Method for processing a mining insert

Abstract

The present invention relates to a method for treating sintered mining inserts comprising cemented carbide, characterized in that the mining inserts are subjected to a surface hardening treatment, the surface hardening treatment being carried out at an elevated temperature of at least 100° C. The present invention further relates to a mining insert having a percentage increase in HV1 Vickers hardness measurement in the surface area (HV1%) compared to the HV1 Vickers hardness measured in the bulk (HV1 Bulk), measured as the average of HV1 measurements taken 100 μm, 200 μm and 300 μm below the surface, of at least 8.05-0.00350 x HV1 Bulk.

Description

Technical Field

[0001] The present invention relates to a method for treating a cemented carbide mining insert, which comprises subjecting the sintered mining insert to a surface hardening treatment at a high temperature after sintering, and to a cemented carbide mining insert treated according to this method.

Background Art

[0002] Cemented carbide has a unique combination of high elastic modulus, high hardness, high compressive strength, high wear resistance, and a good level of toughness. Therefore, cemented carbide is commonly used in products such as mining tools. Cemented carbide mining inserts are generally processed by edge deburring, surface hardening treatment, for example, tumbling, centerless grinding after sintering. In the surface hardening treatment, compressive stress is introduced into the mining insert. The presence of compressive stress improves the fatigue resistance and fracture toughness of the mining insert. As a result, the threshold energy required to fracture the mining insert becomes higher, so the possibility of chipping, cracking, and / or fracturing of the component is reduced. Therefore, in order to extend the life of the insert, it is desirable to increase the level of compressive stress introduced into the mining insert.

[0003] The high energy tumbling (HET) method as disclosed in U.S. Patent No. 7,258,833 provides a method for increasing the level of compressive stress introduced, but it is desirable to further improve this process by providing a method that can introduce an even higher level of compressive stress into the mining insert without damaging the mining insert.

[0004] An object of the present invention is to provide a method for introducing a high level of compressive stress into a cemented carbide mining insert while maintaining a low damage level.

Summary of the Invention

[0005] Accordingly, the present disclosure provides a method for treating a sintered mining insert comprising a cemented carbide, the method comprising subjecting the mining insert to a surface hardening treatment, the surface hardening treatment being carried out at a high temperature of 100 °C or higher, preferably at a temperature of 200 °C or higher, more preferably at a temperature of 200 °C to 450 °C.

[0006] An advantage of this method is that a higher level of compressive stress is introduced into the cemented carbide mining insert. As the tumbling temperature increases, the toughness of the cemented carbide improves, and thus, defects such as microcracks, large cracks, or edge chipping do not occur due to collisions. The higher level of compressive stress, combined with the reduction of collision defects, improves the fatigue resistance and fracture toughness of the mining insert, resulting in an extended insert life. A further advantage of this method is that insert shapes that were previously prone to excessive damage at the corners and thus had a low yield, such as shapes with a sharp groove bottom radius, can be tumbled without causing edge damage. This opens up the possibility of developing mining insert products with various geometric shapes that were previously not suitable for tumbling. This method also enables the use of cemented carbide compositions that were previously too brittle for mining applications or high-energy tumbling, such as those described in U.S. Patent No. 7,258,833 to Epiroc Smith, for example, inserts with a high level of eta phase or a lower binder content. Increasing the surface treatment process temperature from room temperature to a temperature such as about 300 °C results in a hardness reduction exceeding 200 HV20 and an increase in toughness. The ability to introduce a higher level of compressive stress means that the toughness of the mining insert can be increased to an acceptable level, and thus, mining inserts with a higher hardness, which is effective in enhancing the wear resistance of the mining insert, can be used.

[0007] Furthermore, the present disclosure provides an excavation insert in which the increase rate of the HV1 Vickers hardness measurement value (HV1%) from the surface region, measured as the average value of the HV1 measurement values obtained at 100 μm, 200 μm, and 300 μm below the surface, compared with the HV1 Vickers hardness (HV1 bulk) measured in bulk, is at least HV1% > 8.05 - 0.0035 × HV1 bulk.

[0008] This advantage is that the crushing strength of the excavation insert increases, which in turn leads to an extension of the life of the excavation insert.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] In one aspect of the present invention, there is provided a method for treating a sintered excavation insert containing cemented carbide, the method comprising subjecting the excavation insert to a surface hardening treatment, the surface hardening treatment being carried out at a high temperature of 100°C or higher, preferably at a temperature of 200°C or higher, more preferably at a temperature of 200°C to 450°C.

[0011] As used herein, "cemented carbide" means a material containing at least 50% by weight of WC, optionally other hard components common in the field of cemented carbide manufacturing technology, and preferably one or more selected from Fe, Co, and Ni as the metal binder phase. In one embodiment of the method, the cemented carbide excavation insert contains a hard phase containing at least 80% by weight of WC, preferably at least 90% by weight of WC.

[0012] The metal binder of the cemented carbide can contain other elements that dissolve in the metal binder during sintering, such as W and C derived from WC. Depending on the other types of hard components present, other elements can also dissolve in the binder.

[0013] Surface hardening treatment is defined as any treatment that introduces compressive stress into the material by physical impact and results in strain hardening on the surface and beneath it, such as tumbling or shot peening. The surface hardening treatment is performed after sintering and grinding. Unexpectedly, it has been found that the treatment of mining inserts using surface hardening treatment at high temperature reduces or even eliminates the impact damage between cemented carbides, such as chipping and micro-cracking, and thus improves the product life. The surface hardening treatment of the present invention is performed at a high temperature, which is defined herein as the temperature of the mining insert at the start of the surface hardening treatment. The upper limit of the temperature at which the surface hardening treatment is performed is preferably less than the sintering temperature, more preferably less than 900 °C. The temperature of the mining insert is measured by any suitable method suitable for measuring temperature, such as infrared temperature measurement.

[0014] In one embodiment of the present invention, the mining insert is subjected to surface hardening treatment at a temperature between 150 and 250 °C, preferably between 175 and 225 °C.

[0015] In one embodiment of the present invention, the upper limit of the surface hardening treatment is 700 °C, preferably 600 °C, more preferably 550 °C.

[0016] In one embodiment of the present invention, the mining insert is subjected to surface hardening treatment at a temperature between 300 and 600 °C, preferably between 350 and 550 °C, more preferably between 450 and 550 °C.

[0017] This temperature is measured on the mining insert using any suitable method for measuring temperature. Preferably, an infrared temperature measuring device is used.

[0018] In one embodiment, the cemented carbide contains a hard component in the metal binder phase, and the content of the metal binder phase in the cemented carbide is 4 to 30% by weight, preferably 5 to 15% by weight.

[0019] The content of the bonding phase needs to be high enough to result in the tough behavior of the mining insert. The content of the metal bonding phase is preferably 30 wt% or less, preferably 15 wt% or less. If the content of the bonding phase is too high, the hardness and wear resistance of the mining insert will decrease. The content of the metal bonding phase is preferably more than 4 wt%, more preferably more than 6 wt%.

[0020] In one embodiment, the metal bonding phase contains at least 80 wt% of one or more metal elements selected from Co, Ni, and Fe.

[0021] Preferably Co and / or Ni, most preferably Co, and even more preferably 3 to 20 wt% of Co. Optionally, the binder is a nickel-chromium or nickel-aluminum alloy. The cemented carbide mining insert may also optionally contain a crystal refinement compound in an amount of 20 wt% or less of the binder content. The crystal refinement compound is appropriately selected from the group of carbides, mixed carbides, carbonitrides, or nitrides of vanadium, chromium, tantalum, and niobium. The remainder of the cemented carbide mining insert is composed of one or more hard phase components.

[0022] In one embodiment, the cemented carbide further contains Cr in an amount such that the mass ratio of Cr / binder is 0.043 - 0.19.

[0023] The mass ratio of Cr / binder is calculated by dividing the weight percentage (wt%) of Cr added to the powder blend by the wt% of the binder in the powder blend, and this weight percentage is based on the weight of that component compared to the total weight of the powder blend. Cr dissolves to a considerable extent in the bonding phase, but some amount, for example up to 3 mass% of undissolved chromium carbide, may be present in the cemented carbide body. However, it may be preferred not to add Cr beyond the mass ratio of Cr / binder such that all of the Cr dissolves in the binder so that the sintered cemented carbide body does not contain undissolved chromium carbide.

[0024] The mass ratio of Cr / binder can be 0.043 - 0.19, preferably 0.075 - 0.15, more preferably 0.085 - 0.12. If the mass ratio of Cr / binder is too low, the positive effect of Cr becomes too small. On the other hand, if the mass ratio of Cr / binder is too high, the formation of the chromium carbide concentration at which the binder dissolves increases, thereby reducing the volume of the binder phase, and as a result, the cemented carbide body becomes too brittle.

[0025] Cr is usually added to the powder blend in the form of Cr 3 C 2 because this has the highest proportion of Cr per gram of powder, but Cr 26 C 2 or Cr 7 C 3 It should be understood that Cr can be added to the powder blend using alternative chromium carbides such as Cr

[0026] The addition of Cr also has the effect of improving the corrosion resistance of the cemented carbide. The presence of Cr also makes it easier to deform the binder from fcc to hcp during excavation, which is beneficial for absorbing part of the energy generated during the excavation process. Thereby, this deformation hardens the binder phase and reduces its wear during button use. The presence of Cr enhances the wear resistance of the cemented carbide and its strain hardening ability. By mixing Cr into the cemented carbide powder and applying a powder containing a crystal refinement compound and optionally a carbon-based grain growth promoter to at least a part of the surface of the compact, a cemented carbide body having a chemical gradient and a hardness gradient that generates a cemented carbide mining insert having high wear resistance is produced.

[0027] Apart from the solid-phase forming component, the binder, and the Cr-containing component, incidental impurities may be present in the WC-based starting material.

[0028] In one embodiment of the present invention, the cemented carbide before being subjected to the surface hardening treatment has a bulk hardness between 1200 - 1900 HV1, preferably 1300 - 1850 HV1, and most preferably 1400 - 1700 HV1.

[0029] In one embodiment of the present invention, the cemented carbide is not coated.

[0030] In one embodiment of the present invention, the cemented carbide is M 7 C 3 carbide, and optionally M 3 C 2 carbide is also included, where M is Cr and optionally one or more of W, Co, and any other elements added to the cemented carbide. This means that in the SEM (scanning electron microscope) image using backscattering at a magnification sufficient to detect particles of 100 nm size, M 7 C 3 carbide should be clearly visible. In one embodiment of the present invention, the cemented carbide contains M 7 C 3 carbide in an amount given by the ratio of volume % of M 7 C 3 carbide to volume % of Co. Appropriately, the ratio of volume % of M 7 C 3 carbide to volume % of Co is between 0.01 and 0.5, preferably between 0.03 and 0.25. The volume % of M 7 C3 carbide and Co binder can be measured by EBSD or image analysis using appropriate software.

[0031] In one embodiment, the cemented carbide has a Com / Co ratio of 0.75 ≦ Com / Co ≦ 0.98. Com is the magnetic saturation in weight %, and "Co" is the weight percentage of cobalt in the cemented carbide. Com is related to the magnetic saturation 4πσ 0 = 201.9 [μTm 3 / kg] of pure metallic Co binder by the following equation for the magnetic saturation 4πσ 1 [μTm 3 / kg] of the cemented carbide. Com(%) = 4πσ 1 * (100 / 201.9)

[0032] References: "Measurement Good Practice Guide No.20" by Roebuck et al., 1999, non-patent document

[0033] In one embodiment, the cemented carbide does not contain an eta phase and graphite. When the binder phase consists of cobalt, the cemented carbide does not contain an eta phase and graphite when the Com / Co ratio is 0.75 ≦ Com / Co ≦ 0.98. Metals used as binder phases in cemented carbides such as Co, Ni, and Fe are ferromagnetic. The saturation magnetization is the maximum possible magnetization of a ferromagnetic material and is characterized by the parallel alignment of all magnetic moments inside the material. The magnetic saturation (Com) dipole moment jS and the derived weight ratio saturation magnetization σS (4πσ) of the insert are determined using a Foerster KOERZIMAT 1.096. Then, the Co content is measured by XRF (X-ray fluorescence) using a Malvern Panalytical Axios Max Advanced instrument. The range of Com / Co% between eta phase and graphite formation is affected, for example, by changing the composition of the binder by adding Cr, Fe, Ni, etc.

[0034] The solubility of W in the binder phase is directly related to the carbon content. The amount of W in the binder increases as the carbon content decreases until the limit of eta phase formation is reached. When the carbon content further decreases, the solubility of W in the binder no longer increases. In some cemented carbide grades where it is beneficial to obtain a large amount of W dissolved in the binder, the carbon content is kept low but exceeds the limit of eta phase formation.

[0035] In another embodiment of the present invention, the cemented carbide substrate is Me 12 C carbide and / or Me 6It contains an eta phase containing C carbide, where Me is one or more metals selected from W, Mo, and binder-phase metals. The cemented carbide has a Com / Co ratio ≤ 0.69. When other components, such as grain growth inhibitors, gamma-phase formers, etc., are added to the cemented carbide, the Com / Co ratio is affected. However, the formed eta phase does not exist as large aggregates. Generally, the eta phase has conventionally been considered undesirable in cemented carbides because it is brittle and exists in large aggregates of eta-phase particles that are harmful to the properties of the cemented carbide. The cemented carbide according to this embodiment of the present invention should have a uniformly distributed eta phase, which, in this specification, means that the cemented carbide does not contain large aggregates. The amount of the eta phase is at least 2% by volume, preferably at least 4% by volume. By selecting a certain range of stoichiometric carbon contents to form a non-aggregated eta phase, like the cemented carbide of this embodiment, the cemented carbide exhibits good properties. The eta phase exists as a finely dispersed phase in the microstructure. The general carbide of the eta phase is W 6 Co 6 C, W 3 Co 3 C, W 6 Ni 6 C, W 3 Ni 3 C, W 6 Fe 6 C, W 3 Fe 3 is C. In one embodiment, the eta phase contains both Me 12 C and Me 6 C.

[0036] In one embodiment, the method further includes applying a grain growth promoter, which is carbon, to at least a part of the surface of the compact of the cemented carbide before sintering a liquid dispersion or slurry containing a grain refiner and carbon and / or nitrogen, and both the grain refinement compound and the grain growth promoter are provided on one or more surfaces in an amount of 0.1 - 100 mg / cm 2 of.

[0037] The crystal refinement compound is a carbide, mixed carbide, carbonitride or nitride, and the crystal refinement compound and the grain growth accelerator are provided on the surface of the compact by first preparing the compact and then applying the crystal refinement compound and the grain growth accelerator to at least a part of the surface of the compact. The crystal refinement compound and the grain growth accelerator are provided by applying them to the compact in the form of a separate or combined liquid dispersion or slurry, and the weight ratio of the crystal refinement compound to the grain growth accelerator is from about 0.05 to about 50. Before the surface hardening treatment, after applying the crystal refinement compound and the grain growth accelerator to the surface of the compact, the compact is sintered.

[0038] The crystal refinement compound is preferably a carbide or nitride of chromium or vanadium. Further details of the method of applying the crystal refinement compound and the grain growth accelerator to the surface of the cemented carbide can be found in European Patent No. 2355948.

[0039] In one embodiment, the method includes a step of heating the mining insert and the medium before the surface hardening treatment, and the surface hardening treatment is performed on the heated mining insert.

[0040] The mining insert can be heated in a separate step before the surface hardening treatment step. Several methods can be used to create the high temperature of the mining insert, such as using induction heating, resistance heating, hot air heating, flame heating, preheating on a high-temperature surface in an oven or furnace, or laser heating.

[0041] In an alternative embodiment, the mining insert is maintained in a heated state during the surface hardening treatment. For example, an induction coil is used.

[0042] In one embodiment, after subjecting the mining insert to a surface hardening treatment at a high temperature, the mining insert is subjected to a second surface hardening treatment at room temperature. Advantageously, this removes debris and oxides, such as iron oxide, deposited on the insert surface from the inside of the processing container. The second surface hardening treatment carried out at room temperature can be carried out in a wet state and helps to remove dust and dirt from the mining insert being processed, reducing health hazards.

[0043] In one embodiment, the surface hardening treatment is tumbling. The tumbling treatment can be centrifugal or vibratory. A "standard" tumbling treatment is typically carried out using a vibratory tumbler, such as a Reni Cirillo RC 650, in which case about 30 kg of inserts are tumbled at about 50 Hz for about 40 minutes. An alternative typical "standard" tumbling treatment is to use a centrifugal tumbler, such as an ERBA-120 with a closed lid at the top and a rotating disk at the bottom. Another method is centrifugal barrel finishing. In both centrifugal treatments, the rotation causes the inserts to collide with other inserts or any additional media added. In "standard" tumbling using a centrifugal tumbler, the tumbling step is typically carried out at 120 RPM for at least 20 minutes. The lining of the tumbler can form oxides or metal deposits on the surface of the inserts.

[0044] It may be necessary to modify the lining of the tumbler so that it can withstand the higher temperatures at which the treatment is carried out.

[0045] In one embodiment, the tumbling treatment is a "high energy tumbling" (HET) treatment, where after tumbling, a homogeneous cemented carbide mining insert is strain hardened to * HV3 バルク ΔHV3%≧9.72 - 0.00543 HV3, where ΔHV3% is the percentage difference between the HV3 measurement at 0.3 mm from the surface and the HV3 measurement in the bulk, compared to the HV3 measurement in the bulk.

[0046] To introduce a high level of compressive stress into the cemented carbide mining insert, high energy tumbling (HET) treatment can be used. There are many different possible processing setting conditions that can be used to introduce HET, including the type of tumbler, the amount of media added (if any), the processing time, and the processing setting conditions, such as the RPM of a centrifugal tumbler. Therefore, it is most appropriate to define HET from the perspective of "any processing setting conditions that introduce a certain degree of strain hardening into a homogeneous cemented carbide mining insert having a mass of about 20 g". In the present disclosure, HET is defined as a tumbling process that introduces a hardness change of at least (ΔHV3%) measured using HV3 after tumbling. ΔHV3% = 9.72 - 0.00543 * HV3 バルク (Equation 1)

[0047] [wherein, ΔHV3% = 100 * (HV3 0.3mm - HV3 バルク ) / HV3 バルク (Equation 2) HV3 バルク is the average of at least 30 indentation points measured at the deepest part (center) of the cemented carbide mining insert, and HV3 0.3mm is the average of at least 30 indentation points 0.3 mm below the tumbling surface of the cemented carbide mining insert] This is based on measurements performed on a cemented carbide mining insert having homogeneous properties. "Homogeneous properties" means that the hardness difference from the surface zone to the bulk zone is 1% or less after sintering. The tumbling parameters used to achieve the strain hardening described in Equations (1) and (2) on a homogeneous cemented carbide mining insert are applied to a cemented carbide body having gradient properties.

[0048] HET tumbling may typically be performed using an ERBA120 having a disk size of about 600 mm. When performing the tumbling process without using a medium or using a medium larger in size than the insert to be tumbled, it may be performed at about 150 RPM. Alternatively, when the medium to be used is smaller in size than the insert to be tumbled, it may be performed at about 200 RPM. Also, when using a Roesler tumbler having a disk size of about 350 mm, when performing the tumbling process without using a medium or using a medium larger in size than the insert to be tumbled, it may be performed at about 200 RPM. Alternatively, when the medium to be used is smaller in size than the insert to be tumbled, it may be performed at about 280 RPM. Typically, the parts are tumbled for at least 40 - 60 minutes.

[0049] In one embodiment, the tumbling process is performed under dry conditions. The effect of the surface hardening treatment at high temperature is enhanced when the treatment is performed under dry conditions. "Dry" conditions mean that no liquid is added to the treatment. Without being bound by this theory, it is believed that when a liquid is introduced into the treatment, the temperature of the parts is reduced. Further, by including a liquid, the degree of impact between the tumbling parts is reduced. Internal friction generates heat and does not allow it to be lost.

[0050] The tumbling process can be performed in the presence or absence of a tumbling medium, depending on the shape and material composition of the mining insert to be tumbled. If it is determined to add a tumbling medium, the type and ratio of the medium to the insert are selected to be compatible with the shape and material composition of the mining insert to be tumbled.

[0051] In some cases, all or part of the heat is generated by the friction between the insert and any medium added in the tumbling process.

[0052] Optionally, the insert is further subjected to a second surface hardening treatment. Preferably, when the second surface hardening treatment is carried out at room temperature, this second surface hardening treatment is HET tumbling at room temperature in a wet state.

[0053] In one embodiment, the mining insert treated by surface hardening treatment at high temperature has an increase in the HV1 Vickers hardness measurement value (HV1%) from the surface region, measured as the average of HV1 at a depth of 100 to 300 μm below the surface, compared to the HV1 Vickers hardness measured in bulk (HV1 bulk), of at least HV1% > 8.05 - 0.00350 × HV1 bulk, preferably HV1% > 8.45 - 0.00355 × HV1 bulk. Preferably, HV1% < 17.5 - 0.00662 × HV1 bulk. This is shown in Figure 2.

[0054] The term "bulk" means the deepest part (center) of the cutting tool in this specification and is the region with the lowest hardness in the present disclosure.

[0055] The hardness of the cemented carbide insert is measured using automatic Vickers hardness measurement. The cemented carbide body is cut along the vertical axis and polished using standard procedures. The cutting is carried out using a diamond disk cutter under running water. Then, Vickers indentations with a 1 kg load are assigned equidistantly across the polished cross-section at a given depth below the surface. The hardness of the surface region is the average of approximately 180 indentations obtained at distances of 100, 200, and 300 μm below the surface. The hardness of the bulk is the average of approximately 150 indentations obtained at distances of 4.50, 4.65, and 4.80 mm below the surface. Figure 1 shows the layout of HV1, and the filled squares represent the positions of the surface indication 2 and the bulk indication 4.

[0056] The hardness measurement is carried out using a programmable hardness tester KB30S by KB Pruftechnik GmbH, calibrated against an HV1 test block issued by Euro Products Calibration Laboratory (UK). The hardness is measured in accordance with ISO EN6507.

[0057] The HV1 measurement was performed by the following method. - Scan the edge of the sample. - Program the hardness tester to make an indentation at a specified distance from the edge of the sample. - Make an indentation with a load of 1 kg at all the programmed coordinates. - The computer moves the stage to each coordinate, places the microscope over each indentation, activates the auto light and auto focus, and automatically measures the size of each indentation. - The user examines all the photos of the indentations for problems such as out-of-focus or other issues that would interfere with the results.

[0058] In one embodiment, the residual stress of a 20 g mining insert after surface hardening treatment at high temperature is at least 1250 MPa.

[0059] The residual stress measurement values were analyzed using X-ray diffraction on the upper part of the insert by using a Bruker D8 Discovery equipped with Cu Kα (1.54 Å) with a parallel beam polycapillary and a collimator with an aperture of 0.5 mm.

[0060] This measurement was performed at 11 ψ angles from -45° to 45° and 3 φ angles of 0°, 45°, and 90° using the equal inclination method (sin2ψ method). The elongation was calculated for the peak displacement of the Bragg peak of hkl:311 (117.32° 2θ). The software Leptos (Bruker) was used for the calculation of the residual stress. The input values for the calculation were 650 MPa for the E modulus and 0.19 for the Poisson's constant. Assuming no direction dependence for the residual stress, the "normal" voltage model (not biaxial) was used. And the measured values at the 3 φ angles for each sample were regarded as individual measured values. The diffractometer is constantly checked with a collander sample (NIST standard) to ensure alignment.

Example

[0061] Example 1 - Starting Materials and Tumbling Conditions Mining inserts with various compositions (based on the starting composition of the powders weighed into the comminution) were tested. Table 1 shows an overview of the compositions of the mining inserts tested. TIFF0007690478000001.tif55170Table 1: Compositions of the mining inserts tested. * Since D is the gradient, it was measured 0.5 mm below the tip.

[0062] Samples A, E, and F represent the "standard" cemented carbide grades used for mining inserts. Samples B and G contain chromium, and sample C contains an eta phase. All cemented carbide inserts were manufactured using WC powder with a particle size measured by FSSS between 5 and 18 μm before comminution. The WC powder and Co powder were milled under wet conditions using ethanol in a ball mill with the addition of 2 wt% polyethylene glycol (PEG8000), an organic binder (pressing agent), and the cemented carbide comminution. After milling, this mixture was spray-dried in an N 2 atmosphere and then uniaxially pressed into mining inserts having a size of approximately 10 mm in outer diameter (OD) and approximately 17 - 20 mm in height, having a weight of approximately 20 g, each having a spherical dome ("cutting edge") at the top. Then, this sample was sintered using Sinter-HIP at 1410 °C for 1 hour at an Ar pressure of 55 bar. Sample D is the same starting material as sample A, but before sintering, the sample was immersed in a slurry containing 25 wt% Cr 3 C 2 and 5 wt% graphite so that approximately 60% of the total length of the insert was exposed to the slurry and coated on the surface of the cemented carbide mining insert.

[0063] For comparison, each batch of 25 or 50 of samples A - D was treated using HET centrifugal tumbling treatment at 25 °C (room temperature) for 50 minutes at 300 RPM in a Roesler FKS04 tumbler under wet conditions with 50 kg of 7 mm carbide balls of grade H10F. In the result table, samples treated according to this method are referred to as "25 °C wet HET".

[0064] To reproduce tumbling at high temperatures at the laboratory scale, the "high-temperature shaking" method has been used. The high-temperature shaking method uses a commercially available paint shaker of the trademark Corob (TM) Simple Shake 90 with a maximum load of 40 kg and a maximum shaking frequency of 65 Hz. The "high-temperature shaking" method was carried out at a frequency of 45 Hz in batches of 50 mining inserts. Approximately 800 grams or 50 inserts and 4.2 kg of carbide media (1560 balls of approximately 7 mm) were placed in a cylindrical steel container with an inner diameter of 10 cm and an internal height of 12 cm and filled to 2 / 3 of the height. The steel cylinder equipped with the mining inserts was heated together with the media in the furnace to a high temperature of 100 °C, 200 °C or 300 °C, and the mining inserts were held at the target temperature for 120 minutes. After heating, the steel cylinder was quickly transferred to the paint shaker and shaken immediately for 9 minutes. The transfer time between the furnaces until the shaker started was less than 20 seconds. The media was made of cemented carbide grade H10F with 10 wt% Co, 0.5 wt% Cr and 89.5 wt% WC, which results in approximately 1600 sintered HV20. Samples processed according to this method are referred to in the result table as "100 °C dry shaking", "200 °C dry shaking" or "300 °C dry shaking" depending on the temperature used. The shaking was carried out under dry conditions, in other words, no water was added to the shaking. Some samples were also processed by shaking under dry conditions at room temperature, and in the result table, this method is referred to as "25 °C dry shaking". For these samples, 25 °C indicates the temperature at the start of the treatment, but due to the frictional heat and impact heat generated during the 9-minute shaking treatment, the final temperature inside the steel cylinder is actually 60 - 100 °C, that is, it "rises". After shaking, the samples were then cooled and processed using the above-mentioned HET centrifugal tumbling treatment and a second surface hardening treatment. In the result table, the samples processed according to this method are referred to as "300 °C shaking dry + 25 °C HET wet".

[0065] Example 2 - Edge Damage To obtain the highest yield, it is important that there is little or preferably no damage to the edges of the mining inserts after tumbling.

[0066] To compare the yields of good-quality mining inserts when the surface hardening treatment was carried out at room temperature to 300 °C, the mining inserts were visually inspected for damage after tumbling. A mining insert was counted as having damage when the chipping exceeded about 1 mm in length or when the chipping reached the cylindrical surface of the insert's coreless ground. The percentage of damaged inserts was reported in Table 2. TIFF0007690478000002.tif49170Table 2: Percentage of mining inserts damaged after tumbling treatment

[0067] The temperature for the described surface hardening treatment is the starting temperature. In the batch treated at a starting temperature of 25 °C, when water was added to the treatment, it was not expected that the temperature would rise significantly when the sample was being treated. In the samples treated under dry conditions, heat was generated due to the friction between the insert and the medium in the tumbling process, so the temperature increased. The results in Table 2 show that when the surface hardening treatment is carried out at a high temperature, the amount of edge damage to the mining insert decreases.

[0068] Example 3 - Insert Compression Test The insert compression test method involves compressing a drill bit insert between two flat parallel hard opposing surfaces at a constant displacement rate until the insert breaks. A test fixture based on the ISO 4506:2017(E) standard "Hardmetals - Compression test" was used together with a cemented carbide anvil with a hardness exceeding 2000 HV, while the test method itself was adapted to the toughness test of the rock drilling insert. The fixture was attached to an Instron 5989 test frame.

[0069] The load axis was identical to the axis of rotational symmetry of the insert. The opposing surfaces of the fixture met the parallelism required by ISO 4506:2017(E), i.e., a maximum deviation of 0.5 μm / mm. A constant crosshead displacement speed equal to 0.6 mm / min was applied to the tested inserts while recording the load-displacement curve until failure. Before the evaluation of the test, the compliance of the test apparatus and the test fixture was subtracted from the measured load-displacement curve. Five inserts were tested for each sample type. Before each test, the damage to the opposing surfaces was inspected. The failure of the insert was defined as occurring when the measured load suddenly decreased by at least 1000 N. Subsequent inspection of the tested inserts confirmed that this corresponded to the occurrence of cracks visible to the naked eye in all cases. Material toughness was characterized by the total absorbed deformation energy up to failure. An overview of the fracture energy in joules (J) required to fracture the samples is shown in Table 3 below. TIFF0007690478000003.tif65170Table 3: Fracture energy (J) required to fracture the samples (Grade E was tested with a tip radius of 2.5 mm and all other grades were tested with a tip radius of 5 mm.)

[0070] It can be seen that when the surface hardening treatment is carried out at a high temperature, the fracture energy increases in all samples compared to when it is carried out at room temperature.

[0071] Example 4 - Field Test A top hammer bit having an initial bit diameter of approximately 49 mm and six peripheral inserts with a diameter of 10 mm and three front inserts with a diameter of 9 mm was fabricated. The insert shape was conical with a spherical top having a radius of 2.5 mm.

[0072] Two bits were tested using each of the following types of inserts. Sample A, treated according to the standard centrifugation method "25°C wet HET" surface hardening treatment, which represents a standard insert used for top hammer drilling. Sample E, treated according to the "25°C wet HET" surface hardening treatment, this material is generally considered too brittle and not suitable for top hammer drilling. Sample E, treated according to the "300°C dry vibration + 25°C wet HET" surface hardening treatment, which is a sample of the present invention. These bits were tested on granite rock at the Sandvik test mine in Myllypuro, Finland. The drill rig was equipped with an HLX5 rock drill and operated at full power meaning an impact pressure of 200 bar, a feed pressure of 100 bar, a rotation of 240 RPM and a rotary pressure of 120 bar. If the bit cracked or if bit regrinding was required before drilling could continue, the bit was classified as damaged. The average results obtained from the two bits (per case) are shown in Table 4 below. TIFF0007690478000004.tif52170Table 4: Results of field tests

[0073] By subjecting the surface hardening treatment at high temperature, it can be seen that the drilling performance of the sample of the present invention is improved compared to the standard material used for top hammer drilling (Sample A heated according to the conventional method "25°C wet HET"), and it can be seen that the drilling performance is improved even for insert grade E which usually exhibits very poor performance when the surface hardening treatment is carried out only at room temperature.

[0074] Example 5 - Hardness Measurement Hardness measurements were made for the samples described in Table 1 according to the description previously explained herein. The HV1 hardness was measured at the bulk (the value in Table 1) and at depths of 100, 200 and 300 μm below the surface of the longitudinal section sample, and the ratio of the hardness increase compared to the bulk is reported in Table 5 for the samples treated according to the "300°C dry vibration + 25°C wet HET" surface hardening method. TIFF0007690478000005.tif39170Table 5: Rate of increase of HV1 at different depths below the surface compared to the bulk

[0075] In all cases, it can be seen that there is an increase in HV1 on the surface of the mining insert compared to the bulk.

[0076] Example 6 - Measurement of Residual Stress Residual stress measurements were performed on the above samples according to the method described earlier in this specification. Table 6 shows that the residual stress in the samples is higher after tumbling post-treatment at high temperature compared to tumbling post-treatment at room temperature. TIFF0007690478000006.tif49170 Table 6: Compressive stress measurement values (Mpa)

Claims

Claim 1 A method for treating a sintered mining insert containing cemented carbide, comprising: The cemented carbide contains a hard component in a metal binder phase, and the content of the metal binder phase in the cemented carbide is 4 to 30% by weight; The metal binder phase contains at least 80% by weight of one or more metal elements selected from Co, Ni, and Fe; The hard phase contains a hard phase containing at least 80% by weight of WC; the mining insert is subjected to a surface hardening treatment, The surface hardening treatment is tumbling; The tumbling treatment is performed under dry conditions; The tumbling treatment is a "high energy tumbling" treatment, and after tumbling, a homogeneous cemented carbide mining insert is strain hardened so that ΔHV3% ≥ 9.72 - 0.00543 * HV3 bulk (where ΔHV3% is the percentage of the difference between the HV3 measurement value at 0.3 mm from the surface and the HV3 measurement value in the bulk compared to the HV3 measurement value in the bulk). A method characterized in that the surface hardening treatment is carried out at a high temperature of 100°C or higher. Claim 2. The method according to claim 1, characterized in that the surface hardening treatment is carried out at a temperature of 200°C or higher. Claim 3. The method according to claim 1, characterized in that the surface hardening treatment is carried out at a temperature between 200°C and 450°C. Claim 4. The method according to any one of claims 1 to 3, wherein the content of the metal binder phase in the cemented carbide is 5 to 15% by weight. Claim 5 The method according to any one of claims 1 to 4, wherein the cemented carbide further contains Cr in an amount such that the mass ratio of Cr / binder is 0.043 - 0.

19. Claim 6 The cemented carbide contains M ７ C ３ The method according to any one of claims 1 to 5, wherein the carbide is included. Claim 7 The method according to any one of claims 1 to 6, comprising a step of heating the mining insert and the medium before the surface hardening treatment, and the surface hardening treatment is performed on the heated mining insert. Claim 8 The method according to any one of claims 1 to 7, wherein after the mining insert is subjected to a surface hardening treatment at a high temperature, the mining insert is subjected to a second surface hardening treatment at room temperature.

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