Cutting Tool Inserts

Abstract

The present invention relates to a cutting tool insert comprising a carrier body (A) made of a maraging steel comprising at least one rake face, at least one flank face, at least one pocket and at least one cutting element (B) located in said at least one pocket. The cutting element comprises at least one cutting end (C) and can be made of any material known in the art of cutting. The cutting tool insert further comprises a braze joint joining said carrier body and said at least one cutting element, the braze joint comprising Ti, the braze joint comprising a Ti-containing bonding layer having a thickness of 0.03-5 μm adjacent to the cutting element.

Description

[Technical field]

[0001] The present invention relates to a cutting tool insert comprising a maraging steel carrier body and a cutting element, the carrier body and the cutting element being joined by brazing. The present invention also relates to a method of making such a cutting tool insert. [Background technology]

[0002] It is known in the art to weld or braze cutting elements to a carrier body of a different material than the cutting elements. One example of this is brazing cutting elements of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PcBN) to a carrier body made from cemented carbide. This is done for several reasons, polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PcBN) are more expensive than cemented carbide and are also more difficult to machine (i.e., form into the desired shape) than cemented carbide. The use of steel as the carrier material is not considered an option due to problems with brazing and low hardness and / or tensile strength of steel. Since cutting tool inserts are subjected to large forces when used in cutting operations, the brazed joints need to be strong and the carrier body needs to have an optimal toughness / hardness ratio.

[0003] Joining steel with, for example, cemented carbide, polycrystalline diamond (PCD) or cubic boron nitride (cBN) by brazing or welding has long been known in the art of tool making. Several challenges exist when joining steel with such materials, such as differences in CTE (coefficient of thermal expansion), strength of the brazed joint, and undesirable hardness profile of the steel.

[0004] Although cemented carbide seems suitable for use as a carrier body, it still has its drawbacks. For environmental reasons, recycling of cemented carbide is preferred, which is a complicated process. Also, to form the final cemented carbide carrier, separate press tools are required for each geometric shape, since the basic shape of the final cemented carbide carrier body is formed by pressing before sintering. Also, cemented carbide is difficult to process, and extensive grinding etc. is usually required to reach the final shape of the cutting tool.

[0005] One object of the present invention is to provide a cutting tool insert having a steel carrier body capable of withstanding forces during metal cutting operations.

[0006] It is another object of the present invention to provide a cutting tool insert having a cutting element joined to a steel carrier body with a high strength braze joint.

[0007] Another object of the present invention is to provide a cutting tool insert whose carrier body is easily recycled.

[0008] Another object of the present invention is to provide a cutting tool insert in which the carrier body can be formed with less effort compared to a cemented carbide carrier body.

[0009] definition By cutting tool insert is meant herein an insert used in metal cutting applications such as milling, turning, drilling, etc. The cutting tool insert comprises at least one rake face and at least one flank face, and at least one cutting edge between the rake face and the flank face.

[0010] Cutting tool inserts are usually fixed in a tool holder, for example a milling or turning holder, or may be fixed in a drill. The inserts are generally provided with a hole to facilitate fixing. The inserts are designed to be easily replaced when worn. They may also be called indexable inserts. The inserts may have any shape used in the art of cutting applications. One type of insert is shown in Figure 1.

[0011] By cutting element is meant herein the portion of the cutting tool insert which is engaged in the cutting operation, i.e. the portion which includes at least one cutting edge and which contacts the workpiece. In the art, a cutting element may also be referred to as a "cutting tip."

[0012] By carrier body is meant in this document the insert body that does not constitute the cutting element. The carrier body comprises a pocket (also called in the art as a recess, notch, seat, etc.) in which the cutting element is located. The carrier body can have any shape of a cutting tool insert, see above. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of a cutting tool insert 1 having a rake face 2, a clearance face 3 and a cutting end 4. [Diagram 2] FIG. 2 is a schematic diagram of a cutting tool insert showing the carrier body A, cutting element B and cutting end C. [Diagram 3] FIG. 2 is a schematic diagram of a cutting tool insert showing the carrier body A, cutting element B and cutting end C. [Figure 4] FIG. 1 is a schematic diagram of a cutting tool insert showing a carrier body A, a cutting element B having a cemented carbide support E and a cutting element material D including a cutting end C. [Diagram 5] FIG. 2 is a cross-sectional view of a portion of a cutting tool insert with a cutting element B attached to a carrier body A by a braze joint F. [Figure 6]1 is a cross-sectional view of a portion of a cutting tool insert with a cutting element B attached to a carrier body A by a braze joint F. The cutting element B has a cemented carbide support E and a cutting element material D. [Figure 7] FIG. 2 shows LOM (optical optical microscope) images of wear of a cemented carbide cutting element brazed to a maraging steel carrier according to the invention from Example 1. [Figure 8] FIG. 2 shows a LOM (optical optical microscope) image of the wear of the prior art solid cemented carbide insert from Example 1. [Figure 9] FIG. 13 shows an SEM (scanning electron microscope) image of the wear of a PcBN cutting element brazed to a maraging steel carrier according to the invention from Example 3. [Figure 10] FIG. 13 shows an SEM (scanning electron microscope) of the wear of a PcBN cutting element brazed to a cemented carbide carrier according to the prior art from Example 3. [Figure 11] 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 12] FIG. 2 shows an example of a hardness depth curve showing decreasing hardness values ​​from the surface to the center, where A is the average center hardness, B is the limit hardness, and C is the nitriding depth. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to a carrier body having at least one rake face, at least one clearance face, and at least one pocket; at least one cutting element located within the at least one pocket, the cutting element having at least one cutting end; a braze joint joining the carrier body and the at least one cutting element; The brazed joint comprises Ti, and the brazed joint also comprises a Ti-containing bonding layer having a thickness of 0.03-5 μm adjacent to the cutting element. The carrier body is made of maraging steel.

[0015] The cutting elements may be made from one of any material known in the art of metal cutting, i.e., cemented carbide, cermet, ceramic, polycrystalline diamond (PCD), or sintered cubic boron nitride (PcBN). The number of cutting elements brazed to the carrier body can vary depending on the specific cutting application, etc., but is typically between 1 and 8.

[0016] By ceramic is meant herein materials comprising transition metal carbide, nitride or carbonitride particles, e.g. WC, Si3N4, SiAlON, Al2O3 / SiC-wisker, etc., embedded in an oxide ceramic matrix, e.g. aluminum oxide, where the amount of transition metal carbide, nitride or carbonitride particles is 5-45% by volume. They are generally sintered in a hot isostatic pressing process.

[0017] The cemented carbide used as the cutting elements can be made from any cemented carbide known in the art. A cemented carbide comprises a hard phase embedded in a metallic binder phase matrix.

[0018] By hardmetal it is meant here that at least 50% by weight of the hard phase is WC.

[0019] Suitably, the amount of the metallic binder phase is 3-20% by weight of the hardmetal, 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.

[0020] By main component it is meant herein that no other elements are added to form the binder phase, except for those mentioned above, but if other components are added, such as Cr, it will necessarily be dissolved in the binder during sintering.

[0021] In one embodiment of the present invention, the cemented carbide may also include other components common to cemented carbides, such as elements selected from Cr, Ta, Ti, Nb, and V present as elements or as carbides, nitrides, or carbonitrides.

[0022] By cermet is meant herein a material comprising hard constituents within a metallic binder phase, the hard constituents comprising carbides or carbonitrides of one or more of Ta, Ti, Nb, Cr, Hf, V, Mo, and Zr, such as TiN, TiC, and / or TiCN.

[0023] 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 between 0.5 and 30 μm. PCD may also contain one or more elements selected from Al, Cr, Co, Ni, V, Fe, and Si.

[0024] By PcBN herein is meant a material comprising cBN particles incorporated in a metallic and / or ceramic binder, the amount of cBN particles being 30-99% by volume. The ceramic binder may include one or more components which are carbides, nitrides, carbonitrides, borides, or oxides of Co, Ni, and elements selected from Groups 4-6 of the Periodic Table of the Elements.

[0025] 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 typically produced by providing a suitable powder mixture that is subjected to a high-temperature, high-pressure (HP / HT) sintering process to form a sintered body (typically 1400°C, 5GPa).

[0026] When polycrystalline diamond (PCD) and sintered cubic boron nitride (PcBN) are provided with a cemented carbide support, 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 a powder mixture of the optimal PCD or cBN and then the cup is 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, for example using a laser or a WEDM (wire electrical discharge machining).

[0027] The hard metal used as a support for the polycrystalline diamond (PCD) and sintered cubic boron (PcBN) can be made from any hard metal common in the art, see definition above.

[0028] Maraging steels are a type of steel that hardens by precipitation of intermetallic compounds. Maraging steels suitably contain 8-25 wt.% Ni and one or more alloying elements selected from Co, Mo, Ti, Al, and Cr in a total amount of 7-27 wt.%, preferably 7-23 wt.% of the alloying elements. Maraging steels usually contain less carbon than conventional steels, suitably 0.03 wt.% or less C. The balance is Fe.

[0029] 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 8.5-12.5 wt%, Mo in an amount of 3-10 wt%, preferably 3-6 wt%, Ti in an amount of 0.1-1.6 wt%, preferably 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 less than 0.03 wt%. The balance is Fe.

[0030] In one embodiment of the present invention, the maraging steel has a composition of 17-19 wt% Ni, 8.5-12.5 wt% Co, 4-6 wt% Mo, 0.5-1.2 wt% Ti, 0-0.15 wt% Cr, 0-0.2 wt% Al, and less than 0.03 wt% C. The remainder is Fe.

[0031] In another embodiment of the invention the maraging steel has a composition of 8-11 wt% Ni, preferably 9-10 wt% Ni, 2.5-4 wt% Cr, preferably 3-3.5 wt% Cr, 3.5-5 wt% Mo, preferably 4-4.5 wt% Mo, 0.4-1.1 wt% Ti, preferably 0.7-0.9 wt% Ti, less than 0.4 wt% Si, less than 0.4 wt% Mn and the balance Fe.

[0032] Like many alloys, maraging steels may contain unavoidable impurities. By impurity is meant herein any element that may be present in the maraging steel in such small amounts 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.

[0033] In one embodiment, for 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.%.

[0034] The average hardness of maraging steel parts depends on whether an ageing / nitriding step has been performed or not, see below.

[0035] In one embodiment of the invention, the carrier body made from maraging steel is not gradient in hardness with an average hardness of 300-1200 HV1, preferably 500-1100 HV1. The standard deviation of the hardness values ​​is suitably 0-150 HV1, preferably 0-100 HV1.

[0036] In one embodiment of the present invention, the average hardness of the maraging steel part is preferably 40-55HRC, more preferably 42-55HRC. The HRC value corresponds to 390-610HV1, more preferably 400-610HV1. The standard deviation of the hardness values ​​is suitably 0-2HRC, preferably 0-1.5HRC.

[0037] In one embodiment of the invention, the carrier body made from maraging steel is provided with a hardness gradient, i.e. the carrier body has an increased hardness in the surface region compared to the center. By this it is meant herein that the hardness has its maximum value at the surface and then gradually decreases towards the center. The carrier body made from maraging steel has an average central hardness of 300-700 HV1, preferably 500-700 HV1. The standard deviation of the central hardness values ​​is suitably 0-20 HV1, preferably 0-15 HV1. The surface of the maraging steel therefore has an average surface hardness of 300-1200 HV1, preferably 500-1100 HV1. The standard deviation of the hardness values ​​is suitably 0-150 HV1, preferably 0-100 HV1. The surface hardness is at least 30% higher than the central hardness, preferably at least 40% higher than the central hardness.

[0038] By "center" herein is meant the inner portion of the maraging steel carrier body where the hardness no longer changes when measured in cross section.

[0039] The depth of the hardness gradient measured from the surface, the nitriding depth, is determined by constructing a hardness depth curve on a cross section of a maraging steel carrier provided with a hardness gradient and measuring HV0.3 or HV0.5 according to standard DIN EN ISO6507-1 starting near the surface and until the hardness stops changing towards the center. The nitriding depth is given by the vertical distance from the surface of the nitrided carrier body to the point of limit hardness, the limit hardness being defined as the average central hardness + 50HV0.3 or 50HV0.5, see figure 12.

[0040] The average nitriding hardness depth of the maraging steel carrier body is 0.001-0.8 mm, preferably 0.01-0.3 mm. The standard deviation of the hardness values ​​is suitably 0-0.03 mm, preferably 0-0.02 mm.

[0041] Increasing the hardness of the surface of the maraging steel carrier improves wear resistance, which can be of great advantage when the cutting tool insert according to the invention is used in cutting applications where chips from the workpiece material impact the maraging steel carrier.

[0042] The brazing technique is so-called active brazing. By that we mean that the joint is not formed simply by melting the filler material and forming a metallurgical bond, but also involves a chemical reaction with one or both of the materials to be joined. The joining element in the filler material is usually Ti, but elements such as Hf, V, Zr, and Cr are also considered to be active elements. According to the present invention, Ti is an active element.

[0043] By brazed joint is meant herein the area or mass between the cemented carbide and the maraging steel component that is filled by the filler material and formed during the brazing process, see below.

[0044] The thickness of the brazed joint is suitably between 5 and 200 μm, preferably between 15 and 100 μm.

[0045] The brazed joint is not a homogeneous phase. Instead, after brazing, the elements in the filler material form different alloy phases.

[0046] 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 to form a strong Ti-containing bond layer at the interface between the brazed joint and the cutting element.

[0047] The composition of the Ti-containing bonding layer varies depending on what material the cutting element is made of, but it usually consists of one or a mixture of TiC, TiN, TiOx, and TiBx. Because the bonding layer formed is ceramic in nature, the bond can become brittle if the layer growth is not controlled.

[0048] For example, if the material closest to the braze joint is PCD (polycrystalline diamond) or cemented carbide, the entire cutting element is made from cemented carbide, or it is a carbide-backed PCD or PcBN cutting element, the Ti-containing bond layer is a TiC layer. The Ti in the braze joint reacts with the carbon in the WC or diamond to form TiC.

[0049] Another example is when the cutting element is made from solid (also called "free-standing") PcBN, the bonding layer will be TiN as Ti reacts with the nitrogen in the PcBN, but with a small amount of TiB, e.g. TiB2. x It may also contain

[0050] 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.

[0051] There are several ways to detect the presence of a bond layer, depending on the type of equipment used.

[0052] If a scanning electron microscope (SEM) with sufficiently high resolution is used, the bond layer is clearly visible adjacent to the cut elements. To verify the composition of the layer, 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 bond layer.

[0053] 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.

[0054] If the SEM images used do not have sufficient resolution to detect the bond layer, the accumulation of Ti and / or C at the interface between the fill material and the cutting element can be seen, for example, using SEM-EDS or SEM-EPMA with WDS. The accumulation of Ti, later referred to as the Ti accumulation layer, is one indicator that a bond layer has formed, even if it is not visually detectable in the SEM images. The Ti accumulation layer is much thicker than the actual bond layer, since all the Ti is in the TiC / TiN / TiO x This may mean that Ti does not form TiBx / TiBx. The thickness of the Ti accumulation layer is also partly influenced by the analytical method.

[0055] 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 Ag, Cu and In.

[0056] The brazed joint may also contain smaller 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. When the temperature increases during the brazing process, small amounts of elements from the parts being joined will inevitably dissolve into the brazing material, thereby melting the brazing material and allowing diffusion out of the joint. As long as the brazing process parameters, such as temperature and time, are within the scope of the present invention, the total amount of unavoidable impurities is small enough not to affect the performance of the brazed joint.

[0057] The composition of the brazed joint after brazing is difficult to determine because the elements are not uniformly distributed. If available, the easiest way is to look at the filler material used, as the paste or foil is a homogenous blend. Also, the brazed joint may contain small amounts of elements from the materials being joined, e.g. Co, W from cemented carbide, and Fe, Ni from maraging steels.

[0058] 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 the precipitated elements in the brazed joint, many measurement points need to be used, leading to 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.%, more preferably 20-40 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.%, more preferably 10-25 wt.%.

[0059] 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 accumulated layer of Ti at the maraging steel surface is preferably 1-10 μm, preferably 2-5 μm, and can be measured, for example, by EDS.

[0060] The present invention also provides providing a maraging steel carrier body having at least one pocket; providing at least one cutting element disposed within the at least one pocket; disposing a filler material in contact between the maraging steel 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 maraging steel carrier body and the cutting element with the filler material therebetween to a brazing process in a furnace at a temperature of 600-780° C. for a time period of 1-60 minutes, the brazing being carried out in a vacuum; The present invention also relates to a method of making a cutting tool insert according to the above, comprising:

[0061] The fill material (also called braze metal) according to the present invention contains Ti in a total amount of 0.3-15% by weight of the fill material, preferably 1-5% by weight. The fill material of the present invention suitably has a solidus temperature of 490-1125°C, preferably 600-700°C. Furthermore, the fill material of the present invention has a liquidus temperature of 610-1180°C, preferably 700-750°C. In addition to Ti, the fill material further comprises one or more elements selected from Ag, Cu, Sn, In, Zr, Hf and Cr.

[0062] 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%, more preferably 20-40 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%, more preferably 10-25 wt%.

[0063] Suitably the filler material is provided as a foil or a paste.

[0064] A filler material is provided at the faying surfaces of the cemented carbide substrate and the steel component.

[0065] The thickness of the filler material provided to the joining surfaces prior to the brazing process depends on the type of material, i.e. 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 5-200 μm, preferably 15-100 μm.

[0066] The parts are then placed in a furnace with an inert or reducing environment, i.e. with a minimum amount of oxygen. Preferably, the brazing temperature in the furnace is 600-830°C, preferably 600-780°C, more preferably 650-750°C, even more preferably 700-750°C. The time that the parts are subjected to the high temperature is 1-60 minutes, preferably 5-15 minutes. If the time at high temperature is short, the brazed joint is formed and there is not enough time for the Ti to react and reach the desired strength of the brazed joint. If the time at high temperature is long, the Ti-containing brittle reaction zone grows in an uncontrolled manner, adversely affecting the joint properties, e.g., shear strength.

[0067] Brazing is suitably carried out in a vacuum or in the presence of argon at low partial pressure, which is defined herein 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 Less than mbar.

[0068] The brazing furnace used in accordance with the present invention can be any furnace capable of providing well-controlled conditions with respect to vacuum, heating and cooling rates, etc., as described above.

[0069] In one embodiment of the invention the parts are subjected to an ageing step after brazing by subjecting the brazed parts to a high temperature ageing 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 to 6 hours. Suitably the heating rate to the ageing temperature is preferably 1-50°C / min, preferably 5-10°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 1-50°C / min, preferably 5-10°C / min. The brazing and ageing steps can be carried out either in the same furnace or in two separate furnaces.

[0070] In one embodiment of the present invention, aging occurs immediately after the brazing step in the same furnace in which the brazing step occurs.

[0071] In one embodiment of the present invention, aging occurs immediately after the brazing process in a furnace separate from the vacuum brazing.

[0072] In one embodiment of the present invention, aging is performed in the same furnace / deposition chamber prior to or during deposition of the coating.

[0073] In one embodiment of the 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 carried out, there is usually no further separate aging step.

[0074] 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.

[0075] In one embodiment of the present invention, the nitriding step is carried out using plasma nitriding. Thereby, 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. In case of plasma nitriding, the gas is preferably N2, which may be mixed with, for example, H2.

[0076] In one embodiment of the present invention, the nitriding step is carried out using gas nitriding. Gas nitriding is preferably carried out at a temperature of 450-600°C, preferably 500-520°C. Gas nitriding is preferably carried out with NH3, which is split into H2 and N2 in the reactor. Gas nitriding can be carried out at low pressure, preferably 0.05-0.02 MPa, or close to atmospheric pressure.

[0077] The exact temperature, duration, and selection of nitriding gas will depend on several things, such as the desired nitriding effect on the maraging steel, the specific type of equipment being used, etc.

[0078] In one embodiment of the present invention, the maraging steel part has the following composition by weight: 18-19% Ni, 8-10% Co, 4-6% Mo, 0.5-1.2% Ti, 0-0.15% Cr, 0-0.2% Al, less than 0.03% C, less than 0.04% Si, less than 0.05% Mn, less than 0.003% P, less than 0.002% S, and less than 0.0005% B. The balance is Fe. The filler material has the following composition by weight: Ag in an amount of 40-75%, Cu in an amount of 15-40%, Ti in an amount of 0.5-5%, Sn in an amount of 0-2%, and In in an amount of 5-25%.

[0079] 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 has the following composition by weight: 40-75% Ag, 15-40% Cu, 0.5-5% Ti, 0-2% Sn, and 5-25% In. EXAMPLES

[0080] [Example 1] The maraging steel carrier body of insert type CNMG120408 was made from maraging steel Bohler W720 VMR with the composition: 18.46 wt% Ni, 8.71 wt% Co, 5.00 wt% Mo, 0.68 wt% Ti, 0.09 wt% Cr, <0.0005 wt% S, <0.0030 wt% P, <0.02 wt% Mn, <0.020 wt% Si, <0.0010 wt% C, <0.06 wt% Al, and <0.0005 wt% B. The pocket was created by cutting out a piece of maraging steel at one of the corners using a milling cutter.

[0081] Cemented carbide cutting elements were given the same shape as the pockets. The cemented carbide had a composition of 6 wt% Co and the remainder WC. The cutting elements were cut using wire electrical discharge machining (WEDM) of solid cemented carbide inserts of the same type as the inserts used in the comparison (Comparative 1, see below).

[0082] The fill material was provided in the form of a paste (TB-629) manufactured by Tokyo Braze, having a composition of 58-62 wt% Ag, 22-26 wt% Cu, 1.5-2.5 wt% Ti, and 13-15 wt% In. The solidus temperature is about 620°C and the liquidus temperature is about 720°C.

[0083] The paste was placed between the maraging steel carrier body and the cemented carbide cutting element so that both pieces were in contact with the paste. The assembled joint pieces were then placed in an Ipsen VFC-124 vacuum furnace where the temperature was first raised to 500°C at a rate of 10°C / min to allow evaporation of the binder in the filler material and held there for 20 minutes to allow a uniform insert temperature. The pieces were then heated to 740°C at a rate of 10°C / min. The brazing temperature of 740°C was maintained for 10 minutes after which the pieces were cooled to 300°C at a rate of 5°C / min. After 300°C the pieces were free to cool.

[0084] After the brazing process, the brazed pieces were subjected to an ageing process to increase the hardness of the maraging steel. The pieces were placed in the same furnace as the brazing, where the temperature was raised to the ageing temperature at a rate of 5°C / min. The ageing temperature of 410°C was maintained for 4 hours, after which the pieces were cooled to 200°C at a rate of 5°C / min. After 200°C the pieces were allowed to cool freely.

[0085] The insert is designated Invention 1 herein.

[0086] For comparison, an insert having the same shape as Invention 1 but without the steel carrier, i.e. the entire insert was made from a cemented carbide of the same composition as the cutting element of Invention 1. This insert is referred to herein as Comparative 1.

[0087] The inserts were tested in longitudinal turning of Ti6Al4V with the following cutting parameters: V c =50~100m / min a p =1~2mm f=0.2mm / revolution Wet conditions

[0088] The hardness of the maraging steels after aging displayed in Table 1 was measured as HRC on a Rockwell indentation device, a Wolpert Testo 2000. The average value is the average of at least three measurement points.

[0089] The results of flank wear (VB) in mm for various cutting parameters are shown in Table 1. [Table 1] TIFF2024544525000002.tif35170

[0090] In Table 1, it can be seen that for various cutting parameters, the wear is almost the same for both Inventive 1 and Comparative 1. Thus, the maraging steel carrier body shows the same performance as the cemented carbide tool.

[0091] No deformation of the maraging steel carrier was observed. After the cutting test, the brazed joint was unaffected by visual inspection. In FIG. 7, the LOM (optical microscope) of the wear of the cutting element of Inventive 1 is shown in comparison with the LOM (optical microscope) shown in FIG. 8 of the wear of Comparative 1, both images show that the wear of the cutting element of Inventive 1 is significantly different from that of Comparative 1. c =100m / min, a p = 2 mm, f = 0.2 mm / revolution, and T = 4 min.

[0092] [Example 2] The maraging steel carrier body of the insert type CNMG120408 was made from maraging steel Bohler W720 VMR. The pocket was created by cutting out a piece of maraging steel at one of the corners using EDM.

[0093] The cutting element (tip) of PCD on a cemented carbide support, i.e. carbide back, was given the same shape as the pocket. The PCD had a composition of 96% diamond by volume and the remainder Co with an average grain size of 6um.

[0094] The cutting tip was brazed using the same filler material and process as in Example 1. The insert was also aged using the same conditions as in Example 1.

[0095] The insert is designated as Invention 2 herein.

[0096] For comparison, a carrier body was provided having the same shape (including the pocket) as Invention 2, but made from cemented carbide. A cutting element having the same composition as Invention 2 was brazed to the cemented carbide carrier body using the same filler material and process (except for the aging step) as Invention 2. This insert is referred to herein as Comparative 2.

[0097] Both inserts (Inventive 2 and Comparative 2) were ground after brazing and the cut ends were brushed to form an ER of 20 um.

[0098] The inserts were tested in a turning cutting operation in Ti6Al4V with the following cutting parameters: V c =150m / min a p =0.5mm f=0.12mm / revolution Wet conditions

[0099] Both inserts according to Inventive 2 and Comparative 2 were evaluated after 18 minutes and the results of flank wear (VB) in mm are shown in Table 2. [Table 2] TIFF2024544525000003.tif18170

[0100] In Table 2, it can be seen that the wear is almost the same for both Inventive 2 and Comparative 2. Thus, the maraging steel carrier body performs the same as the cemented carbide carrier.

[0101] No deformation of the maraging steel carrier was observed. After the cutting test, the brazed joint was unaffected by visual inspection.

[0102] [Example 3] The maraging steel carrier body of the insert type CNMG120408 was made from maraging steel Bohler W720 VMR. The pocket was created by cutting out a piece of maraging steel at one of the corners using a milling cutter.

[0103] A cutting element (tip) of cBN (free-standing, i.e. without a cemented carbide support) was given the same shape as the pocket. The cBN had a composition of 65% by volume of cBN balanced with TiCN as the binder phase and unavoidable impurities.

[0104] The cutting tip was brazed using the same filler material and process as in Example 1, but now brazed at 720° C. The insert was also aged using the same conditions as in Example 1, but now at 420° C. for 3 hours.

[0105] The insert is designated herein as Invention 3.

[0106] For comparison, a carrier body was provided having the same shape (including the pocket) as Invention 3, but made from cemented carbide. A cutting element having the same composition as Invention 3 was brazed to the cemented carbide carrier body using the same filler material and process (except for the aging step) as Invention 3. This insert is referred to herein as Comparative 3.

[0107] Both inserts (Inventive 3 and Comparative 3) were ground after brazing and the cut ends were brushed to form an ER of 20 um.

[0108] The inserts were tested in a facing turning operation in the case of hardened steel Ovako 16NiCrS4 with the following cutting parameters: V c =180m / min a p =0.1mm f=0.1mm / revolution Drying conditions

[0109] In one test, inserts according to Inventive 3 and Comparative 3 were evaluated after 2.5 minutes, and in an additional test, two inserts of each type, Inventive 3 and Comparative 3, were evaluated after 30 minutes. In both tests, the flank wear (VB B ) and notch wear (VB C ) were evaluated. The results are shown in Table 3. Results from the 30-minute test are the average of two tests. [Table 3] TIFF2024544525000004.tif23170

[0110] In Table 3, it can be seen that the wear is almost the same for both Inventive 3 and Comparative 3. Thus, the maraging steel carrier body performs the same as the cemented carbide carrier.

[0111] No deformation of the maraging steel carrier was observed. After the cutting test, the brazed joint was unaffected by visual inspection. In FIG. 9, a SEM (Scanning Electron Microscope) image of the wear of the cutting element of Inventive 3 is shown in comparison with the SEM (Scanning Electron Microscope) image shown in FIG. 10 of the wear of Comparative 3, both images taken after 30 minutes.

[0112] [Example 4] The maraging steel carrier body of the insert type CNMG120408 was made from maraging steel Bohler W720 VMR. The pocket was created by cutting out a piece of maraging steel at one of the corners using EDM.

[0113] A ceramic cutting element (tip) (free-standing, i.e., without a cemented carbide support) was given the same geometry as the pocket. The ceramic tip had a composition of 30% by volume WC, balanced with Al2O3 and unavoidable impurities.

[0114] The cutting tip was brazed using the same filler material and process as in Example 1. The insert was also aged using the same conditions as in Example 1.

[0115] The insert is designated herein as Invention 4.

[0116] For comparison, a carrier body was provided having the same shape (including the pocket) as Invention 4, but made from cemented carbide. A cutting element having the same composition as Invention 4 was brazed to the cemented carbide carrier body using the same filler material and process (except for the aging step) as Invention 4. This insert is referred to herein as Comparative 4.

[0117] Both inserts (Inventive 4 and Comparative 4) were ground after brazing and the cut ends were brushed to form an ER of 20 um.

[0118] The inserts were tested in a facing turning operation in the case of hardened steel Ovako 16NiCrS4 with the following cutting parameters: V c =180m / min a p =0.1mm f=0.1mm / revolution Drying conditions

[0119] Both inserts according to Inventive 4 and Comparative 4 were evaluated after 2.5, 4.5 and 13.5 minutes and the flank wear in μm (VB max ) results are shown in Table 4. [Table 4] TIFF2024544525000005.tif18170

[0120] In Table 4, it can be seen that the wear is almost the same for both Inventive 4 and Comparative 4. Thus, the maraging steel carrier body performs the same as the cemented carbide carrier.

[0121] No deformation of the maraging steel carrier was observed. After the cutting test, the brazed joint was unaffected by visual inspection.

[0122] [Example 5] A steel part made from maraging steel 1.2709 in the form of a cylinder was provided together with a cemented carbide part having a composition of 10 wt.% Co, 1 wt.% other carbides, and the remainder WC. The maraging steel had a hardness of about 340 HV1 prior to brazing.

[0123] The brazing material (Incusil ABA from WBC Group) was provided in the form of a foil having a thickness of 100 μm. 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.

[0124] The 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 30x45x30 6 bar system *2RV*), where the temperature was first raised to 740°C at a rate of 20°C / min. The brazing temperature of 740°C was held for 15 minutes, after which the pieces were cooled to 300°C at a rate of 5°C / min. After 300°C the pieces were free to cool to room temperature.

[0125] Excellent wetting with no signs of thermal stress cracking could be observed and was evidenced by the high shear test results.

[0126] This sample is designated as Invention 5 herein.

[0127] [Example 6] A steel part made from maraging steel 1.2709 in the form of a cylinder was provided together with a cemented carbide part having a composition of 10 wt.% Co, 1 wt.% other carbides, and the remainder WC. The maraging steel had a hardness of about 340 HV1 prior to brazing.

[0128] The brazing material (TB-651 from Tokyo Braze) was provided in the form of a foil having a thickness of 100 μm. The brazing material had 65.0 wt.% Ag, 28.0 wt.% Cu, 2.0 wt.% Ti, and 5.0 wt.% Sn. The solidus temperature was about 700° C. and the liquidus temperature was about 750° C.

[0129] The 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 30x45x30 6 bar system *2RV*), where the temperature was first raised to 815°C at a rate of 20°C / min. The brazing temperature of 815°C was held for 15 minutes, after which the pieces were cooled to 300°C at a rate of 5°C / min. After 300°C the pieces were free to cool.

[0130] Excellent wetting with no signs of thermal stress cracking could be observed and was evidenced by the high shear test results.

[0131] This sample is designated as Invention 6 herein.

[0132] [Example 7] (Plasma nitriding) The samples according to inventions 5 and 6 were subjected to a plasma nitriding process in a gas flow of H2:N2 of 350:50 ml / min at a chamber pressure of 3 mbar. The temperature in the chamber was 490° C. The time the samples were subjected to the plasma nitriding process was 16 hours. No masking of the brazed joints was used prior to nitriding.

[0133] [Example 8] (Gas nitriding) The samples according to invention 1 were subjected to a gas nitriding process by NH3 splitting. The temperature in the chamber was 510°C. The time the samples were subjected to the plasma nitriding process was 23 or 55 hours. No masking of the brazed joints was used prior to nitriding.

[0134] [Example 9] The samples were analyzed for shear strength, surface hardness, center hardness, and hardness depth curve.

[0135] The shear strength was analyzed by the setup of the shearing apparatus shown in Figure 11, where 1 is a steel part in the form of a steel cylinder (φ = 20 mm, h = 5 mm) and 2 is a cemented carbide part in the form of a cemented carbide cylinder (φ = 10 mm, h = 5 mm). The steel cylinder is placed in the gap of the shear strength test apparatus, so that it can only move in the loading direction. The notches formed on the surface of the apparatus hold the joined parts in the correct position and ensure the induction of an evenly distributed force to the brazed joint. The applied force F was constantly increased until the brazed joint failed and the cemented carbide cylinder was sheared off. The final shear strength was then calculated as the function of the maximum measured force and the initial joint area (A = 78, 5 mm 2The brazing material was not removed prior to determining the shear strength of the brazed joint.

[0136] To determine the depth of nitriding for the samples prepared according to Example 7, the average nitriding hardness depth was determined at room temperature. This was done by creating a hardness depth curve on the cross section of the nitrided sample according to standard DIN EN ISO6507-1, starting from the first indentation 0.025-0.1 mm from the edge, and then measuring HV0.3 every 0.03-0.10 mm until the hardness no longer changes. The obtained hardness values ​​are recorded as a function of the distance from the surface. From this hardness curve, the nitriding hardness depth was obtained as the distance between the surface and the limit hardness (where the limit hardness is the average central hardness (in HV0.3 units) + 50 HV0.3). For the samples prepared according to Example 8, the nitriding depth was determined in the same way as for the samples of Example 7, with the difference that HV0.5 was used.

[0137] The central hardness given in Table 5 is HV1 and is measured by Vickers hardness tester on cross sections of maraging steel parts using a load of 1 kgf (kilogram force) and a loading time of 15 seconds.

[0138] A pattern of five dimples spaced 1.5 mm apart was performed according to the standard and the values ​​given in Table 5 are the average of the five dimples.

[0139] Surface hardness measurements were performed on the nitrided surfaces, with at least five indentations spaced 1.5 mm apart, and the values ​​given 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 load time of 15 seconds. [Table 5] TIFF2024544525000006.tif45170

[0140] As can be seen from Table 1, nitriding creates a surface that is significantly harder than the center, which translates into improved wear resistance.

Claims

1. a carrier body having at least one rake face, at least one flank face, and at least one pocket; at least one cutting element located within the at least one pocket, the cutting element including at least one cutting end; 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 having a thickness of 0.03 to 5 μm adjacent the cutting element; Equipped with The carrier body is made of maraging steel. Cutting tool inserts.

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

3. The composition of the Ti-containing bonding layer is TiC, TiN, TiO ｘ , and TiB ｘ 10. The cutting tool insert of claim 1, wherein the insert is one of:

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

5. 2. The cutting tool insert according to claim 1, wherein the maraging steel comprises 11-25 wt% Ni, 7-15 wt% Co, 3-10 wt% Mo, 0.1-1.6 wt% Ti, 0-0.15 wt% Cr, 0-0.2 wt% Al, less than 0.03 wt% C, and the remainder being Fe and impurities.

6. 2. The cutting tool insert according to claim 1, wherein the maraging steel comprises 15-25 wt% Ni, 8.5-12.5 wt% Co, 3-6 wt% Mo, 0.5-1.2 wt% Ti, 0-0.15 wt% Cr, 0-0.2 wt% Al, less than 0.03 wt% C, and the balance being Fe and impurities.

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

8. The cutting tool insert according to claim 1, wherein said carrier body of maraging steel has an average center hardness of 300 to 700 HV1 and an average surface hardness of 300 to 1200 HV1.

9. 9. The cutting tool insert of claim 8, wherein the carrier body of maraging steel is provided with a hardness profile such that the surface hardness is at least 30% higher than the center hardness.

10. A method of making a cutting tool insert according to any one of claims 1 to 9, comprising the steps of: Providing a carrier body made of maraging steel having at least one rake face, at least one flank face, and at least one pocket; providing at least one cutting element including at least one cutting end; providing a maraging steel component; disposing a filler material between and in contact with 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 period of 1-60 minutes, wherein the brazing is carried out in a vacuum; A method comprising:

11. The method of claim 10, wherein the brazing is carried out at a temperature of 650-750°C for a time period of 5-15 minutes.

12. The method of claim 10, wherein the carrier body and the cutting element with the filling material therebetween are subjected to an ageing step at a temperature of 300-600° C. for a period of 5 minutes to 12 hours.

13. 13. The method of claim 12, wherein the aging step is carried out at a temperature of 350-500°C for a period of 30 minutes to 8 hours.

14. The method according to claim 10, wherein after the brazing step, the carrier body and the cutting element are subjected to a nitriding step at a temperature of 300-600° C. in a nitriding atmosphere.

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

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