CLIAMS:1. A cold forging die/pellet comprising:
one or more components formed of sintered cemented carbide including a tungsten carbide component and a metallic binder component, the metallic binder component present in an amount of at least 20 wt.% of the sintered cemented carbide, wherein the metallic binder component comprises cobalt, nickel and chromium.

2. The cold forging die/pellet of claim 1, wherein the metallic binder component is present in an amount of 22-28 wt.% of the sintered cemented carbide.

3. The cold forging die/pellet of claim 1, wherein the chromium is present in an amount of 0.5 to 2 wt.% of the sintered cemented carbide.

4. The cold forging die/pellet of claim 1, wherein the chromium is present in an amount of 0.7 to 1.5 wt.% of the sintered cemented carbide.

5. The cold forging die/pellet of claim 1, wherein the nickel is present in an amount of 3-7 wt.% of the sintered cemented carbide.

6. The cold forging die/pellet of claim 5, wherein the cobalt is present in an amount of 15-20 wt.% of the sintered cemented carbide.

7. The cold forging die/pellet of claim 1, wherein the sintered cemented carbide has hardness of 750-950 HV30.

8. The cold forging die/pellet of claim 1, wherein the sintered cemented carbide has density of 13-13.5 g/cm2.

9. The cold forging die/pellet of claim 1, wherein tungsten carbide component comprises tungsten carbide particles having an average grain size of 1-10 µm.

10. The cold forging die/pellet of claim 5, wherein the tungsten carbide component is present in an amount of 72-78 wt.% of the sintered cemented carbide.

11. The cold forging die/pellet of claim 1, wherein the one or more components are selected from an extrusion die, an extrusion punch and a forming punch.

12. A method of forming a component of cold forging die/pellet comprising:
providing a grade powder composition comprising a tungsten carbide component and a powder metallic binder component, the powder metallic binder component present in an amount of at least 20 wt.% of the grade powder composition, wherein the powder metallic binder component comprises cobalt, nickel and chromium;
forming the grade powder composition into a green article; and
sintering the green article to provide the cold forging component formed from sintered cemented carbide.

13. The method of claim 12, wherein the metallic binder component is present in an amount of 22-28 wt.% of the grade powder composition.

14. The method of claim 12, wherein the chromium is present in an amount of 0.5 to 2 wt.% of the grade powder composition.

15. The method of claim 12, wherein the nickel is present in an amount of 3-7 wt.% of the grade powder composition.

16. The method of claim 15, wherein cobalt is present in an amount of 15-20 wt.% of the grade powder composition.

17. The method of claim 12, wherein the tungsten carbide component comprises tungsten carbide particles having an average grain size of 1-10 µm.

18. The method of claim 17, wherein the tungsten carbide particles are coated with the powder metallic binder component.

19. The method of claim 12, wherein the component is selected from an extrusion die, an extrusion punch and a forming punch.

20. The method of claim 12 further comprising mechanically working the sintered cemented carbide.

21. A method of cold forging comprising:
providing a bulk metal or alloy workpiece; and
subjecting the bulk metal or alloy workpiece to a cold forging process with an die/pellet comprising one or more components formed of sintered cemented carbide including a tungsten carbide component and a metallic binder component, the metallic binder component present in an amount of at least 20 wt.% of the sintered cemented carbide, wherein the metallic binder component comprises cobalt, nickel and chromium.

22. The method of claim 21, wherein the chromium present in an amount of 0.5 to 2 wt.% of the sintered cemented carbide.
,TagSPECI:TECHNICAL FIELD

The present invention relates to grade powder compositions and, in particular, to grade powder compositions comprising alloy binder of cobalt, nickel and chromium for cold forging applications.

BACKGROUND OF THE DISCLOSURE

Cold forging is a general term covering several different processes related by the forming or forging of bulk material at room temperature. As implied by the name, cold forging does not require workpiece heating for the forging operation. Several examples of cold forging operations include cold extrusion, cold heading, coining, ironing and nosing. Various materials can be employed in cold forging tooling. Extrusion punches, for example, can be formed of tool steels heat treated to a hardness of 62 to 66 HRC and exhibit high compressive yield strength. Similarly, die inserts can be fabricated from D2, M2 and M4 tool steels heat treated to 58 to 64 HRC. Cold forging tooling can also be formed of carbide. Hardmetal grades employing cobalt binder are commonly used in cold forging die fabrication and provide sufficient hardness and toughness. However, such hardness and toughness are achieved at the expense of carbide wear resistance.

SUMMARY OF THE DISCLOSURE

In one aspect, sintered cemented carbides are described herein for fabrication of cold forging die/pellet exhibiting enhanced wear resistance in addition to desirable hardness and toughness. For example, a cold forging die/pellet described herein comprises one or more components formed of sintered cemented carbide including a tungsten carbide (WC) component and a metallic binder component. The metallic binder component is present in an amount of at least 20 wt.% of the sintered cemented carbide, and the metallic binder component comprises cobalt, nickel and chromium. In some embodiments, chromium of the metallic binder is present in an amount of 0.5 to 2 wt.% of the sintered cemented carbide.

In another aspect, methods of forming components of cold forging die/pellet are described herein. A method of forming a component of cold forging die/pellet comprises providing a grade powder composition including a tungsten carbide component and a powder metallic binder component. The powder metallic binder component is present in an amount of at least 20 wt.% of the grade powder composition and comprises cobalt, nickel and chromium. The grade powder composition is formed into a green article, and the green article is sintered to provide the cold forging component formed of sintered cemented carbide. In some embodiments, the method further comprises mechanically working the sintered cemented carbide to place the cold forging component in final form. Alternatively, the sintered cemented carbide is provided in near-net shape form.

In a further aspect, methods of cold forging are described herein. A method of cold forging comprises providing a bulk metal or alloy workpiece and subjecting the workpiece to a cold forging process with an die/pellet comprising one or more components formed of sintered cemented carbide including a tungsten carbide component and a metallic binder component. The metallic binder component is present in an amount greater than or equal to 20 wt.% of the sintered cemented carbide and comprises cobalt, nickel and chromium. These and other embodiments are further described in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a general process for fabricating cold forging extrusion dies according some embodiments described herein.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by reference to the following detailed description and examples and their previous and following descriptions. Elements, die/pellet and methods described herein, however, are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

I. Cold Forging Components
In one aspect, sintered cemented carbides are described herein for fabrication of cold forging die/pellet exhibiting enhanced wear resistance in addition to desirable hardness and toughness. A cold forging die/pellet, in some embodiments, comprises one or more components formed of sintered cemented carbide including a tungsten carbide component and a metallic binder component. The metallic binder component is present in an amount greater than or equal to 20 wt.% of the sintered cemented carbide, and the metallic binder component comprises cobalt, nickel and chromium.

Turning now to specific components, sintered cemented carbide of the cold forging component comprises a tungsten carbide component including tungsten carbide particles. The tungsten carbide particles can have any size not inconsistent with the objectives of the present invention. For example, the tungsten carbide particles have an average grain size of 1 µm to 10 µm. In some embodiments, the tungsten carbide particles have an average grain size selected from Table I.

Table I – Average WC Grain Size (µm):

1-5
1.5-2.5
2.5-6
> 6
6-10

Moreover, the tungsten carbide particles can exhibit single-mode or multi-mode grain size distributions. The tungsten carbide component can be present in the sintered cemented carbide in an amount of at least about 70 wt%. In some embodiments, the tungsten carbide component is present in an amount of 70-80 wt% of the sintered cemented carbide. In further embodiments, the tungsten carbide component can be present in an amount of 73-78 wt.% of the sintered cemented carbide.

As described herein, the sintered cemented carbide also comprises a metallic binder component in an amount of at least 20 wt.%. In some embodiments, the metallic binder component is present in the sintered cemented carbide in an amount selected from Table II.

Table II – Metallic Binder Component (wt.%)

20-30
21-30
22-28
22-27

The metallic binder comprises cobalt, nickel and chromium. Chromium can be present in the metallic binder in any amount not inconsistent with the objectives of the present invention. For example, chromium of the metallic binder can be present in an amount of 0.5 to 2 wt.% of the sintered cemented carbide. In some embodiments, chromium of the metallic binder is present in the sintered cemented carbide in an amount selected from Table III.

Table III – Cr (wt.% of sintered cemented carbide)

0.7-1.5
0.8-1.3
1-1.5
1-2

Moreover, nickel and cobalt of the metallic binder component can be present in the sintered cemented carbide in amounts selected from Tables IV and V respectively.

Table IV – Ni (wt.% of sintered cemented carbide)

2-8
3-7
4-6
4.5-5.5
Table V – Co (wt.% of sintered cemented carbide)

15-20
16-19
16-18
16.5-18.5

Sintered cemented carbide of the cold forging component exhibits properties suitable for one or more cold forging applications. For example, the sintered cemented carbide can have hardness of 750-950 HV30. HV30 refers to Vickers Hardness using a 30 kilogram-force load. Vickers hardness values recited herein are determined according to ASTM E 384, “Standard Method for Knoop and Vickers Hardness of Materials,” ASTM International. The sintered cemented carbide, in some embodiments, has hardness of 840-950 HV30 or 840-890 HV30. Additionally, the sintered cemented carbide has density of 13-14 g/cm3. For example, the sintered cemented carbide can have density of 13.1-13.5 g/cm3 or 13.2-13.4 g/cm3.

Various cold forging components can be formed of the sintered cemented carbide described in this Section I. For example, the cold forging component can be employed in forward or backward extrusion tooling. The die, extrusion punch and/or the forming punch may be formed of the sintered cemented carbide composition described in this Section I. One or more components of cold heading die/pellet, coining die/pellet, ironing die/pellet and/or nosing die/pellet may also be formed of the sintered cemented carbide composition.

Components of cold forging die/pellet can be formed by powder metallurgical techniques. For example, a method of forming a component of a cold forging die/pellet comprises providing a grade powder composition including a tungsten carbide component and a powder metallic binder component. The powder metallic binder component is present in an amount of at least 20 wt.% of the grade powder composition and comprises cobalt, nickel and chromium. The grade powder composition is formed into a green article, and the green article is sintered to provide the cold forging component formed of sintered cemented carbide. In some embodiments, the method further comprises mechanically working the sintered carbide to place the cold forging component in final form. Alternatively, the sintered cemented carbide is provided in near-net shape form.

The grade powder composition, in some embodiments, is provided by mixing tungsten carbide particles and the powder metallic binder. In some embodiments, the amount of powder metallic binder employed in the grade powder composition is selected from Table II herein. The resulting mixture is subjected to milling. For example, the mixture of tungsten carbide particles and powder metallic binder can be milled in a ball mill or attritor. Milling of the mixture can result in tungsten carbide particles being coated with powder metallic binder. The powder metallic binder can be provided in various forms for mixing with the tungsten carbide particles. In some embodiments, the powder metallic binder is provided in prealloyed form. In such embodiments, cobalt, nickel and chromium are prealloyed in the desired amounts, including amounts selected from Tables III-V herein. Alternatively, powder cobalt, powder nickel and powder chromium can be separately added in the desired amounts, including amounts selected from Tables III-V, to form the metallic binder. Alternatively, chromium is added to the powder metallic binder as chromium carbide, such as Cr3C2. In additional embodiments, cobalt and nickel can be provided as a prealloyed powder and chromium carbide added to the prealloyed powder to complete the metallic binder.

The grade powder is formed or consolidated into a green article in preparation for sintering. Any consolidation method can be employed not inconsistent with the objectives of the present invention. The grade powder, for example, can be pressed or molded, including injection molded into a green article. The green article can take the form of a blank or can assume near-net shape form of the cold forging component. In some embodiments, the green article is mechanically worked to provide the desired shape.

The green article is subsequently sintered to provide the cold forging component formed of sintered cemented carbide. In embodiments wherein the green article exhibits a blank format, the resulting sintered carbide blank can be mechanically worked to complete the cold forging component. For example, a sintered carbide blank can be bored to provide an extrusion die. The green article can be vacuum sintered or sintered under a hydrogen atmosphere. During vacuum sintering, the green part is placed in a vacuum furnace and sintered at temperatures of 1320oC to 1500oC. In some embodiments, hot isostatic pressing (HIP) is added to the vacuum sintering process. Hot isostatic pressing can be administered as a post-sinter operation or during vacuum sintering yielding a sinter-HIP process. The resulting sintered cemented carbide exhibits the hardness and density values detailed above.

II. Methods of Cold Forging

In a further aspect, methods of cold forging are described herein. A method of cold forging comprises providing a bulk metal or alloy workpiece and subjecting the workpiece to a cold forging process with an die/pellet comprising one or more components formed of sintered cemented carbide described in Section I. Cold forging processes contemplated include cold extrusion, cold heading, coining, ironing and nosing. As detailed in the following example, cold forging components formed of sintered cemented carbide herein exhibit enhanced wear resistance and lifetimes relative to cold forging components formed of sintered cemented carbides employing cobalt metallic binder.

EXAMPLE 1 – Cold Forging Extrusion Dies

Cold forging pellets were formed of sintered cemented carbide grades A and B described herein having target compositional parameters and properties provided in Table VI. The pellets were employed in cold forging dies as follows:
Product 1 – 2nd Heading/Extrusion Die M5 x 21 HHCB
Product 2 – 3rd Station Taper Font Die for M8 x 1.25 Flange
Product 3 – 3rd Station Taper Front Die for M8 x 1.25 x 25 Flange

Figure 1 illustrates a general process for fabricating cold forging dies according to some embodiments described herein. Pellets for Products 1-3 were also formed from prior sintered cemented carbide grade C having target compositional parameters and properties provided in Table VI.

Table VI – Sintered Cemented Carbide Grade Properties

Grade Target Sintered Cemented Carbide Composition (wt.%) Microstructure and Properties
WC Co Ni Cr3C2 WC grain size, (?m) Hardness (HV30) Density
(g/cm3)
A 76.846 17 5 1.154 3-5 850-860 13.2-13.5
B 76.846 18 4 1.154 3-5 850-875 13.3-13.4
C 75 25 0 0 2.5-4.5 750-865 13.1-13.4

Cold forging dies were subjected to lifetime testing according to Tables VII and VIII below:

Table VII – Lifetime Testing of Product 1

Product Description Grade A WC-23%(Co-Ni-Cr) Grade B WC-23%(Co-Ni-Cr) Grade C WC-25%(Co)
Life in no. of components Failure Pattern Life in no. of components Failure Pattern Life in no. of components Failure Pattern
1 M8 x 1.25 Flange
25 lacs
over size
8.93 lacs Lining in extrusion profile
6-6.5 lacs
Wear
7-time Re-lapping 2-time Re-lapping 5-time Re-lapping
Average Life/lapping 312500 297667 104167

Table VIII – Lifetime Testing of Products 2 and 3

Product Description Grade A WC-23%(Co-Ni-Cr) Grade B WC-23%(Co-Ni-Cr) Grade C WC-25%(Co)
Life in no. of components Failure Pattern Life in no. of components Failure Pattern Life in no. of components Failure Pattern
2 M8 x 1.25 x 25 Flange
230,000+
Stopped
800,000
Cracked 70,000-75,000
Crack/Wear Out
3 M8 x 1.25 x 30 Flange
248,000

Over Size
-
- 70,000-75,000 Crack/Wear Out

As provided in Tables VII and VIII, cold forging dies employing pellets formed of sintered cemented carbides A and B described herein exhibited significant lifetime enhancements relative to cold forging dies employing pellets formed of prior sintered cemented carbide C.

Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.