METHOD OF MAKING A TOOL

Abstract

A method of making a tool having a joining a maraging steel joining partner and a cemented carbide joining partner by brazing and a tool made according to the method is provided. The method includes depositing a Ni coating onto the maraging steel joining partner prior to applying the filler material having at least 70 wt % Cu. The braze joint shows excellent shear strength.

Claims

1. A method of 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 with a thickness of between 0.5 and 15 m on a joining surface of the maraging steel joining partner: placing a filler material including at least 70 wt % Cu in contact with the cemented carbide joining partner and the joining surface of the maraging steel joining partner: subjecting the cemented carbide joining partner and the maraging joining partner with the filler material in between to a brazing process at an elevated temperature in a vacuum furnace at a temperature between 90 and 1200 C., for a time period of between 1 and 60 minutes; and subjecting the joined cemented carbide joining partner and maraging joining partner to a tempering process at a temperature of between 300 and 600 C. for between 5 minutes and 12 hours.

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

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

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

5. The method according to claim 1, wherein the maraging steel includes 11 to 25 wt % Ni, 7 to 15 wt % Co, from 3 to 10 wt % Mo, 0.1 to 1.6 wt % Ti, from 0 to 0.15 wt % Cr, from 0 to 0.2 wt % Al, and less than 0.03 wt % C with a balance of Fe and impurities.

6. The method according to claim 1, wherein the maraging steel includes 15 to 25 wt % Ni, 8.5 to 12.5 wt % Co, from 3 to 6 wt % Mo, 0.5 to 1.2 wt % Ti, from 0 to 0.15 wt % Cr, from 0 to 0.2 wt % Al, less than 0.03 wt % C with a balance of Fe and impurities.

7. The method according to claim 1, wherein the brazing process takes place at a temperature of between 95 and 1170 C. for between 5 and 30 minutes.

8. The method according to claim 1, wherein the tempering process takes place at a temperature of between 400 and 600 C. for between 2 and 5 hours.

9. A tool made according to claim 1, the tool comprising the maraging steel joining partner and the cemented carbide joining partner and the braze joint joining the maraging steel and cemented carbide joining partners.

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

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 shows a schematic drawing of the shearing test device where 1 is the steel joining member and 2 is the cemented carbide joining member.

[0046] FIG. 2 shows a SEM image of a braze joint according to the present invention where a Ni coating was deposited onto the steel joining partner prior to brazing where A is the cemented carbide joining member B is the brazing joint and C is the maraging steel joining member.

[0047] FIG. 3 shows a SEM image of a braze joint according to prior art where no Ni coating was deposited onto the steel joining partner prior to brazing where A is the cemented carbide joining member B is the brazing joint and C is the maraging steel joining member.

DETAILED DESCRIPTION

Example 1

[0048] Steel parts made of maraging steel 1.2709 in the form of a cylinder were provided together with cemented carbide parts with a composition of 10 wt % Co, 1 wt % other carbides and the remaining WC. The maraging steel had a hardness of approx. 340 HV1 prior to brazing.

[0049] Onto a part of the maraging steel parts a Ni coating was deposited using arc PVD (physical vapor deposition). The samples were first ion etched (100A, 1,000 V bias voltage, 3 Ah) and then the Ni coating was deposited using 90A, 30V bias voltage and 90 Ah until a thickness of 5 um was reached.

[0050] The filler material was provided in the form of a foil with a thickness of 100 m. The composition of the filler material was 100% Cu.

[0051] 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 joining pieces were then placed into a Schmetz vacuum furnace where the temperature was first increased to 650 C. at a rate of 20 C./min and kept there for 10 minutes. The pieces were then heated up to 850 C. at a rate of 20 C./min and kept there for 10 minutes. After that, the temperature was increased up to the brazing temperature of 1100 C. at a rate of 5 C./min. The brazing temperature 1100 C. was kept for 15 minutes after which the pieces were cooled down to 300 C. at a rate of 5 C./min. After 300 C. it was free cooling.

[0052] After the brazing step, the brazed pieces were subjected to an aging process to increase the hardness of the maraging steel. The pieces were placed in the same furnace as the brazing where the temperature was increased to the aging temperature at a rate of 5 C./min. The aging temperature 580 C. was kept for 3h after which the pieces were cooled down to 300 C. at a rate of 5 C./min. After 300 C. it was free cooling.

[0053] The joined pieces where the maraging steel has been provided with a Ni coating is herein called Invention 1 whereas the joined pieces where the maraging steel was not provided with a Ni coating is herein called Comparative 1.

[0054] A SEM image of the braze joint of Invention 1 is shown in FIG. 2 and a SEM image of the braze joint of Comparative 1 is shown in FIG. 3. As can be seen in FIG. 3, the braze joint contains some irregularities and defects closest to the steel part.

[0055] An excellent wetting with no signs of thermal stress crack could be observed, proven by the high shear test result.

Example 2 (Comparative)

[0056] A steel part made of the carbon-hardening hot-work steel 1.2344 was provided together with a cemented carbide part with a composition of 10 wt % Co, 1 wt % other carbides and the remaining WC.

[0057] The filler material was provided in the form of a foil with a thickness of 100 m. The braze metal had a composition of 100.0 wt % Cu. The melting temperature is 1085 C.

[0058] The foil was placed between the maraging steel part and the cemented carbide part and assembled joining pieces were placed into the furnace where the temperature was first increased to 650 C. at a rate of 20 C./min and hold for 5 minutes. From 650 C. the temperature was then increase by a rate of 10 K/min to the brazing temperature T.sub.Brazing, which was 1100 C. T.sub.Brazing was kept for a dwell time of 15 min, after which the pieces were cooled down to 850 C. with a cooling rate of 50 K/min. From 850 C., the specimens were N.sub.2-quenched with an overpressure of 2 bars and a fan frequency of 2500 min.sup.1.

[0059] Subsequently, the cemented carbide-steel joint with the carbon-hardening hot-work steel 1.2344 was aged at 630 C. for 2 h two times.

[0060] The sample will herein be denoted Comparative 2.

Example 3

[0061] The joined pieces were evaluated by measuring the shear strength of the brazed joint, the hardness of the maraging steel part and the braze joint were investigated for cracks etc. In order to assess the joint strength properties, the samples were shear tested using a shear device set-up as shown in FIG. 1 where 1 is the steel part in the shape of a steel cylinder (=20 mm, h=5 mm) and 2 is the cemented carbide part in the shape of a cemented carbide cylinder (=10 mm, h=5 mm. The steel cylinder is positioned in the gap of the shear strength test device and therefore can only be moved in loading direction. A notch, which was eroded into the surface of the device, holds the joined parts in the right position and guarantees an evenly distributed force induction into the braze joint. The applied force was constantly increased until the braze joint failed and the cemented carbide cylinder sheared off. The ultimate shear strength was then calculated by the quotient of the maximal measured force and the initial joining surface (A=78,5 mm.sup.2). The filler material was not removed before the determination of brazed joint shear strength. When a rod was tested, the same method was applied.

[0062] The hardness of the steel parts was measured by a Vickers hardness tester on a cross section of the maraging steel part, applying a load of 1 kgf (kilogram force) and a loading time of 15 s. A pattern of 36 indents covering the complete profile (ca. 205 mm.sup.2) of the of the steel part in the cross-section was applied.

TABLE-US-00001 TABLE 1 Shear strength (MPa) Hardness (HV1) Invention 1 327 427 Comparative 1 152 427 Comparative 2 17.1 494