How to make tools

Abstract

The present invention relates to a method for making a tool, comprising joining a maraging steel joining partner (1) and a cemented carbide joining partner (2) by brazing. The present invention also relates to a tool made according to this method. The method comprises depositing a Ni coating on the maraging steel part before applying a filler material comprising at least 70 wt. % Cu. The brazed joint exhibits excellent shear strength.

Description

[Technical field]

[0001] The present invention relates to a method of making a tool, comprising joining a maraging steel joining partner and a cemented carbide joining partner by brazing. The present invention also relates to a tool made according to this method. [Background technology]

[0002] Joining steel with cemented carbide by brazing or welding has long been known in the art of making tools. There are several challenges when joining steel with cemented carbide, such as differences in CTE (coefficient of thermal expansion), strength of the brazed joint, and undesirable hardness profile of the steel.

[0003] There are some solutions that can improve each of these problems individually, but those solutions often create problems in other areas, and not all problems can be solved.

[0004] The principle of brazing is the use of a filler material that when heated will join two pieces together. There are several ways to heat the brazed joint, one of the most common is induction heating using an induction coil. One of the advantages of using a coil is that only the localized area around the brazed joint is heated, while the rest of the tool remains unaffected. However, this localized heating can result in an undesirable hardness profile in the steel part, which can cause problems when the steel part is subjected to thread cutting for fastening rotating tools and other cutting tools, etc.

[0005] One object of the present invention is to provide a tool having both a solid brazed joint and steel parts with a uniform hardness profile and high hardness and therefore improved wear resistance.

[0006] Another object of the present invention is to provide a process for joining steel and hard metals that is easy to use and results in predictable joints with high strength and steel parts with predictable hardness. Summary of the Invention

[0007] The present invention relates to a method for making a tool by joining a cemented carbide joining partner with a maraging steel joining partner, the method comprising the steps of: Applying a Ni coating having a thickness between 0.5 μm and 15 μm on the faying surface of the maraging steel faying partner; placing a filler material comprising at least 70 wt. % Cu in contact with the faying surfaces of the cemented carbide faying partner and the maraging steel faying partner; exposing the cemented carbide joining partners and the maraging joining partners with the filler material therebetween to high temperatures in a vacuum furnace at a temperature between 900°C and 1200°C for a time period between 1 minute and 60 minutes; subjecting the joined cemented carbide joining partners and the maraging joining partner to a tempering process at a temperature between 300°C and 600°C for a period of 5 minutes to 12 hours; Includes.

[0008] Maraging steels are a type of steel that is hardened by the precipitation of intermetallic compounds. Maraging steels preferably contain 8-25 wt.% Ni and one or more alloying elements selected from Co, Mo, Ti, Al and Cr in a total amount of alloying elements between 7 wt.% and 27 wt.%, preferably between 7 wt.% and 23 wt.%. Maraging steels typically contain less carbon than conventional steels, preferably 0.03 wt.% or less. The balance is Fe and impurities.

[0009] In one embodiment of the present invention, the maraging steel according to the present invention 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% Co, Mo in an amount of 3-10 wt%, preferably 3-6 wt% Mo, Ti in an amount of 0.1-1.6 wt%, preferably 0.5-1.2 wt% Ti, 0-0.15 wt% Cr, Al in an amount of 0-0.2 wt%, and less than 0.03 wt% C. The balance are Fe and impurities.

[0010] 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 balance is Fe and impurities.

[0011] 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.

[0012] 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 the amount of S is less than 0.002 wt%.

[0013] The Ni coating may be deposited using any coating technique known in the art for depositing Ni coatings, such as galvanizing or PVD. The thickness of the Ni coating is between 0.5 μm and 20 μm, preferably between 2 μm and 10 μm.

[0014] In one embodiment of the present invention, the Ni coating is deposited using PVD, which includes first cleaning the steel surface by ion etching before depositing the Ni coating. The exact process parameters should be determined by one skilled in the art depending on what type of deposition equipment is to be used.

[0015] The cemented carbide bond partners may be made from any cemented carbide common in the art. Cemented carbide includes a hard phase embedded in a metallic binder phase matrix.

[0016] By hardmetal is meant in this specification that at least 50% by weight, preferably at least 70% by weight, of the hard phase is WC.

[0017] Suitably, the amount of metallic binder phase is between 3% and 20% by weight of the cemented carbide, preferably between 4% and 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.

[0018] By main component it is meant here that no other elements are added to form a binder phase, but if other components, such as Cr, are added, they will necessarily be dissolved in the binder during sintering.

[0019] In one embodiment of the present invention, the cemented carbide may also contain other constituents common to the cemented carbide elements selected from Cr, Ta, Ti, Nb and V present as elements or as carbides, nitrides or carbonitrides.

[0020] The filler material (sometimes called brazing material) according to the invention contains at least 70% by weight Cu, preferably at least 80% by weight Cu, the remaining elements can be, for example, Ge, Mn, Ni, Sn, Ag to adjust the melting temperature and wettability towards the materials to be joined.

[0021] In one embodiment of the present invention, the filler is at least 99% Cu by weight.

[0022] Preferably the filler is provided as a foil or wire.

[0023] The filler material is provided on the faying surfaces of the cemented carbide substrate and the steel component.

[0024] The thickness of the filler before the brazing process depends on the type of material, i.e. foil or wire. Typically, the thickness of the foil is between 5 μm and 200 μm, preferably between 15 μm and 100 μm.

[0025] The cemented carbide joining partner and the maraging joining partner with the filler material between them are then exposed to high temperature by placing the parts 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 between 900°C and 1200°C, preferably between 950°C and 1170°C, more preferably between 1000°C and 1150°C. The time during which the parts are exposed to the high temperature is between 1 and 60 minutes, preferably between 5 and 30 minutes. If the time at high temperature is shorter, the brazing joint does not have enough time to form and the desired strength of the brazing joint is not reached. If the time at high temperature is longer, this may have a negative effect on the steel properties.

[0026] Suitably the cooling rate from the brazing temperature to a temperature at least below the solidus temperature of the filler material, preferably below 300°C, is between 1°C / min and 50°C / min, preferably between 3°C / min and 10°C / min.

[0027] Brazing is preferably carried out in a vacuum or in the presence of argon at low partial pressure, where vacuum means a pressure in the furnace 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.

[0028] After brazing, the parts undergo an ageing step by subjecting the parts to an elevated ageing temperature between 300°C and 600°C, preferably between 400°C and 600°C, and most preferably between 500°C and 600°C, for a time between 5 minutes and 12 hours, preferably between 2 hours and 5 hours.

[0029] Preferably, the heating rate to the ageing temperature is between 1° C. / min and 50° C. / min, preferably between 5° C. / min and 10° C. / min. Preferably, the cooling rate from the ageing temperature to a temperature preferably below 300° C. is between 1° C. / min and 50° C. / min, preferably between 5° C. / min and 10° C. / min.

[0030] The brazing furnace used in accordance with the present invention can be any furnace capable of providing appropriately controlled conditions with respect to vacuum, heating and cooling rates, etc., as explained above. The brazing and ageing steps can be carried out either in the same furnace, or in two separate furnaces.

[0031] In one embodiment of the present invention, the aging treatment is carried out immediately after the brazing step in the same furnace in which the brazing step is carried out.

[0032] In one embodiment of the present invention, the aging treatment is carried out immediately after the brazing process in a furnace separate from the vacuum brazing.

[0033] In one embodiment of the present invention, the aging treatment is carried out in the same furnace / deposition chamber prior to or during the deposition of the coating.

[0034] The tool can be any tool or part of a tool common in the art where a cemented carbide part is joined to a steel part by brazing. Examples are drills, end mills, tool holders such as shanks, etc.

[0035] In one embodiment of the present invention, the tool is a shank used as a tool holder for cutting tools such as inserts, drill heads, etc. The shank is formed by a cemented carbide part and a steel part, the cemented carbide part is used to create stability and the steel part is needed to create the threading for fastening the cutting tool.

[0036] The invention also relates to a tool made according to the above method, the tool comprising a maraging steel join partner and a cemented carbide join partner and a brazed joint joining said join partners.

[0037] By braze joint is meant herein the area or mass between the cemented carbide joining partner and the maraging steel joining partner that is filled by the filler material and formed during the brazing process.

[0038] The thickness of the brazed joint is suitably between 5 μm and 200 μm, preferably between 15 μm and 100 μm.

[0039] The brazed joint has a shear strength of at least 200 MPa, preferably at least 250 MPa.

[0040] Brazed joints contain Cu and most likely some Ni. The Ni coating is very difficult to detect after the brazing process. As maraging steel joints also contain significant amounts of Ni, it is not possible to determine where the detected Ni comes from. However, the effect of the Ni coating is evident when the shear strength of the brazed joints is measured.

[0041] The average hardness of the maraging steel parts is suitably between 350HV1 and 600HV1, preferably between 400HV1 and 460HV1, more preferably between 410HV1 and 450HV1. The hardness is measured by a Vickers hardness tester, applying a load of 1 kgf (kilogram force) and a load time of 15 seconds. A 3x6 indentation pattern was applied in the entire material (not the surface) of the maraging steel parts. The average value is the average of these measurement points. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a schematic diagram of a shear testing device, where 1 is a steel joint member and 2 is a cemented carbide joint member. [Diagram 2] FIG. 1 shows SEM images of brazed joints according to the invention, where a Ni coating was deposited on the steel joining partners before brazing, where A is the cemented carbide joining member, B is the brazed joint and C is the maraging steel joining member. [Diagram 3] FIG. 1 shows SEM images of brazed joints according to the prior art, where A is the cemented carbide joint, B is the brazed joint, and C is the maraging steel joint, where no Ni coating was deposited on the steel joint partners before brazing. EXAMPLES

[0043] [Example 1] A steel part made from maraging steel 1.2709 in the form of a cylinder was prepared together with a cemented carbide part with a composition of 10 wt.% Co, 1 wt.% other carbides and the remainder WC. The maraging steel had a hardness of about 340 HV1 before brazing.

[0044] A Ni coating was deposited on a portion of the maraging steel part using arc PVD (physical vapor deposition). The sample was first ion etched (100 A, 1,000 V bias voltage, 3 Ah), and then the Ni coating was deposited using 90 A, 30 V bias voltage and 90 Ah until a thickness of 5 μm was reached.

[0045] The filler was prepared in the form of a foil having a thickness of 100 μm. The composition of the filler was 100% Cu.

[0046] The foil was placed between the maraging steel and cemented carbide parts so that both pieces were in contact with the foil. The combined joint pieces were then placed in a Schmetz vacuum furnace and the temperature was first increased to 650°C at a rate of 20°C / min, where the joint pieces were held for 10 minutes. The pieces were then heated to 850°C at a rate of 20°C / min, where they were held for 10 minutes. The temperature was then increased to the brazing temperature of 1100°C at a rate of 5°C / min. After the brazing temperature of 1100°C was held for 15 minutes, the pieces were cooled to 300°C at a rate of 5°C / min. After 300°C there was free cooling.

[0047] After the brazing process, the brazed pieces underwent an ageing process to increase the hardness of the maraging steel. The pieces were placed in the same furnace as the brazing and the temperature was increased at a rate of 5°C / min to the ageing temperature. After the ageing temperature of 580°C was maintained for 3 hours, the pieces were cooled at a rate of 5°C / min to 300°C. After 300°C there was free cooling.

[0048] In this specification, the joined pieces in which the maraging steel is Ni-coated are referred to as Invention 1, and the joined pieces in which the maraging steel is not Ni-coated are referred to as Comparative Example 1.

[0049] An SEM image of the brazed joint of Invention 1 is shown in Figure 2, and an SEM image of the brazed joint of Comparative Example 1 is shown in Figure 3. As can be seen in Figure 3, the brazed joint contains some irregularities and defects closest to the steel parts.

[0050] Excellent wetting can be observed with no signs of thermal stress cracking as evidenced by high shear test results.

[0051] [Example 2] (Comparative Example) Steel parts made from carbon hardened hot work steel 1.2344 were prepared along with cemented carbide parts with a composition of 10 wt% Co, 1 wt% other carbides and the balance WC.

[0052] The filler was prepared in the form of a foil having a thickness of 100 μm. The brazing metal had a composition of 100.0% Cu by weight. The melting temperature was 1085° C.

[0053] A foil was placed between the maraging steel and cemented carbide parts, and the combined 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 minutes. From 650°C, the temperature was then increased to the brazing temperature T Brazing The brazing temperature T Brazing The temperature was 1100°C. Brazing The temperature was maintained for a dwell time of 15 min, after which the pieces were cooled to 850 °C at a cooling rate of 50 K / min. From 850 °C, the specimens were placed under an overpressure of 2 bar and cooled for 2500 min. -1 N at fan frequency 2 The mixture was quenched by

[0054] The cemented carbide-steel joints with carbon-hardened hot-work steel 1.2344 were subsequently aged twice at 630°C for 2 h.

[0055] The sample is designated herein as Comparative Example 2.

[0056] [Example 3] The joined pieces were evaluated by measuring the shear strength of the brazed joints and the hardness of the maraging steel parts and the brazed joints were investigated for cracks etc. To assess the joint strength properties, the samples were shear tested using a shear device set up as shown in Figure 1, where 1 is the steel part in the form of a steel cylinder (φ=20 mm, h=5 mm) and 2 is the 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 device and can only move in the direction of loading. Notches eroded into the surface of the device hold the joined parts in the correct position and ensure the induction of a uniformly distributed force into the brazed joint. The applied force was constantly increased until the brazed joint failed and the cemented carbide cylinder was sheared off. The maximum measured force and the initial joint surface (A=78,5 mm) were then compared. 2 The ultimate shear strength was calculated by the quotient of the shear strength of the brazed joint and the filler material was not removed before the determination of the brazed joint shear strength. The same method was applied when testing the rods.

[0057] The hardness of the steel parts was measured by a Vickers hardness tester on the cross-section of the maraging steel parts, applying a load of 1 kgf (kilogram force) and a load time of 15 seconds. 2 A 3x6 notch pattern was applied covering the 3x6 square slab. Table 1 TIFF2024531960000002.tif24170

Claims

1. A method for manufacturing a tool by joining a cemented carbide mating member to a maraging steel mating member, comprising: applying a Ni coating having a thickness between 0.5 μm and 15 μm onto the joint surface of the maraging steel mating member; placing a filler containing at least 70 wt% Cu in contact with the joint surfaces of the cemented carbide mating member and the maraging steel mating member; subjecting the cemented carbide mating member and the maraging steel mating member with the filler therebetween to a high-temperature brazing process in a vacuum furnace at a temperature between 900°C and 1200°C for a time between 1 minute and 60 minutes; subjecting the joined cemented carbide mating member and maraging steel mating member to an annealing process at a temperature between 300°C and 600°C for a time between 5 minutes and 12 hours. A method comprising the above steps.

2. The method according to claim 1, wherein the filler contains at least 99 wt% Cu.

3. The method according to claim 1, wherein the Ni coating has a thickness between 2 μm and 10 μm and is deposited using PVD technology.

4. The method according to claim 1, wherein the maraging steel mating member contains 8 - 25 wt% Ni, one or more alloying elements selected from Co, Mo, Ti, Al and Cr in a total amount between 7 wt% and 27 wt%, and less than 0.03 wt% C, with the balance being Fe and impurities.

5. The method according to claim 1, wherein the maraging steel mating member contains 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, and less than 0.03 wt% C, with the balance being Fe and impurities.

6. The method according to claim 1, wherein the maraging steel mating member contains 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, and less than 0.03 wt% C, with the balance being Fe and impurities.

7. The method according to claim 1, wherein the brazing process is carried out at a temperature between 950°C and 1170°C for a time between 5 minutes and 30 minutes.

8. The method according to claim 1, wherein the tempering process is carried out at a temperature between 400°C and 600°C for a period between 2 hours and 5 hours.

9. A tool produced according to claim 1, comprising the maraging steel joint partner and the carbide joint partner, and a brazed joint for joining the maraging steel joint partner and the carbide joint partner.

10. The tool according to claim 9, wherein the brazed joint has a shear strength of at least 200 MPa.

11. The tool according to claim 9 or 10, wherein the maraging steel joint partner has a composition of 8 to 25% by weight of Ni, one or more alloying elements selected from Co, Mo, Ti, Al and Cr in a total amount between 7% and 27% by weight, and less than 0.03% by weight of C, the balance being Fe and impurities.

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