (comparative)	25°C wet HET	236	0.81	291
E (comparative)	25’C wet HET	47	Bits broke	-
E (inventive)	300°C dry shake + 25°C wet HET	289	0.85	340

Table 4: Field trial results

It can be seen that by applying the surface hardening treatment at an elevated température 20 the drilling performance is improved for the inventive sample compared to the standard material used for top hammer drilling (sample A heated according to the conventional method 25°C wet HET) even for an insert grade, E, that wouid normally perform very badly if the surface hardening treatment is performed only at room température.

Example 5 - Hardness measurements

Hardness measurements were made according to the description explained hereînabovefor the samples described in table 1. HV1 hardness was measured in the bulk (values in table 1) and at depths of 100, 200 and 300 pm below the surface of lengthwise cross sectioned samples and the percentage of hardness increase compared to the bulk is reported în table 5 for the samples treated according to the 300°C dry shake + 25°C wet HET surface hardening method.

Mining insert composition	Depth below the surface
100 pm	200 pm	300 pm
A	4.66	4.05	3.33
B	6.93	4.36	3.1
C	3.93	3.28	2.89
D	9.29	7.99	6.77

Table 5: Percentage increase in HV1 at different depths below the surface compared to the bulk

It can be seen that for ail cases the there is an increase in HV1 at the surface of the mining insert compared to în the bulk.

Example 6 - Residual stress measurements

Residual stress measurements were made on the samples according to the method described hereinabove. Table 6 shows that the residual stress in the samples is higher after a post tumbling treatment at an elevated température compared to a post tumbling treatment at room température.

Mining insert composition	Surface hardening treatment
25°C wet HET (comparison)	300°C dry shake + 25°C wet HET (invention)
A	1340	1386
B	1389	1610
C	1584	1564
D	1324	1415

Table 6: Compressive stress measurements (Mpa)

Claims (20)

1. A method of treating a sintered mining insert comprising cemented Carbide wherein said mining insert is subjected to a surface hardening process, characterized in that the surface hardening process is executed at an elevated température of or above 100°C.

2. The method according to claim 1, wherein the elevated température is above 200°C.

3. the method according to claim 2, wherein the elevated température is between 200°C and

450°C.

4. The method according to any of the previous daims, wherein the cemented Carbide comprises hard constituents in a metallic binder phase, and wherein a metallic binder phase content in the cemented Carbide is 4 to 30 wt%.

5. The method according to claim 4, wherein the metallic binder phase content In the cemented Carbide is 5 to 15wt%.

6. The method according to claim 4 or claim 5, wherein the metallic binder phase comprises at least 80wt% of one or more metallic éléments selected from Co, Ni and Fe.

7. The method according to any of the previous daims, wherein the cemented carbide additionally comprises Cr, in an amount such that a mass ratio of Cr/binder of the metallic binder phase is 0.043 -0.19.

8. The method according to any of the previous daims wherein the cemented Carbide comprises M₇C₃ carbides.

9. The method according to any of the previous daims, wherein the cemented carbide has a Com/Co ratio: >0.75 and <0.98.

10. The method according to any of daims 1-8, wherein the cemented carbide has a Com/Co ratio <0.69 and at least 2% volume eta phase.

11. The method according to any ofthe previous daims, wherein priorto sintering, a liquid dispersion or slurry comprising a grain refiner compound comprising a grain refiner and carbon and/or nitrogen, and a grain growth promoter being carbon, is applied to least one portion of the surface of a compact ofthe cemented carbide, the grain refiner compound and the grain growth promoter both being provided onto the surface or surfaces in an amount of from 0.1 to 100 mg/cm².

12. The method according to any of the previous daims, wherein the method includes a step of heating the mining insert and any media présent priorto the surface hardening process, and the surface hardening process is performed on the heated mining insert.

13. The method according to any ofthe previous daims, wherein the mining insert is kept heated during the surface hardening process.

14. The method according to any of the previous daims, wherein after the mining insert has been subjected to the surface hardening process at an elevated température, the mining insert is subjected to a second surface hardening process at room température.

15. The method according to any ofthe previous daims, wherein the surface hardening process is tumbling.

16. The method according to claim 15, 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 AHV3% > 9.72 - 0.00543*HV3butk, wherein the ÛHV3% is the percentage différence between the HV3 measurement at 0.3 mm from the surface compared the HV3 measurement in the buik.

17. The method according to any of daims 15-16, wherein the tumbling process is conducted in dry conditions.

18. The method according to any of daims 15 to 17, wherein ali or part of the heat is generated by the friction between the insert and any media added în the tumbling process.

19. A mining insert produced according to the method of any of daims 1-18, wherein the HV1 Vickers hardness measurement increase (HV1%) from the surface région, measured as an average of HV1 measurements taken at 100 pm, 200 pm and 300 pm below the surface, compared to the HV1 Vickers hardness measured in the bulk (HVlbulk) is at least 8.05 -0.00350 x HVlbulk.

20. A mining insert according to claim 19, wherein HV1% is < 17.5 - 0.00662 x HVlbulk.