tip

Abstract

This disclosure relates to a cemented carbide impact tip for a road milling pick, a road milling pick comprising the same, use of the road milling pick, and a method of manufacturing the cemented carbide impact tip.

Description

[0001] PF1628-WO-0-ORD

[0002] TIP

[0003] Field of the invention

[0004] This invention relates to a cemented carbide impact tip for a road milling pick, a road milling pick comprising the same, use of the road milling pick, and a method of manufacturing the cemented carbide impact tip.

[0005] Background

[0006] Cemented carbides are used in a wide variety of applications, particularly in applications where a tool needs to be resistant against wear and other mechanical degradation. As one example, cemented carbide impact tips are widely used as tools for mechanical picks for degrading roads (“road milling picks” or “road planing picks”). Cemented carbides used in degrading roads may be subjected to high impact loads, intensive wear, severe fatigue, high temperatures and strong thermal shocks in use, and are typically engineered to possess an outstanding combination of hardness and fracture toughness, as well as associated properties of high strength and abrasion resistance. Typically, abrasion resistance is positively correlated with hardness.

[0007] A method of enhancing the hardness of the surface layer of a cemented carbide body is disclosed in WO 2010 / 097784. In the method disclosed in WO 2010 / 097784, the carbon content close to the surface of the impact tip is increased by carburisation. In this process, a green body comprising the desired porosity is formed by pre-sintering of a suitable mixture of tungsten carbide, binder precursor, and other components. The pre-sintered green body is then exposed to an atmosphere containing a carbon-containing gas, such as methane. The porosity of the green body is such that the carbon-containing gas is able to infiltrate and enrich the surface of the tip with carbon but does not penetrate into the core region of the tip. During sintering, the carbon gradient leads to a hardness gradient being formed, where the surface layer of the impact tip is harder than its core. Cemented carbides of this structure are often referred to as “functionally graded carbides”.

[0008] To establish the carbon gradient in the impact tip, the porosity of the green body has to be such that the carbon-containing gas is not able to fully penetrate the green body. If the gas fully penetrates the green body, then no carbon gradient will be formed during the sintering stage. This means that carburisation is only suitable for finer grades of tungsten carbide powders. PF1628-WO-0-ORD

[0009] This presents a problem in the context of road milling picks. Ultra-coarse grain tungsten carbide is typically used in road milling picks as it provides better fracture toughness, heat resistance and thermal cycling properties than finer grades. However, because of the high porosity of green bodies of ultra-coarse grain tungsten carbide prior to sintering, it is not possible to form functionally graded carbide impact tips for road milling using the conventional carburisation method, as the gas permeates the whole tip.

[0010] It is an object of the invention to provide a solution to the above-mentioned problem.

[0011] Summary of the invention

[0012] In a first aspect, the invention provides a cemented carbide impact tip for a road milling pick, comprising; a strike surface and an attachment surface distal to the strike surface; wherein the impact tip has a longitudinal axis and the strike surface and the attachment surface are spaced apart along the longitudinal axis; and a cylindrical portion or a frustoconical portion with a cone angle of less than 20° and which extends in the direction of the longitudinal axis away from the strike surface; wherein the impact tip comprises a first region having a first mean hardness and a first boundary, wherein the first region comprises the strike surface and a first part of the cylindrical portion or frustoconical portion; and the first boundary is substantially perpendicular to the longitudinal axis; a second region having a second mean hardness and a second boundary, wherein the second region comprises the attachment surface and a second part of the cylindrical portion or frustoconical portion and the second boundary is substantially perpendicular to the longitudinal axis; and the first boundary and the second boundary are part of the cylindrical portion or the frustoconical portion, wherein the first mean hardness is greater than the second mean hardness; and wherein the cemented carbide comprises a metal carbide and a binder phase, wherein the binder phase comprises at least one of cobalt, nickel and iron.

[0013] As an option, the strike surface is configured to impact a road.

[0014] As an option, the attachment surface is configured to attach the impact tip to a support body of a road milling pick.

[0015] As an option, the impact tip further comprises a transition region directly between the first boundary and the second boundary. PF1628-WO-0-ORD

[0016] As used herein, carbon content refers to the mean carbon concentration within the binder phase. The carbon content does not include the carbon which forms part of the metal carbide itself, e.g. the carbon in tungsten carbide would be excluded.

[0017] The mean hardness can be measured by taking a series of hardness measurements in the region in question and then taking an arithmetic mean of said measurements. For example, the series of measurements can be taken at intervals along the longitudinal axis.

[0018] As an option, a hardness of the transition region varies substantially monotonically along the longitudinal axis and between the first boundary and the second boundary. The term “monotonically” means that the curve is substantially smooth.

[0019] As an option, a concentration of the binder phase in the first region is lower than a concentration of the binder phase in the second region.

[0020] As an option, the concentration of the binder phase in the first region is up to and including 7 wt.% (of the cemented carbide) and the concentration of the binder phase in the second region is greater than or equal to 8 wt.% (of the cemented carbide).

[0021] As an option, the concentration of the binder phase in the first region is at least 10% lower than the concentration of the binder phase in the second region.

[0022] As an option, a concentration of the binder phase in the transition region varies substantially monotonically along the longitudinal axis and between the first boundary and the second boundary.

[0023] As an option, the first region has a first specific magnetic saturation and the second region has a second specific magnetic saturation, and the first specific magnetic saturation is higher than the second specific magnetic saturation.

[0024] As an option, the specific magnetic saturation of the first region is between 88% and 98%.

[0025] As an option, the specific magnetic saturation of the second region is between 75% and 88%. PF1628-WO-0-ORD

[0026] As an option, the cemented carbide of the impact tip (the first, second and transition regions) is substantially free of free C. By free C (i.e. free carbon) herein it is meant carbon in the cemented carbide body that is present in elemental form, for example in the form of graphite.

[0027] As an option, substantially all the C present in the cemented carbide of the impact tip is in the form of C dissolved in the binder phase and WC.

[0028] As an option, the cemented carbide of the first region is substantially free of eta-phase and free carbon, and the carbon content is such that a magnetic moment of the cemented carbide body is at least 88 percent of the theoretical value of a cemented carbide body comprising a binder phase of nominally pure Co, Ni and / or Fe or a mixture thereof.

[0029] As an option, the cemented carbide of the second region is substantially free of eta-phase and free carbon, and the carbon content is such that a magnetic moment of the cemented carbide body is at most 88 percent of the theoretical value of a cemented carbide body comprising a binder phase of nominally pure Co, Ni and / or Fe or a mixture thereof.

[0030] As an option, the cemented carbide of the first region has a mean grain size of greater than or equal to 3.5 microns, for example greater than or equal to 4 microns, for example greater than or equal to 4.5 microns, for example greater than or equal to 5 microns. The mean grain size is measured according to ISO 4499-2:2020.

[0031] As an option, the cemented carbide of the second region has a mean grain size of greater than or equal to 2.5 microns, for example greater than or equal to 3 microns, for example, greater than or equal to 3.5 microns, for example greater than or equal to 4 microns, for example greater than or equal to 4.5 microns, for example greater than or equal to 5 microns. The mean grain size is measured according to ISO 4499-2:2020.

[0032] As an option, the mean grain size of the first region is higher than the mean grain size of the second region.

[0033] As an option, the first mean hardness is higher than the second mean hardness by at least 30 Vickers units. Vickers Hardness is measured according to ISO 6507-1 :2018 (Metallic materials — Vickers hardness test — Part 1 : Test method).

[0034] As an option, the first mean hardness is greater than or equal to 1200 Vickers units, for example from 1200 Vickers units to 1500 Vickers units. PF1628-WO-0-ORD

[0035] As an option, the second mean hardness is less than or equal to 1200 Vickers units, for example from 1000 Vickers units to 1200 Vickers units.

[0036] As an option, the height of the first region is lower than the height of the second region.

[0037] As an option, the binder phase comprises tantalum-containing inclusions, the tantalum- containing inclusions being carbide nanoparticles or intermetallic nanoparticles, the tantalum-containing inclusions having the shape that is any one of substantially spherical, platelet-like or needle-like, the tantalum content being between 1.5 weight per cent and 15 weight per cent of the binder phase content; and wherein the tantalum-containing inclusions have a mean largest linear dimension of no more than 80 nm.

[0038] As an option, the tantalum content may be between 1.5 weight per cent and 3.5 weight per cent of the binder phase.

[0039] As an option, the tantalum-containing inclusions may have a mean largest linear dimension of no more than 50 nm.

[0040] As an option, the tantalum-containing inclusions may have a mean largest linear dimension of below 20 nm or below 10 nm.

[0041] As an option, the cemented carbide is substantially free of Ta-containing grains having a largest mean linear dimension greater than 200 nm, and preferably greater than 500 nm.

[0042] As an option, the inclusions comprise a material according to the formula TaxWyCozC phase, where x is a value in the range from 1 to 8, y is a value in the range from 0 to 8 and z is a value in the range from 0 to 10.

[0043] As an option, the inclusions comprise any of a cubic q-phase comprising Co6(W,Ta)eC and a hexagonal q-phase comprising Co3(W,Ta)i0C3.

[0044] As an option, the strike surface has a rounded geometry.

[0045] As an option, the rounded geometry is conical, hemispherical, domed, truncated, ballistic or a combination thereof.

[0046] As an option, the strike surface is a spherical dome. PF1628-WO-0-ORD

[0047] As an option, the strike surface is hexagonal, quadrangular or octagonal in lateral crosssection.

[0048] As an option, the impact tip further comprises a tapered portion, wherein the strike surface adjoins the tapered portion, wherein the tapered portion extends in the direction of the longitudinal axis away from the strike surface, and the tapered portion tapers outwardly.

[0049] As an option, the cylindrical portion or the frustoconical portion adjoins the tapered portion or the strike surface.

[0050] As an option, the impact tip further comprises a concave portion which comprises a concave surface which adjoins the cylindrical or frustoconical portion and extends in the direction of the longitudinal axis, wherein the concave surface curves outwardly.

[0051] As an option, the impact tip comprises a conical or ballistic strike surface which adjoins the cylindrical or the frustoconical portion which adjoins the tapered portion and extends in the direction of the longitudinal axis away from the strike surface towards the attachment surface.

[0052] As an option, the first boundary and the second boundary are part of the cylindrical portion or the frustoconical portion.

[0053] As an option, the metal carbide of the cemented carbide of the first region is tungsten carbide and the binder phase of the first region comprises cobalt, and the metal carbide of the cemented carbide of the second region is tungsten carbide and the binder phase of the second region comprises cobalt, and the concentration of cobalt in the binder phase of the first region is lower than the concentration of cobalt in the binder phase of the second region.

[0054] In a second aspect, the invention provides a road milling pick comprising the impact tip as described herein and a support surface to which the attachment surface of the impact tip is attached.

[0055] In a third aspect, the invention provides a use of the road milling pick as described herein in a method of milling a road, wherein the road comprises asphalt or concrete.

[0056] In a fourth aspect, the invention provides a method of manufacturing the impact tip for a road milling pick as described herein, comprising: providing a first precursor mixture comprising a PF1628-WO-0-ORD metal carbide, preferably tungsten carbide, and a binder phase precursor; providing a second precursor mixture comprising a metal carbide, preferably tungsten carbide, and a binder phase precursor, wherein the first precursor mixture has a higher carbon content than the second precursor mixture; inserting an amount of the first precursor mixture into a die configured to form an impact tip for a road milling pick, followed by inserting an amount of the second precursor mixture into the die; pressing the first and second precursor mixtures in the die to form a green body, such that the part of the green body that will form the first region is formed of the first precursor mixture and the part of the green body that will form the second region is formed of the second precursor mixture, and sintering the green body to form a cemented carbide impact tip as described herein.

[0057] As an option, the first precursor mixture is prepared using a wet milling process in which powders are dispersed in a solvent and which produces a slurry comprising the first precursor mixture.

[0058] As an option, the second precursor mixture is prepared using a wet milling process in which powders are dispersed in a solvent and which produces a slurry comprising the second precursor mixture.

[0059] As an option, the method further comprises drying and granulating the slurry (either or both of the slurries comprising the first precursor mixture and the second precursor mixture) to form granules of the precursor mixture for pressing to form a green body.

[0060] As an option, the first precursor mixture comprises tungsten carbide powder as the metal carbide and cobalt powder and carbon black as the binder phase precursor, and the second precursor mixture comprises tungsten carbide powder as the metal carbide and cobalt powder and tungsten metal as the binder phase precursor.

[0061] As an option, the method further comprises pre-sintering the green body at a temperature of from approximately 600°C to approximately 1100°C for a duration of from approximately 5 minutes to approximately 360 minutes.

[0062] As an option, the pre-sintering is performed under vacuum.

[0063] As used herein, a pre-sintered body means an article that has undergone heat treatment and is partially or incompletely sintered, and which is intended to be further sintered. PF1628-WO-0-ORD

[0064] As an option, the sintering is at a temperature of from approximately 1250°C to approximately 1480°C and for a duration of at least 15 minutes.

[0065] As an option, the sintering is performed at a temperature of between 1360°C and 1430°C and / or for a time of from 20 minutes to 120 minutes.

[0066] As an option, the sintering is performed at a temperature of between 1350°C and 1500°C and / or for a time of from 15 minutes to 120 minutes.

[0067] As an option, the sintering is performed for a duration of at least 15 minutes, or at least 30 minutes, or at least 45 minutes, or at least 60 minutes, or at least 75 minutes, or at least 90 minutes, or at least 120 minutes, or at least 150 minutes, or at least 180 minutes, or at least 210 minutes, or at least 240 minutes, or at least 270 minutes, or at least 300 minutes, or at least 330 minutes.

[0068] As an option, the sintering is performed for a duration of no more than 360 minutes, or no more than 330 minutes, or no more than 300 minutes, or no more than 270 minutes, or no more than 240 minutes, or no more than 210 minutes, or no more than 180 minutes, or no more than 150 minutes, or no more than 120 minutes, or no more than 90 minutes, or no more than 75 minutes, or no more than 60 minutes, or no more than 45 minutes, or no more than 30 minutes.

[0069] As an option, the sintering is performed for from approximately 15 minutes to approximately 360 minutes, for example from approximately 15 minutes to approximately 300 minutes, for example from approximately 30 minutes to approximately 240 minutes, for example from approximately 45 minutes to approximately 180 minutes, for example from approximately 60 minutes to approximately 120 minutes, for example from approximately 75 minutes to approximately 90 minutes.

[0070] As an option, the sintering is performed in a vacuum.

[0071] As an option, the sintering is performed in an inert atmosphere, for example in an argon atmosphere.

[0072] As an option, cooling the sintered body is performed in an argon atmosphere. PF1628-WO-0-ORD

[0073] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 3°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0074] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 2°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0075] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1 °C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0076] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1.0°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0077] As an option, the sintered body is cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 0.8°C / min, and then the sintered body is cooled to room temperature at an uncontrolled rate.

[0078] Drawings

[0079] Non-limiting preferred embodiments will now be described with reference to the drawings, of which:

[0080] Figure 1 shows an underside of a typical road-milling machine, incorporating prior art pick tools;

[0081] Figure 2 shows a front perspective view of a prior art pick tool;

[0082] Figure 3 shows a front perspective view of the prior art pick tool of Figure 2 with partial cross-section of the interface between the impact tip and the support body;

[0083] Figure 4 shows a front perspective view of another prior art pick tool;

[0084] Figure 5 outlines a method of manufacturing an impact tip according to the invention; PF1628-WO-0-ORD

[0085] Figure 6 shows a front view of a first impact tip according to the invention;

[0086] Figure 7 shows a front view of a second impact tip according to the invention;

[0087] Figure 8 shows a front view of a third impact tip according to the invention;

[0088] Figure 9 shows a front view of a fourth impact tip according to the invention;

[0089] Figure 10 shows a front view of a fifth impact tip according to the invention;

[0090] Figure 11 shows a plot of Co content and Vickers hardness with respect to the distance from the surface of the impact tip;

[0091] Figure 12 shows a light microscopy image of the first region of the impact tip after sintering; and

[0092] Figure 13 shows a light microscopy image of the second region of the impact tip after sintering.

[0093] Detailed description

[0094] As used herein, a cemented carbide is a material comprising grains of metal carbide such as tungsten carbide (WC) or titanium carbide (TiC), dispersed within a binder phase comprising a metal such as cobalt (Co), nickel (Ni), iron (Fe) and optionally other components as detailed herein, such as tantalum. The binder phase may be said to cement the grains together as a sintered compact, typically having negligible porosity. The most common cemented carbide is Co-cemented WC.

[0095] Figure 1 shows an underside of a typical road-milling machine 10. The milling machine may be an asphalt or pavement planer used to degrade formations such as pavement 12 prior to placement of a new layer of pavement. The milling machine may also be used to mill road surfaces made of concrete. A plurality of pick tools 14 are attached to a rotatable drum 16. The drum 16 brings the pick tools 14 into engagement with the formation 12. A base holder 18 is securely attached to the drum 16 and, by virtue of an intermediate tool holder (not shown), may hold the pick tool 14 at an angle offset from the direction of rotation such that the pick tool 14 engages the formation 12 at a preferential angle. A shank (not shown) of the pick tool 14 is rotatably disposed within the tool holder. PF1628-WO-0-ORD

[0096] Figures 2 and 3 show a prior art pick tool 14. The pick tool 14 comprises a generally bellshaped impact tip 20 and a steel support body 22. The support body comprises a body portion 24 and a shank 26 extending centrally from the body portion 24. The impact tip 20 sits within a circular recess 27 provided in one end of the support body 22. This means that an edge of the steel support body 22 always surrounds the metal carbide impact tip 20. Braze material (not shown), typical provided as a thin circular disc, positioned within the circular recess 27 securely joins the impact tip 20 to the support body 22. The pick tool 14 is attachable to a drive mechanism, for example, of a road-milling machine, by virtue of the shank 26 and a spring sleeve 28 surrounding the shank 26 in a known manner. The spring sleeve 28 enables relative rotation between the pick tool 14 and the tool holder.

[0097] Alternative constructions of pick tool are also available, an example of which is shown in Figure 4. In this embodiment, the pick tool 114 comprises a generally conical impact tip 120 which is inserted into a socket (not shown) in the steel support body 122. The remainder of the body portion 24, shank 26 and spring sleeve 28 are the same as for the above- mentioned embodiment. Pick tool 114 is particularly suited for planing roads made of concrete.

[0098] As noted above, because of the high porosity of ultra-coarse grain tungsten carbide, which is typically used in the manufacture of impact tips for road milling picks, it is not possible to form functionally graded carbide impact tips for road milling using the conventional carburisation method.

[0099] The present inventors have solved this problem by applying a process which will be termed herein as “double filling”, where the “double filling” refers to the filling of the die twice with two different graded powders before pressing. This double filling process provides an impact tip for a road milling pick which is functionally graded. However, the grading differs from that of cemented carbide bodies produced using the above-mentioned carburisation technique. Conventional functionally graded cemented carbides produced by carburisation have a core-shell type structure, with a harder, higher carbon content surface layer surrounding a less hard, lower carbon content core. In the presently disclosed method, the functionally graded cemented carbide comprises a first portion which comprises the strike surface of the impact tip and which has an enhanced mean hardness and higher carbon content, and a second portion which comprises the attachment surface of the impact tip and which has a lower mean hardness and lower carbon content. The first and second portions sandwich a transition layer. Thus, rather than having a hardness gradient inward from all surfaces of the tip, the hardness gradient is from the upper part of the impact tip (i.e. the part PF1628-WO-0-ORD which impacts the road) to the lower part of the impact tip (i.e. the part that is attached to the rest of the road milling pick). The presently disclosed manufacturing method is not simply an alternative method of manufacturing a known product; it is a new method which provides a new product.

[0100] The invention has the advantage of providing an impact tip with the desired gradient of properties while avoiding the deleterious effect on the properties of the cemented carbide that are associated with too little carbon on the one hand (i.e. the formation of eta-phase) and free carbon (i.e. reduction in hardness and fracture toughness) on the other.

[0101] A method of manufacturing an impact tip for a road milling pick in accordance with the invention is outlined in Fig. 5.

[0102] 51. Prepare or provide a first precursor mixture comprising a metal carbide powder and a binder phase precursor.

[0103] The first precursor mixture has a higher carbon content than the second precursor mixture. The first precursor mixture comprises a metal carbide, preferably tungsten carbide powder, preferably ultra-coarse grain for the reasons detailed above, and a binder phase precursor. The binder phase precursor typically comprises cobalt powder but may additionally or alternatively comprise iron or nickel or any combination of iron, nickel and cobalt, and any of the additives detailed below. To enhance the carbon content, a carbon source is also added. An example of a suitable carbon source is carbon black or graphite.

[0104] 52. Prepare or provide a second precursor mixture comprising a metal carbide powder and a binder phase precursor and which has a lower carbon content than the first precursor mixture.

[0105] The second precursor mixture has a lower carbon content than the first precursor mixture. The second precursor mixture comprises a metal carbide, preferably tungsten carbide, powder, preferably ultra-coarse grain for the reasons detailed above, and a binder phase precursor. The binder phase precursor typically comprises cobalt powder but may additionally or alternatively comprise iron or nickel or any combination of iron, nickel and cobalt, and any of the additives detailed below. To decrease the carbon content, W metal is also added. PF1628-WO-0-ORD

[0106] The precursor mixtures can be formed by any suitable method so long as it leads to intimate mixing of the components. For example, a milling step may be used. For example, the milling step may be performed by attrition milling using an attritor or ball milling using a ball mill, e.g. ball milling using tungsten carbide milling balls. The milling is typically a wet milling process, i.e. in which the powder is dispersed in a solvent and which produces a slurry comprising the milled powders. Milling is typically performed in an organic solvent to form a slurry of the milled powders in said solvent. The organic solvent may be selected from the group consisting of hexane, ethanol, toluene, acetone and mixtures thereof. An organic wax may be dispersed or dissolved in the solvent, typically a paraffin wax. The slurry is then dried to form a graded powder mixture. Drying may be followed by granulation. For example, spray-granulation of the slurry may be performed to form granules of the powder mixture for pressing to form the green body.

[0107] As used herein, a green body means an article intended to be sintered, but which has not yet been sintered. It may generally be self-supporting and may have the general form of the intended finished article.

[0108] In addition to the above-mentioned components of the first and second precursor mixtures, either or both of the first and second precursor mixtures may comprise a refractory metal, for example at least one of the following: Ti, V, Cr, Mn, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Re, Os and Ir. The refractory metal may be in the form of a nitride or a carbide. In a particular example, the refractory metal carbide is tantalum carbide, for example as detailed in WO 2019 / 038180 A1 , the entire contents of which are hereby incorporated by reference. Additionally or alternatively, either or both of the first and second precursor mixtures may comprise Si, Ge, Pb, Y or Mn, either in the form of a nitride or a carbide.

[0109] S3. Load a die for forming road milling impact tips into a press, then partially fill the die cavity with the first precursor mixture such that the first precursor mixture forms the strike surface of the resulting impact tip.

[0110] The method of loading the die is not particularly limited so long as the fill level is consistent. The level of filling may be determined by the weight of mixture added to the die. This can be measured using a suitable dosing apparatus, as is typically used in the manufacture of cemented carbides and in other industries.

[0111] The shape of the die is adapted to the particular shape of the impact tip to be formed. Some examples of impact tip shapes are provided below. PF1628-WO-0-ORD

[0112] 54. Fill the remainder of the space in the die cavity with the second precursor mixture.

[0113] Again, the method of loading the die is not particularly limited so long as the fill level is consistent. Again, the level of filling may be determined by the weight of the mixture to be added to the die, which can be measured using a suitable dosing apparatus.

[0114] Industrial manufacturers of cemented carbide products are familiar with the proportion of shrinkage of the green body during sintering and can readily adapt the size of the die and fill level to achieve the desired dimensions of first, second and transition regions in the impact tip.

[0115] 55. Press to obtain a green body.

[0116] The pressing may be, for example, cold isostatic pressing.

[0117] 56. Sinter to obtain a functionally graded cemented carbide impact tip as described herein.

[0118] After pressing, the green body is then sintered to form a sintered cemented carbide body. The sintering may be at a temperature of from approximately 1250°C to approximately 1480°C and for a duration of at least 15 minutes, or at any of the temperatures and times listed above. Sintering may be performed either under vacuum or under a protective atmosphere, such as argon. Alternatively, a first sintering step may be performed under vacuum, followed by a second sintering step performed under an inert, for example argon, atmosphere.

[0119] Without wishing to be bound by a particular hypothesis, it is believed that the method exploits a known phenomenon called “cobalt drift”, in which liquid cobalt within a cemented carbide being sintered tends to migrate in the same direction in which carbon moves. The movement of cobalt can therefore be controlled by setting up a carbon gradient and allowing the carbon to diffuse from a region of high concentration to one of low concentration. In this case, carbon and cobalt diffuse from the first region to the second region, forming a transition region between the first and second regions during sintering. The concentration of cobalt and carbon in the transition region varies monotonically across the transition region and in the direction of the longitudinal axis of the impact tip. An analogous drift is also thought to occur with iron and nickel. PF1628-WO-0-ORD

[0120] The higher binder phase concentration in the second region leads to a higher rate of shrinkage upon cooling from sintering temperatures. As a result, the first region, which contains a lower binder phase concentration has a lower shrinkage rate then the second region. This means that the first region has high residual compressive stresses, which leads to an improved combination of hardness and fracture toughness.

[0121] After sintering, the sintered body is then cooled from the sintering temperature to room temperature. The sintered body may be cooled at a particular cooling rate. For example, the sintered body may be cooled from the sintering temperature to 1100°C at a cooling rate of from approximately 0.1 °C / min to approximately 1.0°C / min, and then the sintered body may be cooled to room temperature at an uncontrolled rate.

[0122] Different shapes of impact tips can be formed by using suitably shaped dies.

[0123] A first example impact tip 220 which can be formed by the above method is depicted schematically in Figure 6.

[0124] Impact tip 220 comprises a strike surface 30 and an attachment surface 70 distal to the strike surface 30. Impact tip 220 has a longitudinal axis L. The strike surface 30 and the attachment surface 70 are spaced apart along the longitudinal axis L. It should be noted that the term “strike surface” is not intended to suggest that only this surface is configured to contact the road to be milled, merely that it is the primary function of this surface of the impact tip. Impact tip 220 further comprises a first region 40 having a first mean hardness and a first boundary 40a. The first region 40 comprises the strike surface 30 and the first boundary 40a is substantially perpendicular to the longitudinal axis L. The impact tip 220 further comprises a second region 60 having a second mean hardness and a second boundary 60a. The second region 60 comprises the attachment surface 70 and the second boundary 60a is substantially perpendicular to the longitudinal axis. The impact tip 220 further comprises a transition region 50 directly between the first boundary 40a and the second boundary 60a. In other words, the first region 40, transition region 50 and second region 60 are contiguous with each other. The strike surface 30 is configured to impact a road. In this example, the strike surface 30 has a conical shape. The conical strike surface 30 adjoins a cylindrical portion 65 which extends in the direction of the longitudinal axis L away from the strike surface 30 towards the attachment surface 70. The first region 40 comprises a first part of the cylindrical portion 65, and the second region 60 comprises a second part of the cylindrical portion 65. The first boundary 40a and the second boundary 60a are part of the cylindrical portion 65 of the strike tip 220. In other words, the first PF1628-WO-0-ORD boundary 40a, the second boundary 60a are completely contained within the cylindrical portion 65. As a consequence of this, the transition region 50 is also completely contained within the cylindrical portion 65. This means that the harder first portion is found in the area of the impact tip which is exposed to the most wear, thereby extending the life of the pick. In this embodiment, the second region 60 is also completely contained within the cylindrical portion 65. This tool is particularly suited to breaking concrete. The attachment surface 70 is configured to attach the impact tip 220 to a support body of a road milling pick, for example that depicted in Figure 4.

[0125] While in this and the following embodiments, a cylindrical portion 65 is shown, this could be replaced with a frustoconical portion with a cone angle of less than 20°.

[0126] In this embodiment, the hardness of the transition region 50 varies substantially monotonically along the longitudinal axis L and between the first boundary 40A and the second boundary 60a.

[0127] Impact tip 320 is depicted in Figure 7. Impact tip 320 is the same as impact tip 220, except that impact tip 320 has a ballistic strike surface 30 rather than the conical strike surface of impact tip 220. The ballistic strike surface ensures the best performance in concrete milling.

[0128] Impact tip 420 is depicted in Figure 8. Impact tip 420 is the same as impact tips 220 and 320, except that it further comprises a tapered portion 90, and the strike surface 30 has a different shape as explained below. The strike surface 30 adjoins the tapered portion 90. The tapered portion 90 extends in the direction of the longitudinal axis L away from the strike surface 30, and the tapered portion tapers outwardly. The strike surface 30 at the tip of the impact tip 420 is in the form of a spherical cap.

[0129] Impact tip 520 is depicted in Figure 9. Impact tip 520 is the same as impact tip 420, except that it further comprises a concave portion 100 which has a concave surface 100a. The concave portion 100 adjoins the cylindrical portion 65 and extends in the direction of the longitudinal axis L. The concave surface 100a curves outwardly. Impact tip 520 further differs from impact tip 420 in that it is configured for attachment to a support body as depicted in Figures 2 and 3, rather than attachment via a socket as in the pick tool depicted in Figure 4.

[0130] Impact tip 620 is depicted in Figure 10. Impact tip 620 is the same as impact tip 520, except that it further comprises a protective skirt potion 110. The protective skirt portion 110, and PF1628-WO-0-ORD indeed the whole impact tip, may have the structure as described in WO 2020 / 109207 A1 (see in particular Figures 6-10 of that document, and accompanying text in the description), the entire contents of which are hereby incorporated by reference.

[0131] Various parameters of the tip can be measured as shown in Figures 6-10. Possible values for those parameters are provided below.

[0132] The height of the impact tip, Ht, is the longest longitudinal dimension of the impact tip as measured along the longitudinal axis from the extremity of the strike surface 30 to the extremity of the attachment surface 70. The height of the tip, Ht, may be at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm, or at least 16 mm, or at least 17 mm, or at least 18 mm, or at least 19 mm, or at least 20 mm. The height of the tip, Ht, may be at most 50 mm, or at most 45 mm, or at most 40 mm, or at most 35 mm, at most 30 mm, or at most 29 mm, or at most 28 mm, or at most 27 mm, or at most 26 mm, or at least 25 mm, or at most 24 mm, or at most 23 mm. The height of the tip, Ht, may be in the range of from approximately 5 mm to approximately 50 mm, for example from approximately 10 mm to approximately 50 mm, for example from approximately 5 mm to approximately 30 mm, for example from approximately 10 mm to approximately 30 mm, for example from approximately 10 mm to approximately 25 mm.

[0133] The height of the top portion of the impact tip, Hi, is measured along the longitudinal axis from the boundary with the conical portion 65 to the extremity of the strike surface 30. The height of the top portion of the impact tip, Hi, may be at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm, or at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm. The height of the top portion of the impact tip, Hi, may be at most 11 mm, or at most 10 mm, or at most 9 mm, or at most 8 mm, or at most 7 mm, or at most 6 mm, or at most 5 mm. The height of the top portion of the impact tip, Hi, may be in the range of from approximately 1 mm to approximately 10 mm, for example from approximately 4 mm to approximately 10 mm, for example from approximately 1 mm to approximately 5 mm, for example from approximately 2 mm to approximately 5 mm.

[0134] The height of the cylindrical or frusto-conical portion of the impact tip, H2, is measured along the longitudinal axis from the boundary with top portion of the impact tip to the upper boundary of an adjoining non-cylindrical or frusto-conical portion, if present. The height of the cylindrical or frusto-conical portion of the impact tip, H2may be at least 1 mm, or at least 2 mm, or at least 3 mm, or at least 4 mm, or at least 5 mm, or at least 6 mm, or at least 7 PF1628-WO-0-ORD mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The height of the cylindrical or frusto-conical portion of the impact tip, H2, may be at most 20 mm, or at most 19 mm, or at most 18 mm, or at most 17 mm, or at most 16 mm, or at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm, or at most 9 mm, or at most 8 mm, or at most 7 mm. The height of the cylindrical or frusto-conical portion of the impact tip, H2, may be in the range of from approximately 1 mm to approximately 20 mm, for example from approximately 1 mm to approximately 15 mm, for example from approximately 4 mm to 10 mm, for example from approximately 5 mm to approximately 8 mm.

[0135] The height of the first portion 40 of the impact tip, H3, is measured along the longitudinal axis from the extremity of the strike surface 30 to the first boundary 40a. The height of the first portion 40 of the impact tip, H3, may be at least 2 mm, or at least 3 mm, or at least 4 mm, or at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The height of the first portion 40 of the impact tip, H3, may be at most 20 mm, or at most 19 mm, or at most 18 mm, or at most 17 mm, or at most 16 mm, or at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm, or at most 9 mm, or at most 8 mm, or at most 7 mm. The height of the first portion 40 of the impact tip, H3, may be in the range of from approximately 2 mm to approximately 20 mm, for example from approximately 2 mm to approximately 10 mm, for example from approximately 4 mm to 10 mm, for example from approximately 4 mm to approximately 7 mm.

[0136] The height of the transition portion 50 of the impact tip, H4, is measured along the longitudinal axis from the first boundary 40a to the second boundary 60a. The height of the transition portion 50 of the impact tip, H4, may be at least 0.1 mm, or at least 0.2 mm, or at least 0.3 mm, or at least 0.4 mm, or at least 0.5 mm, or at least 0.6 mm, or at least 0.7 mm, or at least 0.8 mm, or at least 0.9 mm, or at least 1 mm, or at least 1.1 mm, or at least 1.2 mm, or at least 1 .3 mm, or at least 1 .4 mm, or at least 1 .5 mm. The height of the transition portion 50 of the impact tip, H4, may be at most 3 mm, or at most 2.9 mm, or at most 2.8 mm, or at most 2.7 mm, or at most 2.6 mm, or at most 2.5 mm, or at most 2.4 mm, or at most 2.3 mm, or at most 2.2 mm, or at most 2.1 mm, or at most 2 mm. The height of the transition portion 50 of the impact tip, H4, may be in the range of from approximately 0.1 mm to approximately 3 mm, for example from approximately 0.5 mm to approximately 2 mm, for example from approximately 1 mm to approximately 3 mm, for example from approximately 1 mm to approximately 2 mm. PF1628-WO-0-ORD

[0137] The height of the second portion 60 of the impact tip, H5, is measured along the longitudinal axis from the extremity of the attachment surface 70 to the second boundary 60a. The height of the second portion 60 of the impact tip, H5, may be at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The height of the second portion 60 of the impact tip, H5, may be at most 25 mm, or at most 24 mm, or at most 23 mm, or at most 22 mm, or at most 21 mm, or at most 20 mm, or at most 19 mm, or at most 18 mm, or at most 17 mm, or at most 16 mm, or at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm. The height of the second portion 60 of the impact tip, H5, may be in the range of from approximately 5 mm to approximately 25 mm, for example from approximately 5 mm to approximately 20 mm, for example from approximately 10 mm to approximately 15 mm.

[0138] The height of the spherical cap portion 80 of the impact tip, H6, is measured along the longitudinal axis from a line drawn in 2D projection perpendicular to the longitudinal axis and which connects with the ends of the tapered portion to the extremity of the spherical cap portion 80. The height of the spherical cap portion 80 of the impact tip, He, may be at least 0.1 mm, or at least 0.2 mm, or at least 0.3 mm, or at least 0.4 mm, or at least 0.5 mm, or at least 0.6 mm, or at least 0.7 mm, or at least 0.8 mm, or at least 0.9 mm, or at least 1 mm, or at least 1.1 mm, or at least 1.2 mm, or at least 1.3 mm, or at least 1.4 mm, or at least 1.5 mm. The height of the spherical cap portion 80 of the impact tip, He, may be at most 3 mm, or at most 2.9 mm, or at most 2.8 mm, or at most 2.7 mm, or at most 2.6 mm, or at most 2.5 mm, or at most 2.4 mm, or at most 2.3 mm, or at most 2.2 mm, or at most 2.1 mm, or at most 2 mm. The height of the spherical cap portion 80 of the impact tip, H6, may be in the range of from approximately 0.1 mm to approximately 3 mm, for example from approximately 0.5 mm to approximately 2 mm, for example from approximately 1 mm to approximately 2 mm.

[0139] The height of the concave portion 100 of the impact tip, H7, is measured along the longitudinal axis from the base of the cylindrical or frusto-conical portion to a line drawn in 2D projection perpendicular to the longitudinal axis and which connects with the ends of the concave portion. The height of the concave portion 100 of the impact tip, H7, may be at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The height of the concave portion 100 of the impact tip, H7, may be at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm. The height of the concave portion 100 of the impact tip, H7, may be in the range of PF1628-WO-0-ORD from approximately 5 mm to approximately 15 mm, for example from approximately 5 mm to approximately 10 mm.

[0140] The height of the protective skirt portion 110 of the impact tip, H8, is measured along the longitudinal axis from the base of the concave portion to the extremity of the attachment surface 70. The height of the protective skirt portion 110 of the impact tip, H8, may be at least 0.1 mm, or at least 0.2 mm, or at least 0.3 mm, or at least 0.4 mm, or at least 0.5 mm, or at least 0.6 mm, or at least 0.7 mm, or at least 0.8 mm, or at least 0.9 mm, or at least 1 mm, or at least 1.1 mm, or at least 1 .2 mm, or at least 1 .3 mm, or at least 1 .4 mm, or at least 1.5 mm. The height of the protective skirt portion 110 of the impact tip, H8, may be at most 3 mm, or at most 2.9 mm, or at most 2.8 mm, or at most 2.7 mm, or at most 2.6 mm, or at most 2.5 mm, or at most 2.4 mm, or at most 2.3 mm, or at most 2.2 mm, or at most 2.1 mm, or at most 2 mm. The height of the protective skirt portion 110 of the impact tip, H8, may be in the range of from approximately 0.1 mm to approximately 3 mm, for example from approximately 0.5 mm to approximately 2 mm, for example from approximately 1 mm to approximately 2 mm.

[0141] The diameter of the spherical cap, dc, is the longest linear dimension of the spherical cap measured perpendicular to the longitudinal axis L. The diameter of the spherical cap, dc, may be at least 1 mm, or at least 1.1 mm, or at least 1 .2 mm, or at least 1 .3 mm, or at least 1 .4 mm, or at least 1.5 mm, or at least 1 .6 mm, or at least 1 .7 mm, or at least 1 .8 mm, or at least 1 .9 mm, or at least 2.0 mm. The diameter of the spherical cap, dc, may be at most 4 mm, or at most 3.9 mm, or at most 3.8 mm, or at most 3.7 mm, or at most 3.6 mm, or at most 3.5 mm, or at most 3.4 mm, or at most 3.3 mm, or at most 3.2 mm, or at most 3.1 mm, or at most 3 mm, or at most 2.9 mm, or at most 2.8 mm, or at most 2.7 mm, or at most 2.6 mm, or at most 2.5 mm, or at most 2.4 mm, or at most 2.3 mm, or at most 2.2 mm, or at most 2.1 mm, or at most 2 mm. The diameter of the spherical cap, dc, may be in the range of from approximately 1 mm to approximately 4 mm, for example from approximately 2 mm to approximately 4 mm, for example from approximately 2 mm to approximately 3.5 mm.

[0142] The diameter of the impact tip, dt, is the longest linear dimension of the impact tip measured perpendicular to the longitudinal axis L. The diameter of the impact tip, dt, may be at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The diameter of the impact tip, dt, may be at most 30 mm, or at most 29 mm, or at most 28 mm, or at most 27 mm, or at most 26 mm, or at most 25 mm, or at most 24 mm, or at most 23 mm, or at most 22 mm, or at most 21 mm, or at most 20 mm, or at most 19 mm, PF1628-WO-0-ORD or at most 18 mm, or at most 17 mm, or at most 16 mm, or at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm. The diameter of the impact tip, dt, may be in the range of from approximately 5 mm to approximately 30 mm, for example from approximately 5 mm to approximately 25 mm, for example from approximately 10 mm to approximately 25 mm, for example from approximately 10 mm to approximately 20 mm.

[0143] The diameter of the cylindrical portion, di, is the longest linear dimension of the cylindrical portion measured perpendicular to the longitudinal axis L. The diameter of the cylindrical portion, di, may be at least 5 mm, or at least 6 mm, or at least 7 mm, or at least 8 mm, or at least 9 mm, or at least 10 mm, or at least 11 mm, or at least 12 mm, or at least 13 mm, or at least 14 mm, or at least 15 mm. The diameter of the cylindrical portion, di, may be at most 50 mm, or at most 45 mm, or at most 40 mm, or at most 35 mm, or at most 30 mm, at most 25 mm, or at most 24 mm, or at most 23 mm, or at most 22 mm, or at most 21 mm, or at most 20 mm, or at most 19 mm, or at most 18 mm, or at most 17 mm, or at most 16 mm, or at most 15 mm, or at most 14 mm, or at most 13 mm, or at most 12 mm, or at most 11 mm, or at most 10 mm. The diameter of the cylindrical portion, di, may be in the range of from approximately 5 mm to 40 mm, for example approximately 5 mm to approximately 25 mm, for example from approximately 10 mm to approximately 25 mm, for example from approximately 10 mm to approximately 20 mm.

[0144] In the embodiments depicted in Figures 6-8, the diameter of the impact tip, dt, is equal to the diameter of the cylindrical portion, di.

[0145] In the embodiments depicted in Figures 6-10, the first mean hardness is greater than the second mean hardness, the impact tip is made from cemented carbide which comprises a metal carbide and a binder phase, and the binder phase contains at least one of cobalt, nickel and iron. As detailed above, this hardness gradient is the result of drift of cobalt, nickel and / or iron from the higher carbon content first region to the lower carbon content second region.

[0146] For example, the first mean hardness is greater than or equal to 1200 Vickers units, for example from 1200 Vickers units to 1500 Vickers units, and the second mean hardness is less than or equal to 1200 Vickers units, for example from 1000 Vickers units to 1200 Vickers units. The first mean hardness may be higher than the second mean hardness by at least 30 Vickers units, for example at least 40 Vickers units, for example at least 50 Vickers units, for example at least 60 Vickers units, for example at least 70 Vickers units, for PF1628-WO-0-ORD example at least 80 Vickers units, for example at least 90 Vickers units, for example at least 100 Vickers units.

[0147] As noted above, the content of binder phase and C within cemented carbides can be determined by selection of the starting powders. The C content within the binder phase can be decreased by adding W metal or increased by adding carbon black to the precursor mixtures.

[0148] As used herein, the term “metal” means a metal in elemental form or an alloy having typical metallic properties, such as electrical conductivity.

[0149] The magnetic properties of the cemented carbide can be related to structural and compositional characteristics, including the content of carbon present in the binder phase. As is well known in the art, the content of carbon within the binder phase of cemented tungsten carbide can be measured indirectly, by measuring the concentration of tungsten dissolved in the binder phase to which it is indirectly proportional: the higher the content of carbon dissolved in the binder phase the lower the concentration of tungsten dissolved in the binder phase. As used herein, the magnetic moment o of a material is in units of microTesla times cubic metre per kilogram of the material. The tungsten content within the binder phase can be determined from a measurement of the magnetic moment, o or magnetic saturation, p = 4KO, these values having an inverse relationship with the tungsten content (Roebuck (1996), “Magnetic moment (saturation) measurements on hard-metals”, Int. J. Refractory Met., Volume 14, pp. 419-424.). The specific magnetic saturation (SMS) is the percentage of magnetic saturation in comparison with that of nominally pure Co, Ni, or Fe or mixture thereof, depending on the binder phase composition, and is also related to the carbon content, as is known in the art.

[0150] The binder phase cobalt, iron and / or nickel content within a cemented carbide can be measured by various methods well known in the art, including indirect methods such as such as the magnetic properties of the cemented carbide or more directly by means of EDX, but the most accurate method is based on chemical leaching of Co, Fe and / or Ni. The mean grain size of carbide grains, such as WC grains, can be determined by examination of SEM (scanning electron micrographs) or light microscopy images of metallurgically prepared cross-sections of a cemented carbide body, applying the mean linear intercept technique as detailed in ISO 4499-2:2020, for example. Alternatively, the mean size of the WC grains can be measured indirectly by measuring the magnetic coercivity of the cemented carbide, which PF1628-WO-0-ORD indicates the mean free path of Co, Fe and / or Ni intermediate the grains, from which the WC grain size may be calculated using a simple formula well known in the art. This formula quantifies the inverse relationship between magnetic coercivity of a cemented WC and the Co, Fe and / or Ni mean free path, and consequently the mean WC grain size.

[0151] Several phases comprising tungsten (W), cobalt (Co) and carbon (C) are known and are typically designated by Greek letters. An eta-phase composition is understood herein to mean a carbide compound having the general formula MxM’yCz, where M is at least one element selected from the group consisting of W, Mo, Ti, Cr, V, Ta, Hf, Zr, and Nb; M’ is at least one element selected from the group consisting of Fe, Co, Ni, and C is carbon. Where M is tungsten (W) and M’ is cobalt (Co), as is the most typical combination, then eta-phase is understood herein to mean Co3W3C (eta-1) or Co6W6C (eta-2), as well as fractional sub- and super-stochiometric variations thereof. After sintering, the impact tip is substantially devoid of eta phase. As used herein, the phrase “substantially devoid of’ means that if an amount of a certain material, substance or phase is detectable within a cemented carbide body, the amount is so small that it has no material discernible effect on the performance of the cemented carbide body at elevated temperatures, for example 700 to 800 degrees centigrade.

[0152] The cemented carbides of the first region, transition region, and second region comprise at least WC grains, a binder phase comprising Co, Ni, Fe, or any combination thereof, C dissolved in the binder phase, and inevitable impurities. Further additives can be added as desired, as noted above. Thus, the cemented carbides of the first region, transition region, and second region may further comprise W, Ta, Ti, V, Cr, Mn, Zr, Nb, Mo, Ru, Rh, Hf, Re, Os, Ir, Si, Ge, Pb, Y, Mn, and / or N.

[0153] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of WC grains, a Co, Ni and / or Fe-based binder phase with dissolved W and C, and unavoidable impurities.

[0154] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of WC grains, a Co, Ni and / or Fe-based binder phase with dissolved W and C and tantalum-containing inclusions, and unavoidable impurities.

[0155] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of 90-98 wt.% WC grains, 1-10 wt.% combined Co, Ni and / or Fe, 0-5 wt.% W, 0-5 wt.% Ta, 0-5 wt.% Ti, 0-5 wt.% V, 0-5 wt.% Cr, 0-5 wt.% Mn, 0-5 PF1628-WO-0-ORD wt.% Zr, 0-5 wt.% Nb, 0-5 wt.% Mo, 0-5 wt.% Ru, 0-5 wt.% Rh, 0-5 wt.% Hf, 0-5 wt.% Re, 0- 5 wt.% Os, 0-5 wt.% Ir, 0-5 wt.% Si, 0-5 wt.% Ge, 0-5 wt.% Pb, 0-5 wt.% Y, 0-5 wt.% Mn, 0-5 wt.% N, remainder C and unavoidable impurities.

[0156] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of 90-98 wt.% WC grains, 1-10 wt.% combined Co, Ni and / or Fe, 0-3 wt.% W, 0-3 wt.% Ta, 0-3 wt.% Ti, 0-3 wt.% V, 0-3 wt.% Cr, 0-3 wt.% Mn, 0-3 wt.% Zr, 0-3 wt.% Nb, 0-3 wt.% Mo, 0-3 wt.% Ru, 0-3 wt.% Rh, 0-3 wt.% Hf, 0-3 wt.% Re, 0- 3 wt.% Os, 0-3 wt.% Ir, 0-3 wt.% Si, 0-3 wt.% Ge, 0-3 wt.% Pb, 0-3 wt.% Y, 0-3 wt.% Mn, 0-3 wt.% N, remainder C and unavoidable impurities.

[0157] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of 90-98 wt.% WC grains, 1-10 wt.% Co, 0-5 wt.% Ni, 0- 5 wt.% Fe, 0-5 wt.% W, 0-5 wt.% Ta, 0-5 wt.% Ti, 0-5 wt.% V, 0-5 wt.% Cr, 0-5 wt.% Mn, 0-5 wt.% Zr, 0-5 wt.% Nb, 0-5 wt.% Mo, 0-5 wt.% Ru, 0-5 wt.% Rh, 0-5 wt.% Hf, 0-5 wt.% Re, 0- 5 wt.% Os, 0-5 wt.% Ir, 0-5 wt.% Si, 0-5 wt.% Ge, 0-5 wt.% Pb, 0-5 wt.% Y, 0-5 wt.% Mn, 0-5 wt.% N, remainder C and unavoidable impurities.

[0158] The first region, transition region, and / or second region of the cemented carbide impact tip may consist of or consist essentially of 90-98 wt.% WC grains, 1-10 wt.% Co, 0-5 wt.% Ni, 0- 5 wt.% Fe, 0-3 wt.% W, 0-3 wt.% Ta, 0-3 wt.% Ti, 0-3 wt.% V, 0-3 wt.% Cr, 0-3 wt.% Mn, 0-3 wt.% Zr, 0-3 wt.% Nb, 0-3 wt.% Mo, 0-3 wt.% Ru, 0-3 wt.% Rh, 0-3 wt.% Hf, 0-3 wt.% Re, 0- 3 wt.% Os, 0-3 wt.% Ir, 0-3 wt.% Si, 0-3 wt.% Ge, 0-3 wt.% Pb, 0-3 wt.% Y, 0-3 wt.% Mn, 0-3 wt.% N, remainder C and unavoidable impurities.

[0159] The cemented carbide of the first region may comprise up to 7 wt.% Co, for example from 4 wt.% to 7 wt.% Co.

[0160] The cemented carbide of the second region may comprise greater than or equal to 7 wt.% Co, for example greater than or equal to 8 wt.% Co, for example greater than or equal to 9 wt.% Co, for example from 9 wt.% to 10 wt.% Co.

[0161] The cemented carbide of the first region may comprise up to 7 wt.% combined Co, Ni and Fe, for example from 4 wt.% to 7 wt.% combined Co, Ni and Fe.

[0162] The cemented carbide of the second region may comprise greater than or equal to 7 wt.% combined Co, Ni and Fe, for example greater than or equal to 8 wt.% combined Co, Ni and PF1628-WO-0-ORD

[0163] Fe, for example greater than or equal to 9 wt.% combined Co, Ni and Fe, for example from 9 wt.% to 10 wt.% combined Co, Ni and Fe.

[0164] In some embodiments, the cemented carbide comprises a concentration of Cr, V, Ta, Ti, Nb, Zr, Hf or Mo in carbide form or in solid solution within the metal binder phase. In some embodiments, the concentration is at most about 2 weight percent at most about 0.5 weight percent, or at most about 0.3 weight percent. In one embodiment, the concentration of Cr, V, Ta, Ti, Nb, Zr, Hf or Mo in carbide form or in solid solution within the binder phase preferably is substantially uniformly distributed throughout the first, transition and second regions.

[0165] The first region, transition region and / or second region of the cemented carbide impact tip may comprise from approximately 90 wt.% to approximately 98 wt.% WC, for example from approximately 75 wt.% to approximately 95 wt.% WC, for example from approximately 80 wt.% to approximately 95 wt.% WC, for example from approximately 85 wt.% to approximately 95 wt.% WC, for example from approximately 90 wt.% to approximately 95 wt.% WC.

[0166] The cemented carbide may include tantalum-containing inclusions as detailed in WO 2019 / 038180 A1 , the entire contents of which are hereby incorporated by reference.

[0167] Example 1

[0168] Two graded powders with differing carbon contents were milled according to the procedure described below. Impact tips were then manufactured by pressing and sintering, and the magnetic properties of the impact tips were measured.

[0169] The batch with a low carbon content (the second precursor mixture) was made in the following way. Tungsten carbide powder with a mean grain size of about 5 pm was milled with 6.2 wt.% Co powder, 1 wt.% W-metal powder and 1 .8 wt.% paraffin wax. The addition of tungsten metal is necessary to obtain the mixture with the low total carbon content. The mixture was produced by milling the powders together for 24 hours by means of a ball mill in a milling medium of hexane using a powder-to-balls ratio of 1 :6.

[0170] The batch with a high carbon content (the first precursor mixture) was made in a similar way as the batch with the low carbon content. The only difference was that instead of adding W- metal, 0.05 wt.% carbon black was added to the powder mixture, along with a further 0.95 wt.% WC. PF1628-WO-0-ORD

[0171] The first and second precursor mixtures were afterwards dried. Then, a green body formed from the first precursor mixture and a green body formed from the second precursor mixture were pressed. The green bodies were then sintered at 1390°C for 45 min, including a 15 min vacuum sintering stage and a 30 min high isostatic pressure (HIP) sintering stage carried out in an argon atmosphere at a pressure of 40 bars. The microstructure of the sintered products formed from the first and second precursor mixtures were free of q-phase and graphite. The magnetic saturation of the sintered product formed from the first precursor mixture was equal to 116.8 Gcm3 / g, which corresponds to a specific magnetic saturation value of 93%. The magnetic saturation of the sintered product formed from the second precursor mixture was equal to 97.9 Gcm3 / g, which corresponds to a specific magnetic saturation value of 78%.

[0172] To investigate the properties of an impact tip formed from the first and second precursor mixtures, the two graded powders were pressed in a press to obtain a green body of an impact tip formed from two different graded powders. In this example, the impact tip has the shape as shown in Figure 10. The upper part of the tip was pressed from the powder batch with the high carbon content with a height of nearly 7 mm, which formed the first region of about 6 mm after liquid-phase sintering; the rest of the tip was pressed from the powder batch with the low carbon content. Before sintering, there is no gradient present in the green body; the gradient (i.e. the transition region) is formed during sintering.

[0173] The green tip comprising the two parts of various graded powders was sintered at 1390°C for 45 min, including a 15 min vacuum sintering stage and a 30 min high isostatic pressure (HIP) sintering stage carried out in an argon atmosphere at a pressure of 40 bars.

[0174] To examine the Co and hardness gradients and microstructure of the sintered tip, the sintered tip was EDM cut in the middle. Figure 11 shows the hardness gradient (labelled “a”) and the Co gradient (labelled “b”) in the tip formed as a result of the Co drift from the part with the higher carbon content into the part with lower carbon content. By distance from surface, it is meant the distance along the longitudinal axis from the tip of the strike surface. As can be seen in Fig. 11 , the tip comprises a first region (labelled “1”), with higher hardness and lower Co content, a second region (labelled “2”) with lower hardness and higher Co content, and a third, transition region (labelled “3”), where the Co content increases monotonically going from the first region to the second region and the hardness decreases monotonically going from the first region to the second region. Specifically, the Co content increases monotonically with depth from the upper extremity of the strike surface from approximately 4-6 wt.% in the first region which has a higher carbon content up to PF1628-WO-0-ORD approximately 9-10 wt.% in the second region, which has a lower carbon content. As a result, the hardness of the first region of the impact tip (which has a higher carbon content), which comprises the strike surface, is significantly higher (in this case by approximately 60 H 10) than that of the second region of the impact tip (which has a lower carbon content).

[0175] In Figure 12, the microstructure of the first region (higher carbon content) is shown, while in Figure 13, the microstructure of the second region (lower carbon content) is shown. It can be seen that neither the first nor the second regions comprise inclusions of ri-phase and free carbon, and that the microstructure of the second region is finer and characterized by a significantly higher binder phase content than that of the first region.

[0176] A pilot batch of the impact tips manufactured according to the method of Example 1 was produced, and these impact tips were used to manufacture road-planing picks. The picks were then field-tested in asphalt milling and compared with a batch of standard road-planing picks which were formed of a single grade of cemented tungsten carbide with cobalt binder phase. The results indicated that the picks with the tips according to the invention achieved substantially lower wear in comparison to standard road-planing picks.

Claims

PF1628-WO-0-ORDClaims1 . A cemented carbide impact tip for a road milling pick, comprising; a strike surface and an attachment surface distal to the strike surface; wherein the impact tip has a longitudinal axis and the strike surface and the attachment surface are spaced apart along the longitudinal axis; and a cylindrical portion or a frustoconical portion with a cone angle of less than 20° and which extends in the direction of the longitudinal axis away from the strike surface; wherein the impact tip comprises: a first region having a first mean hardness and a first boundary, wherein the first region comprises the strike surface and a first part of the cylindrical portion or frustoconical portion and the first boundary is substantially perpendicular to the longitudinal axis; and a second region having a second mean hardness and a second boundary, wherein the second region comprises the attachment surface and a second part of the cylindrical portion or frustoconical portion and the second boundary is substantially perpendicular to the longitudinal axis; and the first boundary and the second boundary are part of the cylindrical portion or the frustoconical portion; wherein the first mean hardness is greater than the second mean hardness; and wherein the cemented carbide comprises a metal carbide and a binder phase, wherein the binder phase comprises at least one of cobalt, nickel and iron.

2. The impact tip of claim 1 , further comprising a transition region directly between the first boundary and the second boundary.

3. The impact tip of claim 2, wherein a hardness of the transition region varies substantially monotonically along the longitudinal axis and between the first boundary and the second boundary.

4. The impact tip of any one of the preceding claims, wherein the first mean hardness is higher than the second mean hardness by at least 30 Vickers units.

5. The impact tip of any one of the preceding claims, wherein the height of the first region is lower than the height of the second region.

6. The impact tip of any one of the preceding claims, wherein a concentration of the binder phase in the first region is lower than a concentration of the binder phase in the second region.

7. The impact tip of any one of the preceding claims, wherein a concentration of the binder phase in the transition region varies substantially monotonically along the longitudinal axis and between the first boundary and the second boundary.PF1628-WO-0-ORD8. The impact tip of any one of the preceding claims, wherein the first region has a first specific magnetic saturation and the second region has a second specific magnetic saturation, and the first specific magnetic saturation is higher than the second specific magnetic saturation.

9. The impact tip of any one of the preceding claims, wherein the cemented carbide of the first region has a mean grain size of greater than or equal to 3.5 microns.

10. The impact tip of any one of the preceding claims, wherein the mean grain size of the cemented carbide of the first region is greater than the mean grain size of the cemented carbide of the second region.11 . The impact tip of any one of the preceding claims, wherein the strike surface has a rounded geometry.

12. The impact tip of claim 11 , wherein the rounded geometry is conical, hemispherical, domed, truncated, ballistic or a combination thereof.

13. The impact tip of claim 11 or claim 12, wherein the strike surface is a spherical dome.

14. The impact tip of any one of claims 1 to 10, wherein the strike surface is hexagonal, quadrangular or octagonal in lateral cross-section.

15. The impact tip of any one of claims 11 to 14, further comprising a tapered portion, wherein the strike surface adjoins the tapered portion, wherein the tapered portion extends in the direction of the longitudinal axis away from the strike surface, and the tapered portion tapers outwardly.

16. The impact tip of claim 15, wherein the cylindrical portion or the frustoconical portion adjoins the tapered portion or the strike surface.

17. The impact tip of any one of the preceding claims, further comprising a concave portion which comprises a concave surface which adjoins the cylindrical or frustoconical portion and extends in the direction of the longitudinal axis, wherein the concave surface curves outwardly.

18. The impact tip of any one of claims 1 to 10, comprising a conical or ballistic strike surface which adjoins the cylindrical or frustoconical portion which adjoins the tapered portion and extends in the direction of the longitudinal axis away from the strike surface towards the attachment surface.

19. The impact tip of any one of the preceding claims, wherein the metal carbide of the cemented carbide of the first region is tungsten carbide and the binder phase of the first region comprises cobalt, and wherein the metal carbide of the cemented carbide of the second region is tungsten carbide and the binder phase of the second region comprises cobalt, and wherein the concentration of cobalt in the binder phase of the first region is lower than the concentration of cobalt in the binder phase of the second region.PF1628-WO-0-ORD20. A road milling pick comprising the impact tip of any one of the preceding claims and a support surface to which the attachment surface of the impact tip is attached.

21. Use of the road milling pick of claim 20 in a method of milling a road, wherein the road comprises asphalt or concrete.

22. A method of manufacturing the impact tip for a road milling pick of any one of claims 1-19, comprising: providing a first precursor mixture comprising a metal carbide and a binder phase precursor; providing a second precursor mixture comprising a metal carbide and a binder phase precursor, wherein the first precursor mixture has a higher carbon content than the second precursor mixture; inserting an amount of the first precursor mixture into a die configured to form an impact tip for a road milling pick, followed by inserting an amount of the second precursor mixture into the die; pressing the first and second precursor mixtures in the die to form a green body, such that the part of the green body that will form the first region is formed of the first precursor mixture and the part of the green body that will form the second region is formed of the second precursor mixture, and sintering the green body to form a cemented carbide impact tip as defined in any one of claims 1-19.

23. The method of claim 22, wherein the first precursor mixture and / or the second precursor mixture is prepared using a wet milling process in which powders are dispersed in a solvent and which produces a slurry comprising the first precursor mixture.

24. The method of claim 23, further comprising drying and granulating the slurry to form granules of the precursor mixture for pressing to form a green body.

25. The method of any one of claims 22 to 24, wherein the first precursor mixture comprises tungsten carbide powder as the metal carbide and cobalt powder and carbon black as the binder phase precursor, and wherein the second precursor mixture comprises tungsten carbide powder as the metal carbide and cobalt powder and tungsten metal as the binder phase precursor.

Images