Rock Drill Inserts

Abstract

1. A rock drill insert comprising a cemented carbide body containing a hard constituent of WC in a binder phase comprising cobalt, the cemented carbide containing 4-18 wt. % Co and Cr such that the Cr / Co mass ratio in the bulk of the body is 0.04-0.19, with the balance being WC and unavoidable impurities, the binder phase content of the cemented carbide being substantially equal throughout the rock drill insert, the insert having a modified CoM / Co wt. % ratio between 0.70 and 0.81, the insert being substantially free of eta phase, the modified CoM / Co wt. % ratio being calculated according to: Modified CoM / Co wt. % = (CoM / Co wt. % + 1.13 x Cr wt. %) / Co wt. %, where CoM / Co wt. % is the weight percentage of magnetic Co, and Co wt. % and Cr wt. % are the weight percentages of Co and Cr in the cemented carbide, respectively.

Description

[Technical Field]

[0001] The present invention relates to rock drill inserts containing chromium alloyed cemented carbide having a specially selected narrowly limited range of modified CoM / Co weight percentages. [Background technology]

[0002] Rock drilling is a technical field in which inserts used to drill into rock are subjected to high stresses, repeated impacts, and severe corrosive conditions due to the inherent nature of drilling. Different drilling techniques result in different loads on the inserts, which are caused by a combination of contact stresses, impacts, shear, and bending. Particularly severe stress conditions are found in applications where rock drill inserts are mounted in rock drill bit bodies of tophammer (TH) or down-the-hole (DTH) drilling equipment, or rotary drilling, raise-boring, or mechanical cutting equipment.

[0003] Conventionally, rock drill inserts may be constructed with a cemented carbide body containing a hard component (e.g., tungsten carbide (WC)) in a binder phase (e.g., cobalt (Co)). It is desirable to improve the insert's lifespan. International Publication No. 2018 / 060125 (WO2018 / 060125) discloses the addition of chromium to cemented carbide to enhance drill bit performance. However, there is a need for further improvements in insert performance and lifespan, particularly in hard rock drilling applications. European Patent Application Publication No. 3763840 (EP3763840) discloses cemented carbide mining inserts with a gradient microstructure, and European Patent Application Publication No. 2011890 (EP2011890) discloses cemented carbide compositions having a Cr / Co ratio of 0.05 to 0.15 by weight.

[0004] The problem to be solved is therefore how to further improve the life of the drill insert.

[0005] definition As used herein, the term "bulk" refers to the innermost (center) cemented carbide portion of the rock drill insert. This is considered to be the volume of the insert excluding the outer 2 mm from the surface (i.e., everything excluding the surface and subsurface).

[0006] As used herein, "eta phase" refers to M6C or M 12 C, where M=(Co, W, Cr).

[0007] Summary of the Invention An object of the present invention is to improve the service life of cemented carbide inserts, which object is achieved by providing a rock drill insert which: 1. A rock drill insert comprising a cemented carbide body containing a hard component of tungsten carbide (WC) in a binder phase containing cobalt, The cemented carbide contains 4 to 18 wt% Co, Cr such that the Cr / Co mass ratio in the bulk of the body is 0.04 to 0.19, and the remainder is WC and inevitable impurities, The binder phase content of the cemented carbide is substantially equal throughout the rock drill insert; the insert has a modified CoM / Co wt% ratio between 0.70 and 0.81, the insert being substantially free of eta phase; The modified CoM / Co wt% ratio is calculated using Equation 1: Modified CoM / Co weight%=(Co magnetism%+1.13×Cr weight%) / Co weight% Equation 1 where Co magnetic % is the weight percentage of magnetic Co, and Co wt % and Cr wt % are the weight percentages of Co and Cr in the cemented carbide, respectively.

[0008] Surprisingly, it has been found that when inserts having this particular range of modified CoM / Co wt% are subjected to static / low strain rate contact stresses (which may be due to mechanical post-sintering processes, such as high-energy tumbling, and / or the actual drilling process), the strain-hardening ability of the material is advantageously enhanced. The material also exhibits enhanced ultimate compressive strength (UCS), leading to a reduced risk of premature insert failure in rock drilling applications. This is surprising, since a person skilled in the art would typically consider using a cemented carbide with a higher CoM / Co wt% to avoid embrittlement. Furthermore, it has been found that when the modified CoM / Co wt% is within this range, the wear characteristics of the insert are improved, contributing to an increased insert life in field use.

[0009] In one embodiment, the cobalt content is 8-18 wt. Advantageously, this range facilitates achieving high fracture toughness in the material, making it particularly suitable for toughness-focused rock drilling applications (e.g., rotary drill bits, raise-boring pilot bits, and raise-boring cutters). A further advantage of this cobalt range is that the claimed Cr / Co mass ratio, combined with the modified CoM / Co wt. % ratio, enhances the material's plasticity in compression. The term "plasticity" is used herein to refer to a material's ability to undergo higher plastic strains before the onset of failure. Typically, in material design, increasing its ultimate strength decreases its plasticity, and vice versa. In the present invention, this cobalt range simultaneously enhances the material's ability to strain-harden in compression, its USC, and its plasticity, leading to a reduced risk of premature insert failure in rock drilling applications. Furthermore, the enhanced plasticity and strain hardening during compression can optimally increase the level of residual stresses induced within the material, further improving the insert's resistance to premature failure and thus extending the insert's lifespan.

[0010] In another embodiment, the cobalt content is between 4 and 8 wt. %. This range advantageously makes it possible to reach particularly high wear resistance, which is typically required in applications such as tophammer drilling and down-the-hole drilling.

[0011] In one embodiment, the modified CoM / Co wt% is between 0.73 and 0.79, which advantageously, in combination with a cobalt content between 8 and 18 wt%, optimally enhances the strain hardening ability and plasticity of the material in compression.

[0012] In one embodiment, the difference between the average hardness of the rock drill insert 0.3 mm below the surface and the average hardness in the bulk of the rock drill insert is at least 30 HV3, as measured by hardness according to EN ISO 6507-1:2005 (E). The hardness difference arises from mechanically induced compressive residual stresses and strain hardening of the binder phase. Advantageously, this increases the strength and apparent toughness of the rock drill insert, reducing the risk of premature damage and fracture of the insert and consequently extending the life of the insert.

[0013] In one embodiment, the difference in hardness between any point 0.3 mm below the surface of the rock drill insert and the hardness at 1 mm below the surface of the rock drill insert is at least 20 HV3, as measured by hardness according to EN ISO 6507-1:2005 (E). This hardness difference reflects compressive residual stresses and strain hardening induced in the binder phase, which improves the apparent toughness and strength of the insert and, consequently, its life during drilling.

[0014] In one embodiment, the cemented carbide has an average WC grain size greater than 0.7 μm but less than 18 μm, as measured according to the Jeffries method defined herein below, which advantageously provides an optimum balance of wear resistance and toughness for rock tool applications.

[0015] In one embodiment, the cemented carbide has an average WC grain size of at least 1.0 μm but less than 10 μm, which advantageously provides an optimum balance of wear resistance and toughness for rock tool applications.

[0016] In one embodiment, the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.17, preferably between 0.065 and 0.16, and more preferably between 0.075 and 0.15, which advantageously provides optimal wear resistance and strain hardening capacity.

[0017] In another embodiment, the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.12, which advantageously provides an optimum balance between plasticity, strain hardening ability, wear resistance and fracture toughness.

[0018] In one embodiment, the cemented carbide has a bulk hardness of 1750 HV20 or less, which advantageously means that the insert is not so brittle that it is prone to breakage.

[0019] According to another aspect of the present application, there is a rock drill bit body having attached thereto one or more rock drill inserts as described above or below. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows a schematic representation of the geometry of the rock drill inserts used in the wear tests. [Figure 2] The deformation curves of samples A and B under uniaxial compression are shown. [Figure 3] The deformation curves of samples C and D under uniaxial compression are shown. [Figure 4] The deformation curves of samples E and F under uniaxial compression are shown.

[0021] Detailed Description FIG. 1 shows a rock drill insert 2 comprising a body of cemented carbide containing the hard constituent WC in a binder phase containing cobalt, said rock drill insert 2 comprising: The cemented carbide contains 4 to 18 wt% Co, Cr such that the Cr / Co mass ratio in the bulk of the body is 0.04 to 0.19, and the remainder is WC and inevitable impurities, The binder phase content of the cemented carbide is substantially equal throughout the rock drill insert; the insert has a modified CoM / Co wt% ratio between 0.70 and 0.81, the insert being substantially free of eta phase; The modified CoM / Co wt% ratio is calculated using Equation 1: Modified CoM / Co weight%=(Co magnetism%+1.13×Cr weight%) / Co weight% Equation 1 where Co magnetic % is the weight percentage of magnetic Co, and Co wt % and Cr wt % are the weight percentages of Co and Cr in the cemented carbide, respectively.

[0022] This specific range of modified CoM / Co wt% is achieved by carefully controlling the carbon content. The modified CoM / Co wt% for the sintered samples is measured and calculated using a commercially available Foerster Koerzimat CS 1.096 instrument. The sample is weighed and then placed in a magnetic coil as described in the Koerzimat CS 1.096 V3.09 manual. The magnetic moment is measured, from which the weight-specific saturation magnetization, σs, is calculated as the ratio of the magnetic moment to the weight of the sample. The percentage of magnetic material (known as Co magnetic%) is then multiplied by σs, which is the material constant for Co (2010 10 -7 Tm 3 / kg). For chromium-containing materials, a correction factor of 1.13 x Cr wt% is used (the 1.13 factor is derived from the ratio of the atomic weights of cobalt and chromium), as per Equation 1 below: Modified CoM / Co weight%=(Co magnetism%+1.13×Cr weight%) / Co weight% Equation 1 where CoMag% is the weight percent of magnetic Co, and CoWt% and CrWt% are the weight percent of Co and Cr in the cemented carbide, respectively.

[0023] The desired modified CoM / Co weight percent is achieved by taking a sample of the powder blend slurry from the mill, then drying, pressing, and sintering it, allowing the modified CoM / Co weight percent to be measured and calculated. Using methods known to those skilled in the art, one can calculate the amount of carbon (soot) or very fine tungsten metal powder to be added to achieve the desired modified CoM / Co weight percent. This is essentially a means of controlling the carbon balance. However, because the absolute carbon content is affected by other factors (e.g., binder content, Cr content, and sintering conditions), it is necessary to use the methods described above to define the desired properties rather than measuring and controlling the absolute carbon content. The rock drill insert 2 of the present invention is manufactured by a process in which a ready-to-press powder containing cemented carbide elements is milled, spray-dried, and then consolidated into a compact, which is then sintered. A grinding step is typically performed to obtain the precise dimensions of the drill insert. The drill insert of the present invention generally has a cylindrical base portion and a rounded top portion, which may be hemispherical, conical, or asymmetrical. It should be understood that the rock drill insert may have alternative geometries than that shown in FIG. 1. The curved surface of the cylindrical base portion is typically ground to the desired precision diameter, while the surface of the top portion and the circular base portion remain in the sintered state. The drill insert then undergoes a mechanical post-processing step, which introduces high levels of compressive stress (e.g., high-energy tumbling) into the insert.

[0024] The binder phase content of the cemented carbide is substantially equal throughout the rock drill insert, i.e., there is substantially no gradient in Co content when going from the surface to the interior of the rock drill insert. Preferably, there is also substantially no gradient in Cr content when going from the surface to the interior of the rock drill insert.

[0025] In one embodiment, the cobalt content is preferably 5 to 16% by weight.

[0026] In another embodiment, the cobalt content is between 8 and 18% by weight, preferably between 10 and 16% by weight.

[0027] In another embodiment, the cobalt content is 4 to 10 wt. %, preferably 4 to 8 wt.

[0028] In one embodiment, the modified CoM / Co wt % is between 0.70 and 0.81, preferably between 0.72 and 0.80, more preferably between 0.73 and 0.79.

[0029] In one embodiment, the difference between the average hardness 0.3 mm below the surface of the rock drill insert and the average hardness in the bulk of the rock drill insert is at least 30 HV3, preferably at least 35 HV3, more preferably at least 40 HV3, even more preferably at least 40 HV3, even more preferably at least 50 HV3, and even more preferably at least 60 HV3, when the hardness is measured according to EN ISO 6507-1:2005 (E).

[0030] In one embodiment, the difference between the hardness at any point 0.3 mm below the surface of the rock drill insert and the hardness 1 mm below the surface of the rock drill insert is at least 20 HV3, preferably at least 35 HV3, more preferably at least 40 HV3, more preferably at least 45 HV3, when the hardness is measured according to EN ISO 6507-1:2005 (E).

[0031] HV3 measurements were performed using a KB30S programmable hardness tester from KB Prueftechnik GmbH as follows: Sectioning along the longitudinal axis of the insert sample Grinding and polishing of the sectioned surface using progressively finer grits and abrasive suspensions Scan the edge of the sample Program the hardness tester to make a series of indentations at specified distances to the edge Programming the distance between individual indents at each distance of 0.3 mm or more from the edge Indentation with a 3kg load at all programmed coordinates The computer moves the stage to each coordinate with an indent, performs auto-exposure and auto-focus, and then automatically measures the size of each indent. The user inspects all indented photos for focus errors or other effects that may lead to invalid results, and manually re-evaluates invalid selections, if any, in each series.

[0032] The average hardness at a particular depth from the surface is defined as the average of at least 50 hardness values measured at that depth evenly distributed around the insert.

[0033] In one embodiment, the average grain size of the cemented carbide is greater than 0.7 μm but less than 18 μm, as measured according to the Jeffries method defined herein. The WC grain size is selected to suit the desired final properties of the cemented carbide (e.g., toughness, strength, wear resistance, and thermal conductivity). According to one embodiment, the average WC grain size is greater than 0.7 μm, or greater than 0.9 μm, or greater than 1 μm, or greater than 1.25 μm, or greater than 1.5 μm, or greater than 1.75 μm, or greater than 2.0 μm. If the WC grain size is too large, the material will be difficult to sinter. Therefore, the average WC grain size is preferably less than 18 μm, or less than 15 μm, or less than 10 μm, or less than 6 μm.

[0034] Micrographs for evaluating WC grain size were acquired using a scanning electron microscope (SEM) with backscattered electron (BSE) contrast. Prior to imaging, material samples were polished using standard procedures and etched with Murakami solution to create contrast at the grain boundaries. The average WC grain size was then evaluated from at least two different micrographs for each material using the Jeffries method described below. An average value was then calculated (for each material) from the average grain size values obtained from the individual micrographs. The procedure for average grain size evaluation using the modified Jeffries method was as follows: Select a rectangular frame of appropriate size so that a minimum of 300 WC particles are included in the SEM micrograph. Manually count the particles within the frame and those intersecting the frame, and obtain the average particle size from equations (2-4): TIFF2025525506000002.tif24170TIFF2025525506000003.tif73170TIFF2025525506000004.tif30170In the formula, d=average particle size of WC (μm) L1, L2 = Frame side length (mm) M=Magnification L scale mm = Scale bar length measured on micrograph (mm) L scale micro = Actual length of scale bar relative to magnification (μm) n1 = number of particles that fit completely within the frame n2 = number of particles crossing the frame boundary wt%Co = known cobalt content (wt%).

[0035] Equation 3 is used to estimate the WC fraction based on the known Co content of the material. Equation 4 then calculates the average WC grain size from the ratio of the total WC area in the frame to the number of grains contained in that frame. Equation 4 also includes a correction factor to compensate for the fact that in a random 2D cross section, not all grains will be cut at their maximum diameter.

[0036] In one embodiment, the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.17, more preferably between 0.065 and 0.16, and even more preferably between 0.075 and 0.15.

[0037] In another embodiment, the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.12, preferably between 0.05 and 0.10.

[0038] According to yet another embodiment, the M7C3 phase is present in the cemented carbide, where M represents a combination of Cr, Co, and W, i.e., (Cr,Co,W)7C3. Co solubility can reach as high as 38 atomic % of the metal content in the M7C3 carbide. The balance of Cr:Co:W is influenced by the overall carbon content in the cemented carbide.

[0039] In another embodiment the cemented carbide insert has a bulk hardness of 1750 HV20 or less, preferably 1700 HV20 or less, more preferably 1650 HV20 or less. The cemented carbide of the rock drill insert suitably has a bulk hardness of at least 800 HV20, or at least 900 HV20, or at least 950 HV20, or at least 1000 HV20. Hardness is measured according to EN ISO 6507-1:2005 (E).

[0040] In another embodiment, the cemented carbide insert comprises <1 area % eta phase, preferably <0.8 area % eta phase. The amount of eta phase is measured by binary image analysis using an optical microscope, measuring 10 random areas and calculating the average area %.

[0041] In another embodiment, the cemented carbide insert is substantially free of eta phase. As used herein, substantially free of eta phase means <0.5 area % eta phase. The amount of eta phase is measured by binary image analysis using an optical microscope, measuring 10 random areas and calculating the average area %.

[0042] In one embodiment, the modified CoM / Co weight % is substantially equal throughout the volume of the cemented carbide insert.

[0043] In one embodiment, the cobalt content is substantially equal throughout the volume of the cemented carbide insert, which can be measured, for example, using EDS.

[0044] In one embodiment, the chromium content is substantially equal throughout the volume of the cemented carbide insert, which can be measured, for example, using EDS.

[0045] In one embodiment, the sintering temperature used is 1350 to 1550°C, preferably 1400 to 1530°C.

[0046] According to one embodiment, the rock drill insert 2 according to the present invention is mounted in a rock drill bit body of a tophammer (TH) equipment, or a down-the-hole (DTH) drilling equipment, or a rotary drilling equipment, or a raise boring pilot bit equipment, or a raise boring cutter equipment, or a push boring (blind boring) equipment, or a mechanical cutting equipment, or a horizontal directional drilling (HDD) equipment. The rotary drilling equipment may be an oil and gas rotary cutter equipment.

[0047] Example 1: Samples The samples listed in Table 1 were produced by grinding WC (dm_FSSS = 1.2–18.0 μm) together with Co and Cr3C2 in a ball mill containing 92% alcohol and 2% polyethylene glycol (PG8000). To adjust the modified CoM / Co wt% ratio to the target value, a small amount of the slurry was removed from the mill, dried, and pressed into a green body. This was sintered in a sintering HIP furnace at 1410 °C for 60 min, with the final 20 min sintered at 55 bar Ar pressure. The modified CoM / Co wt% ratio was measured and calculated as described previously. If the modified CoM / Co wt% ratio was too low, carbon (soot) was added to the mill; if the ratio was too high, very fine tungsten metal powder was added. The amount of soot or tungsten to be added was specifically calculated for each material based on the deviation from the modified CoM / Co wt% target. The slurry was then homogenized by running a ball mill for a short time. The slurry was then spray dried in a N2 atmosphere. The powder was uniaxially pressed to form a green body, which was then sintered as described above to produce inserts. The insert properties were measured using the methods previously described.

[0048] TIFF2025525506000005.tif103170

[0049] Example 2: Uniaxial compression test / plastic deformation Specimens A–F were strained to failure in uniaxial compression at room temperature using an Instron 5989 test frame at a constant crosshead displacement rate (=0.6 mm / min) while recording the load-displacement curves. The test fixture, counterface hardness and parallelism, and specimen geometry conformed to ISO standard 4506:2017 E, "Hardmetals - Compression test." Compliance curves obtained by loading the test fixture without the specimen were subtracted from the load-displacement curves measured directly on the specimen during each measurement, taking into account the elastic deformation of the test rig and loading string. Engineering stresses were calculated from the load values by dividing the load by the initial minimum cross-sectional area, obtained from the minimum diameter measured on each individual test specimen before testing. To isolate only the plastic deformation of the material, the elastic deformation of the specimen was subtracted from the stress-displacement curves during post-processing of the test data using linear regression. Separation of plastic deformation from the stress-displacement curves was performed as follows: A linear regression was applied to the part of the data set corresponding to the initial section of the stress-displacement curve that was visually assumed to be linear. Next, we calculate the variance range of this partial data set used for linear regression using the fit R 2 The value was varied to maximize it. The first derivative of the regression equation (the slope of the fitted line) was used to calculate the plastic deformation from the measured total displacement using the relationship in Equation 5: e plast = e - σ / a Equation 5 During the ceremony, "e plast " represents the plastic deformation, "e" represents the displacement measured after subtraction of the compliance curve, "σ" represents the engineering stress, and "a" represents the coefficient corresponding to the slope of the line fitted to the elastic part of the stress-displacement curve by linear regression, as described above.

[0050] Figure 2 shows a comparison of the deformation curves in uniaxial compression for samples A and B (i.e., samples with 11 wt% Co), with sample A (comparison sample) shown as a solid line and sample B (sample according to the invention) shown as a dashed line.

[0051] 3 shows a comparison of the deformation curves in uniaxial compression for samples C and D (i.e., samples with 13.5 wt. % Co), with sample C (comparison sample) shown as a solid line and sample D (sample according to the invention) shown as a dashed line.

[0052] 4 shows a comparison of the deformation curves in uniaxial compression for samples E and F (i.e., samples with 6 wt. % Co), with sample E (comparison sample) shown as a solid line and sample F (sample according to the invention) shown as a dashed line.

[0053] The deformation curves in Figures 2 to 4 were plotted from a plastic deformation of 0.001 mm.

[0054] Inventive samples B and D exhibit more significant strain hardening (i.e., steeper deformation curves) throughout the majority of the deformation to failure; higher ultimate compressive strength (UCS); and significantly greater plasticity (plastic deformation to failure) compared to comparative samples A and C. This effect is present not only when the binder phase content is equal, but also when the average tungsten carbide grain size is equal for the samples, as shown in Figure 3.

[0055] Inventive sample F exhibits higher ultimate compressive strength (UCS) and more pronounced strain hardening compared to comparative sample E. This effect is present not only for samples with equal binder phase content, but also for samples with equal average tungsten carbide grain size, as shown in Figure 4. This, along with the properties of samples B-D, demonstrates that the inventive effect is present over a wide range of cobalt contents and grain sizes.

[0056] Example 3: Abrasion resistance test Rock drill bit inserts (10 mm outer diameter, hemispherical top geometry) were ground from all eight materials (A, B, C, D, E, F, G, and H) and subjected to wear tests in a continuous water stream, using a rotating granite log counterface as the insert / rock contact target. Insert / rock contact was maintained during the test by applying a constant force of 10 kgf (98 N). Because only the cylindrical portion of the insert was ground, the portion of the insert in contact with the rock surface was in a sintered state in all cases. While the granite log was rotating, the insert was moved along the granite log at a constant feed rate of 0.9 mm / s, with a total sliding distance between 432 and 446 m. All inserts were carefully weighed before and after testing. The volumetric wear per unit of sliding distance was then calculated for each material from the measured mass loss and density. Three inserts were tested for each of the eight materials (A, B, C, D, E, F, G, and H), and the average volumetric wear per unit of sliding distance was calculated from the three tests. The results are shown in Table 2 below.

[0057] TIFF2025525506000006.tif64170

[0058] Less volumetric wear (higher wear resistance) was recorded for each of the samples according to the invention. In particular, material D was found to have less volumetric wear than material C, despite the same nominal binder content, the same average WC particle size, and a lower room temperature hardness. Material F was found to have less volumetric wear than material E, despite the same nominal binder content and the same average WC particle size.

[0059] Example 4: Field Test The tophammer bits were fabricated with an initial bit diameter of approximately 49 mm and six 10 mm diameter peripheral inserts and three 8 mm diameter front inserts. The insert geometry was conical, with a semi-ballistic top radius of 3.5 mm. Three bits with peripheral inserts of Sample E and three bits with peripheral inserts of Sample F were tested. The front inserts were of the standard material (WC-Co 6%) for all tested bits. During drilling, one bit with Sample E inserts was lost, leaving two bits for comparison. The bits were tested in medium-hard and medium-abrasive granite at the Hammarby Sjoestad construction site in Stockholm, Sweden. The drill rig was equipped with a COP3038 rock drill operating at full power with 30 kW impact power and a 100 Hz impact frequency. These bits were drilled until the drilling rate indicated that they needed to be resharpened to continue drilling. Average results from 2-3 bits are shown in Table 3 below.

[0060] TIFF2025525506000007.tif71170

[0061] It can be seen that the performance of the insert according to the invention is improved over the comparative insert.

Claims

1. A rock drill insert (2) comprising a cemented carbide body containing a hard component of WC in a binder phase containing cobalt, The aforementioned cemented carbide, 4-18% by weight of Co, - Cr such that the Cr / Co mass ratio in the innermost part of the rock drill insert is 0.04 to 0.19 • Remaining WC and unavoidable impurities It contains, The content of the binder phase in the cemented carbide is substantially equal throughout the entire rock drill insert. The hardness measured according to EN ISO 6507-1:2005 (E) is at least 800 HV20. The average WC grain size of the aforementioned cemented carbide is greater than 0.7 μm but less than 18 μm, as measured according to the Jeffries method specified herein. Rock drill insert (2), The rock drill insert (2) has a modified CoM / Co weight% ratio between 0.70 and 0.81 and is substantially free of the eta phase, where the eta phase is M ６ C or M １２ C is C, and in the formula M = (Co, W, Cr), The modified CoM / Co weight% ratio is, Modified CoM / Co weight % = (Co magnetic % + 1.13 x Cr weight %) / Co weight % It is calculated according to, Here, Co magnetic% is the weight percentage of magnetic Co, and Co weight% and Cr weight% are the weight percentages of Co and Cr in the cemented carbide, respectively, which are measured according to the methods specified herein. A rock drill insert (2) characterized by the following.

2. The rock drill insert (2) according to claim 1, wherein the cobalt content is between 8 and 18% by weight.

3. The rock drill insert (2) according to claim 1, wherein the cobalt content is between 4 and 8% by weight.

4. The rock drill insert (2) according to claim 1, wherein the modified CoM / Co weight% is between 0.73 and 0.

79.

5. The rock drill insert (2) according to claim 1, wherein the difference between the average hardness of the rock drill insert at 0.3 mm below the surface and the average hardness of the innermost part of the rock drill insert, measured according to EN ISO 6507-1:2005 (E), is at least 30 HV3.

6. The rock drill insert (2) according to claim 1, wherein the difference between the hardness at any point 0.3 mm below the surface of the rock drill insert and the hardness at 1 mm below the surface of the rock drill insert, measured according to EN ISO 6507-1:2005 (E), is at least 20 HV3.

7. The rock drill insert (2) according to claim 1, wherein the average value of the WC grain size of the cemented carbide is 1 μm or more, but less than 10 μm.

8. The rock drill insert (2) according to claim 1, wherein the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.

17.

9. The rock drill insert (2) according to claim 8, wherein the mass ratio Cr / Co in the cemented carbide is between 0.065 and 0.

16.

10. The rock drill insert (2) according to claim 9, wherein the mass ratio Cr / Co in the cemented carbide is between 0.075 and 0.

15.

11. The rock drill insert (2) according to claim 8, wherein the mass ratio Cr / Co in the cemented carbide is between 0.05 and 0.

12.

12. The rock drill insert (2) according to claim 1, wherein the hardness of the innermost part of the carbide alloy is 1750 HV20 or less.

13. The rock drill insert (2) according to claim 1, wherein the modified CoM / Co weight% ratio is substantially equal over the entire volume of the rock drill insert (2).

14. A rock drill bit body to which one or more rock drill inserts (2) according to any one of claims 1 to 13 are attached.

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