cutting tools

Abstract

The present invention relates to a rotary cutting tool insert comprising a carrier body made of maraging steel and at least one cutting element having at least one cutting edge, the rotary cutting tool insert further comprising a braze joint joining the carrier body and the at least one cutting element, the braze joint comprising Ti, and a Ti-containing bonding layer having a thickness of 0.03 to 5 μm adjacent to the cutting element.

Description

[Technical Field]

[0001] The present invention relates to a rotary cutting tool including a maraging steel carrier body and cutting elements, the carrier body and cutting elements being joined by brazing. The present invention also relates to a method of manufacturing such a rotary cutting tool. [Background technology]

[0002] It is common in the art to fabricate rotary cutting tools, such as drills or end mills for chip-forming machining, from cemented carbide round tool blanks. The geometry of the drill or end mill, such as chip flutes, cutting edges, etc., is achieved by grinding. Grinding is time-consuming and expensive. For this reason, rotary cutting tools can be reconditioned several times by re-grinding worn parts, such as cutting edges, and can also be provided with new coatings.

[0003] Some attempts have been made to replace portions of the rotary cutting tool body, such as the shank portion, with other, less expensive materials. It is also known to have a loose, replaceable top on the drill that is secured by mechanical means, such as a screw.

[0004] It is known in the art to weld or braze cutting elements to a carrier body of a different material than the cutting elements.

[0005] Using steel as a carrier material is usually not considered an option due to issues with brazing steel and its low hardness and / or tensile strength. Because cutting tools are subjected to large forces when used in cutting processes, the brazed joints must be strong, and the carrier body must have an optimal toughness / hardness ratio. Also, the difference in CTE (coefficient of thermal expansion) between steel and materials such as cemented carbide, polycrystalline diamond (PCD), and cubic boron nitride (cBN) can lead to cracks.

[0006] Also, in the case of rotary cutting tools, which are typically provided with cooling channels, joining the cutting elements to the carrier body by brazing can cause the cooling channels to become clogged with brazing material.

[0007] Although cemented carbide appears suitable for use as a carrier body, it still has its drawbacks. For environmental reasons, recycling of cemented carbide is preferred, which is a complex process. Also, cemented carbide is difficult to machine, and extensive grinding or the like is usually required to reach the final shape of the rotary cutting tool.

[0008] While maraging steels perform well in terms of strength, such as brazed joints, they can still have drawbacks as carrier bodies in certain cutting applications because they do not reach the same hardness levels as cemented carbides. Lower hardness translates to lower wear resistance. For example, in drilling, where the workpiece chip strikes the carrier body rather than just the cutting element, the wear resistance of maraging steels may not be sufficiently good.

[0009] SUMMARY OF THE INVENTION It is an object of the present invention to provide a rotary cutting tool having a steel carrier body capable of withstanding forces during metal cutting operations.

[0010] Another object of the present invention is to provide a rotary cutting tool having cutting elements joined to a steel carrier body having high strength braze joints.

[0011] Another object of the present invention is to provide a rotary cutting tool in which the carrier body can be formed with less effort than a carrier body made of cemented carbide.

[0012] Another object of the present invention is to provide a rotary cutting tool in which the carrier body can withstand high levels of wear from the workpiece tip.

[0013] definition As used herein, rotary cutting tool means any circular tool used in chip-forming machining cutting operations. Examples are drills, end mills and reamers.

[0014] Rotary cutting tools (also called solid round tools) typically include a shank portion and a flute portion integral with the shank portion. The flute portion refers to the portion of the rotary cutting tool that has chip grooves formed on its circumferential surface. One or more internal coolant channels can be provided within the rotary cutting tool.

[0015] By cutting element herein is meant the portion of the cutting tool insert that is engaged in the cutting operation, i.e., the portion that includes at least one cutting edge and that contacts the workpiece. The cutting element can have different shapes depending on the cutting application. As an example, the cutting element can constitute the entire top of the rotary cutting tool, see FIG. 1, or the cutting element can be smaller, such as a vein or nib, brazed to the outermost portion of the rotary cutting tool, see FIG. 2.

[0016] By carrier body is meant herein the cutting tool body that does not comprise the cutting elements. The carrier body can have any of the shapes of the rotary cutting tools described above, and preferably includes at least a portion of the groove portion. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a rotary cutting tool including a carrier body, at least one cutting element including at least one cutting edge, and a braze joint joining the carrier body and the at least one cutting element, the braze joint including Ti, the braze joint including a Ti-containing bonding layer having a thickness of 0.03 to 5 μm adjacent to the cutting element. The carrier body is made of maraging steel.

[0018] The cutting elements can be made of any material known in the art of metal cutting, namely, one of cemented carbide, cermet, ceramic, polycrystalline diamond (PCD), or sintered cubic boron nitride (PcBN).

[0019] By ceramic, we mean materials comprising transition metal carbide, nitride or carbonitride particles, such as WC, Si3N4, SiAlON, Al2O3, SiC whiskers, etc., embedded in an oxide ceramic matrix, such as aluminum oxide, where the amount of transition metal carbide, nitride or carbonitride particles is 5-45% by volume. They are typically sintered in a hot isostatic pressing process.

[0020] The cemented carbides used as cutting elements can be made of any cemented carbide known in the art. Cemented carbides include a hard phase embedded in a metallic binder phase matrix.

[0021] By hardmetal it is meant here that at least 50% by weight of the hard phase is WC.

[0022] Suitably, the amount of the metallic binder phase is 3-20% by weight of the cemented carbide, preferably 4-15% by weight. Preferably, the main component of the metallic binder phase is selected from one or more of Co, Ni and Fe, more preferably the main component of the metallic binder phase is Co.

[0023] By "major component" we mean that no other elements are added to form the binder phase, however, if other components, such as Cr, are added, they will necessarily be dissolved in the binder during sintering.

[0024] In one embodiment of the present invention, the cemented carbide may also include other constituents common to cemented carbide elements selected from Cr, Ta, Ti, Nb and V present as elements or as carbides, nitrides or carbonitrides.

[0025] By cermet is meant herein a material comprising hard elements in a metallic binder phase, the hard elements comprising one or more carbides or carbonitrides of Ta, Ti, Nb, Cr, Hf, V, Mo and Zr, such as TiN, TiC and / or TiCN.

[0026] By PCD (polycrystalline diamond) is meant herein a material containing diamond crystals sintered together, with the amount of diamond crystals being between 50 and 100% by volume. The diamond crystals typically have a grain size of 0.5 to 30 μm. PCD may also contain one or more elements selected from Al, Cr, Co, Ni, V, Fe, and Si.

[0027] By PcBN herein is meant a material comprising cBN particles embedded in a metal and / or ceramic binder, the amount of cBN particles being 30-99% by volume. The ceramic binder may include one or more components that are carbides, nitrides, carbonitrides, borides or oxides of elements selected from Co, Ni and groups 4-6 of the periodic table of the elements.

[0028] Polycrystalline diamond (PCD) and sintered cubic boron nitride (PcBN) can be provided as is, so-called "free-standing", or with a cemented carbide support, so-called "carbide-backed". Polycrystalline diamond (PCD) and sintered cubic boron nitride (PcBN) are usually produced by providing a suitable powder mixture which is subjected to a high-temperature, high-pressure (HP / HT) sintering process to form a sintered body (typically 1400°C, 5 GPa).

[0029] When providing a cemented carbide support for polycrystalline diamond (PCD) and sintered cubic boron nitride (PcBN), this is already prepared before the sintering of the polycrystalline diamond (PCD) and sintered cubic boron nitride (PcBN). One way to do this is to use a cup with a cemented carbide disk at the bottom. The cup is then filled with the desired PCD or cBN powder mixture and then sealed. The sealed cup is then subjected to a high-pressure, high-temperature (HPHT) sintering process. The diamond or cBN material is bonded to the cemented carbide during the sintering process. The disk can then be cut into suitable pieces using, for example, a laser or WEDM (wire electrical discharge machining).

[0030] The cemented carbide used as a support for the polycrystalline diamond (PCD) and sintered cubic boron (PcBN) can be made of any cemented carbide common in the art, see definition above.

[0031] The maraging steel preferably contains 8 to 25 wt. % Ni and one or more alloying elements selected from Co, Mo, Ti, Al, and Cr in a total amount of 7 to 27 wt. %, preferably 7 to 23 wt. %. Maraging steel typically contains less carbon than conventional steels, suitably 0.03 wt. % or less carbon. The balance is Fe.

[0032] In one embodiment of the present invention, the maraging steel contains 11-25 wt% Ni, preferably 15-25 wt% Ni. The alloying elements are suitably Co in an amount of 7-15 wt%, preferably Co in an amount of 8.5-12.5 wt%, Mo in an amount of 3-10 wt%, preferably Mo in an amount of 3-6 wt%, Ti in an amount of 0.1-1.6 wt%, preferably Ti in an amount of 0.5-1.2 wt%, Cr in an amount of 0-0.15 wt%, Al in an amount of 0-0.2 wt%, and C in an amount less than 0.03 wt%, with the balance being Fe.

[0033] In one embodiment of the present invention, the maraging steel has a composition of 17 to 19 wt% Ni, 8.5 to 12.5 wt% Co, 4 to 6 wt% Mo, 0.5 to 1.2 wt% Ti, 0 to 0.15 wt% Cr, 0 to 0.2 wt% Al, and less than 0.03 wt% C. The balance is Fe.

[0034] In another embodiment of the present invention, the maraging steel has a composition of 8 to 11 wt% Ni, preferably 9 to 10 wt% Ni, 2.5 to 4 wt% Cr, preferably 3 to 3.5 wt% Cr, 3.5 to 5 wt% Mo, preferably 4 to 4.5 wt% Mo, 0.4 to 1.1 wt% Ti, preferably 0.7 to 0.9 wt% Ti, less than 0.4 wt% Si, less than 0.4 wt% Mn, and the balance Fe.

[0035] As with all alloys, maraging steels may also contain unavoidable impurities. By impurity, we mean any element that may be present in the maraging steel in such a small amount that it does not have any effect on the properties of the steel. The total amount of impurities is less than 0.50% by weight, preferably less than 0.15% by weight. Examples of such elements are Mn, P, Si, B, and S.

[0036] In one embodiment of the present invention, the amount of Mn is less than 0.05 wt%, the amount of P is less than 0.003 wt%, the amount of Si is less than 0.004 wt%, and S is less than 0.002 wt%.

[0037] The average hardness of the maraging steel parts depends on whether an aging / nitriding step has been performed (see below).

[0038] In one embodiment of the present invention, the carrier body made of maraging steel is not gradient in hardness with an average hardness of 300 to 1200 HVl, preferably 500 to 1100 HVl. The standard deviation of the hardness values ​​is suitably 0 to 150 HVl, preferably 0 to 100 HVl.

[0039] In one embodiment of the present invention, the carrier body made of maraging steel has a hardness gradient, i.e., the carrier body has an increased hardness in the surface region compared to the core. By this, it is meant herein that the hardness has a maximum value at the surface and then gradually decreases toward the core. The carrier body made of maraging steel has an average core hardness of 300 to 700 HVl, preferably 500 to 700 HVl. The standard deviation of the core hardness values ​​is suitably 0 to 20 HVl, preferably 0 to 15 HVl. Thus, the surface of the maraging steel has an average surface hardness of 300 to 1200 HVl, preferably 500 to 1100 HVl. The standard deviation of the hardness values ​​is suitably 0 to 150 HVl, preferably 0 to 100 HVl. The surface hardness is at least 30% higher than the core hardness, preferably at least 40% higher than the core hardness.

[0040] By "core" herein is meant the inner portion of the maraging steel carrier body, where the hardness no longer changes when measured in cross section.

[0041] The depth of the hardness gradient measured from the surface, the nitriding depth, is determined by creating a hardness depth curve on the cross section of a maraging steel carrier with a hardness gradient and measuring HV 0.3 or HV 0.5 according to standard DIN EN ISO 6507-1 from near the surface towards the core until the hardness stops changing. The nitriding depth is given by the vertical distance from the surface of the nitrided carrier body to the point of limiting hardness, which is defined as the average core hardness + 50 HV 0.3 or 50 HV 0.5, see Figure 4.

[0042] The average nitriding hardness depth of the maraging steel carrier body is 0.001 to 0.8 mm, preferably 0.01 to 0.3 mm. The standard deviation of the hardness values ​​is suitably 0 to 0.03 mm, preferably 0 to 0.02 mm.

[0043] Increasing the hardness of the surface of the maraging steel carrier improves its wear resistance, which can be a great advantage when the cutting tool insert according to the invention is used in cutting applications where chips from the workpiece material strike the maraging steel carrier.

[0044] The brazing technique is so-called active brazing. This means that the joint is not formed simply by melting the filler material to form a metallurgical bond, but also involves a chemical reaction with one or both of the materials being joined. The joining element in the filler material is usually Ti, but elements such as Hf, V, Zr, and Cr are also considered active elements. According to the present invention, Ti is the active element.

[0045] As used herein, braze joint means the area or mass between the cemented carbide and the maraging steel component that is filled with filler material and formed during the brazing process, see below.

[0046] The thickness of the brazed joint is suitably 5 to 200 μm, preferably 15 to 100 μm.

[0047] The brazed joint is not a homogeneous phase. Instead, after brazing, the elements in the filler material form different alloy phases.

[0048] The brazed joint includes a Ti-containing bond layer adjacent to the cutting element after brazing. Ti is highly reactive and reacts with one or more elements present in the cutting element during brazing. Most commonly, covalent bonds are formed with one or more of carbon, nitrogen, oxygen, and boron, forming a strong Ti-containing bond layer at the interface between the brazed joint and the cutting element.

[0049] The composition of the Ti-containing bonding layer varies depending on the material of the cutting element, but is typically TiC, TiN, or TiO. x and TiB xThe resulting bonding layer is ceramic, and if the layer growth is not controlled, the bond may become brittle.

[0050] For example, if the material closest to the brazed joint is PCD (polycrystalline diamond) or cemented carbide, the entire cutting element is made of cemented carbide, or it is a carbide-backed PCD or PcBN cutting element, the Ti-containing bonding layer is a TiC layer. The Ti in the brazed joint reacts with the carbon in the WC or diamond to form TiC.

[0051] Another example is when the cutting element is made of solid (also called "free-standing") PcBN, the bonding layer is formed by the Ti reacting with the nitrogen in the PcBN but retaining a small amount of TiB, e.g., TiB2. x It can also contain TiN.

[0052] If the cutting element is made of ceramic, for example an Al2O3 / WC sintered ceramic composite, the bonding layer will be a TiC / TiOx layer.

[0053] There are several ways to detect the presence of a bond layer, depending on the type of equipment used.

[0054] When a scanning electron microscope (SEM) with sufficiently high resolution is used, the bonding layer is clearly visible adjacent to the cutting element. To verify the layer's composition, SEM-EPMA (Electron Probe Microscopy Analysis) with SEM-EDS (Energy Dispersive Spectroscopy) and / or WDS (Wavelength Dispersive Spectroscopy) can be used to identify individual elements within the bonding layer.

[0055] In one embodiment of the present invention, the thickness of the bonding layer is 0.03 to 5 μm, preferably 0.05 to 1 μm, more preferably 0.05 to 0.5 μm, and most preferably 0.05 to 0.25 μm.

[0056] If the SEM image used does not have sufficient resolution to detect the bond layer, the accumulation of Ti and / or C at the interface between the filler material and the cutting element can be seen, for example, using SEM-EDS with WDS or SEM-EPMA. The accumulation of Ti, referred to herein as the Ti accumulation layer, is one indicator that a bond layer has formed, even if it is not visually detectable in the SEM image. The Ti accumulation layer is significantly thicker than the actual bond layer, which is because all the Ti is in the TiC / TiN / TiO x This may mean that TiBx does not form. The thickness of the Ti accumulation layer is also partially affected by the analytical method.

[0057] Preferably, the brazed joint further comprises, in addition to Ti, one or more elements selected from Ag, Cu, Sn, In, Zr, Hf and C, more preferably one or more elements selected from Ag, Cu and In.

[0058] The brazed joint may also contain small amounts of other elements that are considered unavoidable impurities. By unavoidable impurities, we mean small amounts of elements other than those mentioned above that may be present in the brazing material before the brazing process, as well as elements from the materials being joined, such as Co, W, etc. from cemented carbide, and Fe, Ni, etc. from maraging steel. As the temperature increases during the brazing process, small amounts of elements from the joint will inevitably dissolve in the brazing material, causing the brazing material to melt and diffuse out of the joint. As long as the brazing process parameters, such as temperature and time, are within the ranges set forth in this invention, the total amount of unavoidable impurities is small enough not to affect the performance of the brazed joint.

[0059] The composition of a brazed joint after brazing is difficult to determine because the elements are not uniformly distributed. The easiest way, if available, is to look at the filler material used, as pastes or foils are homogeneous blends. Brazed joints may also contain small amounts of elements from the materials being joined, such as Co, W from cemented carbides, and Fe, Ni from maraging steels.

[0060] The amount of Ti and possibly further elements in the brazed joint can also be measured using energy dispersive X-ray spectroscopy (EDS). However, due to the non-uniform distribution of precipitated elements in the brazed joint, many measurement points must be used, resulting in a large standard deviation. Preferably, the brazed joint contains, on average, Ag in an amount of 30-80 wt%, preferably 40-75 wt%, Cu in an amount of 15-50 wt%, preferably 15-40 wt%, Ti in an amount of 0.3-15 wt%, preferably 0.5-5 wt%, Sn in an amount of 0-10 wt%, preferably 0-2 wt%, and In in an amount of 0-30 wt%, preferably 5-25 wt%.

[0061] At the interface between the brazed joint and the maraging steel part, Ti also accumulates at the brazed joint, forming a metallurgical bond with the iron in the steel. The thickness of the Ti accumulation layer on the maraging steel surface is preferably 1 to 10 μm, preferably 2 to 5 μm, and can be measured, for example, by EDS.

[0062] In one embodiment of the present invention, the cutting element constitutes the upper portion of the rotary cutting tool, also referred to as the head. This means that the cutting element includes at least one cutting edge and a portion of the flute portion. If the rotary cutting tool is provided with one or more cooling channels, the cooling channels pass through both the carrier body and the cutting element. An example of such a rotary cutting tool can be seen in FIG. 1.

[0063] In one embodiment of the present invention, the cutting element is a nip or vein. An example of such a rotary cutting tool can be seen in FIG.

[0064] The present invention also relates to a method for manufacturing the above cutting tool, the method comprising the steps of: providing a carrier body made of maraging steel; providing at least one cutting element including at least one cutting edge; disposing a filler material in contact between the carrier body and the cutting element, the filler material including Ti in an amount of 0.3-15% by weight of the filler material; subjecting the carrier body and the cutting element with the filler material therebetween to a brazing process in a furnace at a temperature of 600-830°C for a time of 1-60 minutes, wherein the brazing is carried out in a vacuum.

[0065] The filler material (also referred to as brazing metal) according to the present invention contains Ti in an amount of 0.3 to 15 wt %, preferably 1 to 5 wt %, based on the total weight of the filler material. The filler material of the present invention suitably has a solidus temperature of 490 to 1125°C, preferably 600 to 700°C. Furthermore, the filler material of the present invention has a liquidus temperature of 610 to 1180°C, preferably 700 to 750°C. In addition to Ti, the filler material further contains one or more elements selected from Ag, Cu, Sn, In, Zr, Hf, and Cr.

[0066] In one embodiment of the present invention, the filler material comprises Ag in an amount of 30-80 wt%, preferably 40-75 wt%, Cu in an amount of 15-50 wt%, preferably 15-40 wt%, Ti in an amount of 0.3-15 wt%, preferably 0.5-5 wt%, Sn in an amount of 0-10 wt%, preferably 0-2 wt%, and In in an amount of 0-30 wt%, preferably 5-25 wt%.

[0067] Suitably the filler material is provided as a foil or a paste.

[0068] The filler material is provided on the interface between the cutting element and the maraging steel carrier.

[0069] The thickness of the filler material applied to the joining surfaces before the brazing process depends on the type of material: foil or paste. If a paste is used, enough material is applied so that the surfaces to be brazed are covered. Typically, the thickness is between 5 and 200 μm, preferably between 15 and 100 μm.

[0070] The components, i.e., the cutting element and maraging steel carrier with the filler material sandwiched therebetween, are then placed in a furnace with an inert or reducing environment, i.e., a minimal amount of oxygen. Preferably, the brazing temperature in the furnace is 600-830°C, preferably 650-820°C, more preferably 700-750°C.

[0071] The choice of brazing temperature depends on several things: for example, if the cutting elements are made of PCD, the brazing temperature should be below 750°C to avoid graphitization of the diamond, but if the cutting elements are made of cemented carbide, the widest temperature range mentioned above can be used.

[0072] The time the parts are exposed to high temperature is 1 to 60 minutes, preferably 5 to 15 minutes. If the time at high temperature is too short, the brazed joint will not have enough time to form and for the Ti to react and achieve the desired strength of the brazed joint. If the time at high temperature is too long, the Ti-containing brittle reaction zone will grow uncontrollably, adversely affecting joint properties, such as shear strength.

[0073] Brazing is suitably carried out in a vacuum or in the presence of a low partial pressure of argon. As used herein, a vacuum is defined as a furnace pressure of 5×10 -4 less than mbar, preferably 5×10 -5 mbar. If argon is present, the argon pressure is less than 1×10 -2 It is less than mbar.

[0074] The brazing furnace used in accordance with the present invention can be any furnace capable of providing well-controlled conditions with respect to evacuation, heating and cooling rates, etc., as described above.

[0075] In one embodiment of the present invention, the parts are subjected to an ageing step after the brazing step by subjecting the brazed parts to an elevated temperature of 300-600°C, preferably 350-500°C, most preferably 400-440°C, for a period of 5 minutes to 12 hours, preferably 30 minutes to 8 hours, more preferably 3-6 hours.

[0076] Suitably, the heating rate to the ageing temperature is from 1 to 50°C / min, preferably from 5 to 10°C / min. Suitably, the cooling rate from the ageing temperature to a temperature at least below the solidus temperature of the filler material, preferably below 300°C, is from 1 to 50°C / min, preferably from 5 to 10°C / min.

[0077] In one embodiment of the present invention, aging occurs immediately after the brazing step in the same furnace in which the brazing step occurs.

[0078] In one embodiment of the present invention, aging occurs immediately after the brazing process in a furnace different from the vacuum brazing.

[0079] In one embodiment of the present invention, aging is performed in the same furnace / deposition chamber before or during the deposition of the coating.

[0080] The aging process increases the overall hardness of the maraging steel.

[0081] In one embodiment of the present invention, the aging step is carried out at least partially in a nitriding atmosphere. Due to the temperature during nitriding, there is also an aging effect, so if nitriding is performed, there is usually no additional separate aging step.

[0082] The nitriding step can be carried out using plasma nitriding or gas nitriding, preferably plasma nitriding. The nitriding atmosphere can be provided by a nitrogen-containing gas, such as N2, NH3.

[0083] In one embodiment of the present invention, the nitriding step is carried out using plasma nitriding. By this, it is meant herein that the nitriding is carried out in a vacuum vessel equipped with a plasma generator capable of providing a nitriding atmosphere. The temperature may suitably be 300-600°C, preferably 350-550°C, and the duration may be 1-100 hours. The pressure should preferably be low, suitably 50-600 Pa. For plasma nitriding, the gas is preferably N2, which may be mixed with, for example, H2.

[0084] In one embodiment of the present invention, the nitriding step is carried out using gas nitriding. Gas nitriding is preferably carried out at temperatures between 450 and 600°C, preferably between 500 and 520°C. Gas nitriding is preferably carried out with NH3, which is split into H2 and N2 in a reactor. Gas nitriding can be carried out at low pressure, preferably between 0.05 and 0.02 MPa, or at pressures close to atmospheric pressure.

[0085] The exact temperature, duration and choice of nitriding gas will depend on several things, such as the desired nitriding effect on the maraging steel, the particular type of equipment being used, etc.

[0086] In one embodiment of the present invention, the maraging steel component has a composition of 18-19 wt% Ni, 8-10 wt% Co, 4-6 wt% Mo, 0.5-1.2 wt% Ti, 0-0.15 wt% Cr, 0-0.2 wt% Al, less than 0.03 wt% C, less than 0.04 wt% Si, less than 0.05 wt% Mn, less than 0.003 wt% P, less than 0.002 wt% S, and less than 0.0005 wt% B, with the balance being Fe. The filler material preferably has a composition of 40-75 wt% Ag, 20-40 wt% Cu, 0.5-5 wt% Ti, 0-2 wt% Sn, and 10-25 wt% In.

[0087] In one embodiment of the present invention, the maraging steel component has the following composition by weight: 9-10% Ni, 3-3.5% Cr, 4-4.5% Mo, 0.7-0.9% Ti, less than 0.4% Si, less than 0.4% Mn, and the balance Fe. The filler material preferably has a composition of 40-75% Ag, 20-40% Cu, 0.5-5% Ti, 0-2% Sn, and 10-25% In.

[0088] The most common way to make a rotary cutting tool made only of one material, for example, cemented carbide, is to start with a cylindrical rod that has been ground to its final shape, i.e., with at least one flute and at least one cutting edge. When making a rotary cutting tool according to the present invention, the brazing step can be carried out either before or after the formation of the flute and at least one cutting edge. If the rotary cutting tool is subjected to an aging step with or without nitriding, the formation of the flute and at least one cutting edge, with or without nitriding, is preferably carried out after the brazing step but before the aging step.

[0089] In one embodiment of the present invention, the at least one flute and the at least one cutting edge may be formed prior to the brazing process.

[0090] In one embodiment of the present invention, the rotary cutting tool can be coated with a wear-resistant coating to further enhance cutting performance. The coating can be deposited using PVD or CVD techniques, with PVD being the most common technique for rotary cutting tools. [Brief explanation of the drawings]

[0091] [Figure 1] FIG. 1 shows an exemplary drill in which cutting elements A are the drill head and B are the carrier body of maraging steel with a brazed joint C therebetween. The drill has a shank portion 1, a flute portion 2 with flutes 4, and cooling channels 3. [Figure 2]FIG. 1 shows a drill in which the cutting elements are veins (also called nibs), where cutting element A is the veins and B is the carrier body of maraging steel with a brazed joint C between them (not visible). [Figure 3] FIG. 1 is a schematic diagram of a shear test apparatus, where 1 is the steel part, 2 is the cemented carbide part, and F is the applied force. [Figure 4] FIG. 1 shows an example of a hardness depth curve showing decreasing hardness values ​​from the surface to the core, where A is the average core hardness, B is the limiting hardness, and C is the nitriding depth. [Figure 5] FIG. 1 shows SEM images of the brazed joint showing the interface where A is the cemented carbide, B is the brazed joint, C is the maraging steel carrier, and D is the Ti-containing layer. [Example]

[0092] Example 1 (invention) A cylindrical steel component made of maraging steel 1.2709 was prepared along with a cemented carbide component with a composition of 10 wt.% Co, 1 wt.% other carbides, and the remainder WC. The maraging steel had a hardness of approximately 340 HV1 before brazing.

[0093] The brazing material (Incusil ABA from the WBC group) was provided in the form of a 100 μm thick foil. The brazing material had a composition of 59.0 wt% Ag, 27.5 wt% Cu, 12.5 wt% In, and 1.25 wt% Ti. The solidus temperature was about 605°C and the liquidus temperature was about 715°C.

[0094] A foil was placed between the maraging steel part and the cemented carbide part so that both pieces were in contact with the foil. The assembled joint pieces were then placed in a Schmetz vacuum furnace (type: EU 80 / 1H 30 x 45 x 30 6 bar system *2RV*) and the temperature was initially raised to 740 °C at a rate of 20 °C / min. After holding the brazing temperature of 740 °C for 15 minutes, the pieces were cooled to 300 °C at a rate of 5 °C / min. After 300 °C, they were allowed to cool freely to room temperature.

[0095] Excellent wetting with no signs of thermal stress cracking could be observed and was evidenced by the high shear test results.

[0096] This sample is designated as Invention 1 herein.

[0097] Example 2 (invention) A cylindrical steel component made of maraging steel 1.2709 was prepared along with a cemented carbide component with a composition of 10 wt.% Co, 1 wt.% other carbides, and the remainder WC. The maraging steel had a hardness of approximately 340 HV1 before brazing.

[0098] The brazing material (TB-651 manufactured by Tokyo Blaze) was provided in the form of a 100 μm thick foil. The brazing material had a composition of 65.0 wt% Ag, 28.0 wt% Cu, 2.0 wt% Ti, and 5.0 wt% Sn. The solidus temperature was approximately 700°C, and the liquidus temperature was approximately 750°C.

[0099] A foil was placed between the maraging steel part and the cemented carbide part so that both pieces were in contact with the foil. The assembled joint pieces were then placed in a Schmetz vacuum furnace (type: EU 80 / 1H 30 x 45 x 30 6 bar system *2RV*) and the temperature was initially raised to 815 °C at a rate of 20 °C / min. After holding the brazing temperature of 815 °C for 15 minutes, the pieces were cooled to 300 °C at a rate of 5 °C / min. After 300 °C, they were allowed to cool freely.

[0100] Excellent wetting could be observed with no signs of thermal stress cracking as evidenced by the high shear test results.

[0101] This sample is designated as Invention 2 herein.

[0102] Example 3 (Aging) After the brazing process, the samples of Invention 1 and Invention 2 were subjected to an aging treatment to maintain the hardness of the maraging steel. The pieces were placed in a furnace and the temperature was first increased to 490°C at a rate of 5°C / min. After maintaining the temperature at 580°C for 3 hours, the pieces were cooled to 300°C at a rate of 5°C / min. After 300°C, they were allowed to cool freely. The results are shown in Table 1.

[0103] Example 4 (Plasma Nitriding) The samples according to inventions 1 and 2 were subjected to a plasma nitriding process in a gas flow of 350:50 ml / min H2:N2 at a chamber pressure of 3 mbar. The temperature in the chamber was 490°C and the time the samples were subjected to the plasma nitriding process was 16 hours. No masking of the brazed joints was used before the nitriding treatment. An SEM image of the cross section of the plasma nitrided sample of invention 2 after 16 hours is shown in Figure 5.

[0104] Example 5 (Gas Nitriding) The specimens according to invention 1 were subjected to a gas nitriding process with NH3 splitting. The temperature in the chamber was 510°C, and the specimens were subjected to the gas nitriding process for 23 or 55 hours. No masking of the brazed joints was used before the nitriding treatment.

[0105] Example 6 (Comparative Example) Steel components made of carbon hardened cold work steel 1.2714 were prepared along with cemented carbide components with a composition of 10 wt% Co, 1 wt% other carbides and residual WC.

[0106] The brazing material was provided in the form of a foil with a thickness of 100 μm. The composition of brazing material 1 was Cu 100.0 wt %. The melting temperature was 1085° C.

[0107] A foil was placed between the steel and cemented carbide parts, and the assembled joint pieces were placed in a furnace, where the temperature was first increased to 650 °C at a rate of 20 °C / min and held for 5 min. From 650 °C, the temperature was then increased at a rate of 10 K / min up to the brazing temperature of 1100 °C with a dwell time of 15 min. After the dwell time, free cooling to room temperature was initiated.

[0108] The cemented carbide steel joint with the carbon hardened cold work steel 1.2714 part was then heated by torch to a temperature of 850°C for 10 minutes, then quenched in oil to room temperature, followed by tensile relaxation in a vacuum furnace at 200°C for 2 hours.

[0109] The cemented carbide steel joints with carbon hardened cold work steel 1.2714 components were then aged at 500°C for 2 hours.

[0110] Hereinafter, this sample will be referred to as Comparative Example 1.

[0111] Example 7 The samples were analyzed for shear strength, surface hardness, core hardness and hardness depth curve.

[0112] The shear strength was analyzed by setting up the shearing device as shown in Figure 3. In Figure 3, 1 is a steel part in the form of a steel cylinder (φ = 20 mm, h = 5 mm) and 2 is a carbide part in the form of a carbide cylinder (φ = 10 mm, h = 5 mm). The steel cylinder is placed in the gap of the shear strength testing device, so it can only move in the direction of the load. Notches eroded on the surface of the device hold the joined parts in the correct position and ensure the introduction of an evenly distributed force into the brazed joint. The applied force F was constantly increased until the brazed joint failed and the carbide cylinder was sheared. The relationship between the maximum measured force and the initial joint surface (A = 78.5 mm) was then calculated. 2 The ultimate shear strength was calculated by the quotient of . The brazing material was not removed before determining the shear strength of the brazed joint.

[0113] The nitriding depth for Example 4 was determined by measuring the average nitriding hardness at room temperature. This was done by creating a hardness depth curve by measuring HV 0.3 on a cross section of the nitrided sample according to standard DIN EN ISO 6507-1, starting from the first indentation 0.025–0.1 mm from the edge, and then every 0.03–0.10 mm until the hardness no longer changed. The resulting hardness values ​​were recorded as a function of distance from the surface. From this hardness curve, the nitriding hardness depth was determined as the distance from the surface to the hardness limit (where the hardness limit is the average core hardness (at HV 0.3) + 50 HV 0.3). For Example 5, the nitriding depth was determined in the same way as for Example 3, except that HV 0.5 was used.

[0114] The core hardness shown in Table 1 is HV1 and was measured by a Vickers hardness tester on a cross section of the maraging steel part using a load of 1 kgf (kilogram force) and a loading time of 15 seconds.

[0115] A pattern of five indentations spaced 1.5 mm apart was performed according to the standard and the values ​​shown in Table 1 are the average of the five indentations.

[0116] Surface hardness measurements were performed on the nitrided surface, with at least five indentations spaced 1.5 mm apart, and the values ​​shown in Table 1 are the average of the five indentations. Measurements were performed using a Vickers hardness tester with a load of 1 kgf (kilogram force) and a loading time of 15 s. TIFF2025535605000002.tif70170

[0117] As can be seen in Table 1, nitriding creates a surface that is significantly harder than the core, resulting in improved wear resistance.

Claims

1. A rotary cutting tool, A carrier body; at least one cutting element including at least one cutting edge; a braze joint joining the carrier body and the at least one cutting element, the braze joint comprising Ti, the braze joint comprising a Ti-containing bond layer adjacent the cutting element and having a thickness of 0.03 to 5 μm; The rotary cutting tool, wherein the carrier body is made of maraging steel.

2. The rotary cutting tool of claim 1 , wherein the cutting element is made from one of cemented carbide, ceramic, polycrystalline diamond (PCD), or cubic boron nitride (PcBN).

3. The composition of the Ti-containing bonding layer is TiC, TiN, TiO ｘ and TiB ｘ 3. The rotary cutting tool of claim 1, wherein the material is one of the following:

4. The rotary cutting tool according to any one of claims 1 to 3, wherein the Ti-containing bonding layer has a thickness of 0.05 to 0.5 µm.

5. 5. The rotary cutting tool according to claim 1, wherein the maraging steel comprises 8 to 25 wt. % Ni, one or more alloying elements selected from Co, Mo, Ti, Al, and Cr in a total amount of 7 to 27 wt. %, less than 0.03 wt. % C, and the balance Fe.

6. The rotary cutting tool of claim 1 , wherein the braze joint comprises Cu, Ag, and In.

7. 7. The rotary cutting tool of claim 1, wherein the braze joint comprises Ag in an amount of 30 to 80 wt.%, Cu in an amount of 15 to 50 wt.%, Ti in an amount of 0.3 to 15 wt.%, Sn in an amount of 0 to 10 wt.%, and In in an amount of 0 to 30 wt.%.

8. A rotary cutting tool according to any one of the preceding claims, wherein the carrier body of maraging steel has an average core hardness of 300 to 700 HV1 and an average surface hardness of 300 to 1200 HV1.

9. 9. The rotary cutting tool according to any one of the preceding claims, wherein the maraging steel carrier body is provided with a hardness profile such that the surface hardness is at least 30% higher than the core hardness.

10. The rotary cutting tool of claim 1 , wherein the cutting element is a head including at least a portion of a groove.

11. 11. A method of making the rotary cutting tool of any one of claims 1 to 10, comprising the steps of: providing a carrier body made of maraging steel; providing at least one cutting element including at least one cutting edge; disposing a filler material in contact between the carrier body and the cutting element, the filler material including Ti in an amount of 0.3-15% by weight of the filler material; and subjecting the carrier body and the cutting element with the filler material therebetween to a brazing process in a furnace at a temperature of 600-830°C for a time period of 1-60 minutes, wherein the brazing is performed in a vacuum.

12. The method of claim 11, wherein the carrier body and the cutting elements after the brazing step are subjected to an aging step at a temperature of 300-600° C. for 5 minutes to 12 hours.

13. The method of claim 11, wherein the carrier body and the cutting elements after the brazing step are subjected to a nitriding step at a temperature of 300-600° C. in a nitriding atmosphere.

14. The method according to claim 13, wherein the nitriding step is plasma nitriding at a temperature of 300 to 600° C., a pressure of 50 to 600 Pa, and a nitriding atmosphere for 1 to 100 hours.

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