Tool and manufacturing method of it

Abstract

A tool includes a cemented carbide part and a steel part joined by brazing, where the steel part has an average hardness of between 390 and 510 HV30. The braze joint includes Ti and a TiC layer, with a thickness of between 0.03 and 5 m, adjoining to the cemented carbide part. The tool provides a strong braze joint and a steel part that have an even hardness.

Claims

1. A tool comprising: a cemented carbide part; a steel part having a composition of from 0.63 to 0.70 wt % C, from 1.40 to 1.60 wt % Si, from 1.35 to 1.55 wt % Mn, from 1.00 to 1.20 wt % Cr, from 0.23 to 0.27 wt % Mo, less than 0.25 wt % Ni, less than 0.025 wt % P, less than 0.0015 wt % S, and the balance Fe, and an average hardness of between 390 and 510 HV30 with a standard deviation between 0 and 30 HV30; and a braze joint joining the cemented carbide part and the steel part, wherein the braze joint includes Ti, and wherein the braze joint includes a TiC layer, with a thickness of between 0.03 and 5 m, adjoining the cemented carbide part.

2. The tool according to claim 1, wherein the steel part has an average hardness of between 420 and 480 HV30 with a standard deviation of between 0 and 15 HV1.

3. The tool according to claim 1, wherein the braze joint has a thickness of between 20 and 200 m.

4. The tool according to claim 1, wherein the braze joint includes Cu and Ag.

5. The tool according to claim 1, wherein the braze joint includes a composition of Ag in an amount of from 30 to 80 wt %, Cu in an amount of 15 to 65 wt %, In in an amount of 0 to 15 wt % and Ti in an amount of 0.3 to 15 wt %.

6. A method of making a tool according to claim 1 comprising the steps of: providing a cemented carbide part; providing a steel part having a composition of from 0.63 to 0.70 wt % C, from 1.40 to 1.60 wt % Si, from 1.35 to 1.55 wt % Mn, from 1.00 to 1.20 wt % Cr, from 0.23 to 0.27 wt % Mo, less than 0.25 wt % Ni, less than 0.025 wt % P, less than 0.0015 wt % S and the balance Fe; subjecting the cemented carbide part and the steel part with the braze material in between to a brazing step in a furnace at a temperature between 80 and 1100 C., for a time period of between 5 and 60 minutes and wherein the brazing takes place in an inert atmosphere at a pressure of between 10 to 400 mBar; after the brazing, subjecting the cemented carbide part and the steel part with the braze material in between into a quenching step by allowing an inert gas to flow into the furnace at a pressure of at least 400 mBar until a temperature of below 200 C. is reached; and subjecting at least the steel part to a tempering step at a temperature of between 300 and 700 C. for between 15 minutes and 3 hours.

7. The method of making a tool according to claim 6, wherein the brazing step is performed at a temperature between 850 and 980 C., for a time period of between 15 and 45 minutes.

8. The method of making a tool according to claim 6, wherein the inert atmosphere during brazing is Ar and/or N.sub.2.

9. The method of making a tool according to claim 6, wherein the temperature during the quenching is lowered at a rate of at least 30 C./minute.

10. The method of making a tool according to claim 6, wherein the inert gas used to flow into the furnace during quenching is one of Ar or N.sub.2, or a mixture thereof.

11. The method of making a tool according to claim 6, wherein the tempering step is performed at a temperature of between 400 and 650 C. for between 15 minutes to 3 hours.

12. The method of making a tool according to claim 6, wherein the braze material has a solidus temperature of between 488 and 1123 C. and a liquidus temperature of between 612 and 1180 C. and wherein the braze material, in addition to Ti, further includes one or more elements selected from Zn, Ag, Cu, Sn, In, Zr, Hf and Cr.

13. The method of making a tool according to claim 6, wherein the braze material includes Ag in an amount of from 30 to 80 wt %, Cu in an amount of 15 to 65 wt %, In in an amount of 0 to 15 wt %, and Ti in an amount of 0.3 to 15 wt %.

14. The method of making a tool according to claim 6, wherein a clamping force of between 0.5 to 10 MPa is applied during the brazing step.

Description

FIGURES

(1) FIG. 1 shows a SEM image of the braze joint according to the invention at a magnification of 1000 where A is the steel part, B is the braze joint, C is the cemented carbide part and D is the TiC layer.

(2) FIG. 2 shows a SEM image of a braze joint according to the invention at a magnification of 1500.

(3) FIG. 3 shows a SEM image of a braze joint according to the invention at a magnification of 10000 where B is the braze joint, C is the cemented carbide part, D is the TiC layer and E is the Ti-accumulation layer.

(4) FIG. 4 shows a SEM image of a braze joint according to the invention at the interface between the braze joint and the steel part at a magnification of 10000 where A is the steel part, B is the braze joint and F is the TiC layer at the steel surface.

(5) FIG. 5 shows the hardness profile of a tool where induction heating has been used. A is the steel part, B is the braze joint and C is the cemented carbide.

(6) FIG. 6 shows the steps for the claimed method where A is providing a cemented carbide part, B is providing a steel part, C is placing a braze material between the cemented carbide part and the steel part. D is the brazing step, E is the quenching step and F is the tempering step.

EXAMPLE 1 (INVENTION)

(7) A steel part made of a bearing steel grade Ovako 677 with a composition of 0.63-0.70 wt % C, 1.4-1.6 wt % Si, 1.35-1.55 wt % Mn, 1-1.2 wt % Cr, 0.23-0.27 wt % Mo and the remaining Fe was provided together with a cemented carbide part with a composition of 10 wt % Co and the remaining WC.

(8) The braze material was provided in the form of a paste in an amount enough to cover the surface to be joined. The braze material had a composition of 70 wt % Ag, 28 wt % Cu and 2 wt % Ti.

(9) The paste was placed between the steel part and the cemented carbide part so that both pieces were in contact with the paste. The assembled joined pieces were then placed into a vacuum sintering furnace, PVA COV 231, where a vacuum of 10.sup.2 mBar was first achieved to remove all oxygen after which an inert atmosphere, Ar at 50 mBar, was introduced, The temperature was first increased to 250 C. which was held for 5 minutes and then a second stop at 550 C. for 5 minutes. The brazing temperature 880 C. was kept for 30 minutes after which the pieces were quenched by flowing Ar gas at a pressure of 600 mBar into the furnace until the temperature was below 150 C.

(10) After the brazing/quenching step, the brazed pieces were subjected to an tempering process to retain the hardness of the steel. The pieces were placed into a furnace where the pieces was heated in an inert atmosphere, 50 mBar Ar, to a temperature 550 C. which was kept for 30 minutes after which the pieces were cooled down.

(11) The sample are herein denoted Invention 1.

EXAMPLE 2 (COMPARATIVE 2)

(12) A steel part made Uddeholm Idun with a composition of 0.21 wt % C, 0.9 wt % Si, 0.45 wt % Mn, 13.5 wt % Cr, 0.2 wt % Mo, 0.6 wt % Ni and 0.25 wt % V and the remaining Fe was provided together with a cemented carbide part with a composition of 10 wt % Co and the remaining WC.

(13) The braze material was provided in the form of a paste in an amount enough to cover the surface to be joined. The braze material had a composition of 70 wt % Ag, 28 wt % Cu and 2 wt % Ti.

(14) The paste was placed between the steel part and the cemented carbide part so that both pieces were in contact with the paste. The assembled joined pieces were then placed into a vacuum sintering furnace, PVA COV 231, where a vacuum of 10.sup.2 mBar was first achieved to remove all oxygen after which an inert atmosphere, Ar at 50 mBar, was introduced, The temperature was first increased to 250 C. which was held for 5 minutes and then a second stop at 550 C. for 5 minutes. The brazing temperature 880 C. was kept for 30 minutes after which the pieces were quenched by flowing Ar gas at a pressure of 600 mBar into the furnace until the temperature was below 150 C.

(15) After the brazing/quenching step, the brazed pieces were subjected to an tempering process to retain the hardness of the steel. The pieces were placed into a furnace where the pieces was heated in an inert atmosphere, 50 mBar Ar, to a temperature 550 C. which was kept for 30 minutes after which the pieces were cooled down to below 100 C. after which the pieces were once more heated to a temperature 550 C. which was kept for 30 minutes after which the pieces were cooled down. The dual tempering cycle was recommended for this steel type. The sample are herein denoted Comparative 1.

EXAMPLE 3 (COMPARATIVE)

(16) A steel part made of steel 1.6582 (34CrNiMo6) was provided together with a cemented carbide part with a composition of 10 wt % Co and 0.4 wt % Cr and the remaining WC.

(17) The braze material was Ag49Zn23Cu16Mn7.5Ni4.5 in the form of a wire which was applied as a ring with a diameter of 1-2 mm.

(18) The pieces were joined by induction heating using a coil by rapidly heating the braze joint to 700 C. and hold for 15 s, after which the powder is turned off and the tool is allowed to cool to room temperature. In FIG. 5 the hardness values of the steel part are shown where the measuring points is placed along a line from a distance from the braze joint in the steel part and over the braze joint to the cemented carbide part.

(19) The sample are herein denoted Comparative 2.

EXAMPLE 4 (COMPARATIVE)

(20) 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.

(21) The braze material was provided in the form of a foil with a thickness of 100 m. The braze metal had a composition of 100 wt % Cu. The melting temperature is 1085 C.

(22) The foil was placed between the 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 C./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 C./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.

(23) Subsequently, the cemented carbide-steel joint with the carbon-hardening hot-work steel 1.2344 was tempered at 630 C. for 2 h two times.

(24) The sample will herein be denoted Comparative 3.

EXAMPLE 5

(25) The hardness was measured using a Vickers hardness tester applying a load of 30 kgf (for HV30) and 1 kgf for (HV1). The load was applied for 15 s.

(26) To analyze the interface between the braze joint and the cemented carbide on Invention 1 and Comparative 2 SEM-EDS technique was used. The SEM used was a Zeiss Sigma VP with an Oxford Instruments NordlysMax.sup.2 EBSD-detector and provided with Oxford Instruments X-Max.sup.N EDS-system.

(27) The thickness of the TiC layer in the braze joints of Invention 1 and Comparative 1 was measured on a SEM image at a magnification of 1000. The TiC layer was identified by visual appearance in the back scattered electron mode. In FIGS. 1 and 2, SEM images of Invention 1 is shown where the TiC layer is clearly visible. The values of the thickness of the TiC layer given in Table 1 is an average of 3 measurements, all taken in the middle of the braze joint, i.e. far from the edges.

(28) Using EDS, the accumulation of Ti can be identified in the SEM image and measured as a Ti-accumulation layer. By accumulation layer is herein meant the thickness of the accumulation identified in the SEM image and identified by EDS, see FIG. 3. The values in Table 1 is an estimation from visual inspection of the SEM image and is therefore given as an interval.

(29) TABLE-US-00001 TABLE 1 Ti- Shear TiC accumulation strength layer layer Standard (MPa) (m) (m) Hardness deviation Invention 1 n.a. 0.8 4-5 453 HV30 26 Comparative 1 n.a. 0.5 2 317 HV30 5 Comparative 2 N/A No TiC No Ti acc. 430 HV1 141 layer layer Comparative 3 17.1 0* 0 494 HV1 5 *No Ti in braze material