COBALT-FREE TUNGSTEN CARBIDE-BASED HARD-METAL MATERIAL

Abstract

A cobalt-free, tungsten carbide-based cemented carbide material includes 70-97 wt % of hard substance particles formed at least predominantly by tungsten carbide, and 3-30 wt % of a metallic binder which is an iron-nickel-based alloy. The iron-nickel-based alloy includes at least iron, nickel and chromium, with a ratio of Fe to (Ni+Fe) of 0.70≤Fe/(Fe+Ni)≤0.95; a Cr content of 0.5 wt %≤Cr/(Fe+Ni+Cr) and (i) for the range 0.7≤Fe/(Fe+Ni)≤0.83: Cr/(Fe+Ni+Cr)≤(−0.625*(Fe/(Fe+Ni))+3.2688) wt %; (ii) for the range 0.83≤Fe/(Fe+Ni)≤0.85: Cr/(Fe+Ni+Cr)≤(−27.5*(Fe/(Fe+Ni))+25.575) wt %; and (iii) for the range 0.85≤Fe/(Fe+Ni)≤0.95: Cr/(Fe+Ni+Cr)≤2.2 wt %; an optional Mo content, an optional V content, and unavoidable impurities up to in total not more than 1 wt % of the cemented carbide material.

Claims

1-10. (canceled)

11. A cobalt-free, tungsten carbide-based cemented carbide material, comprising: 70-97 wt % of hard substance particles formed at least predominantly by tungsten carbide; and 3-30 wt % of a metallic binder being an iron-nickel-based alloy with at least iron, nickel and chromium; with a Cr content of 0.5 wt %≤Cr/(Fe+Ni+Cr) and a ratio of Fe to (Ni+Fe) being 0.70≤Fe/(Fe+Ni)≤0.95; (i) for a range 0.70≤Fe/(Fe+Ni)≤0.83: Cr/(Fe+Ni+Cr)≤(−0.625*(Fe/(Fe+Ni))+3.2688) wt % (ii) for a range 0.83≤Fe/(Fe+Ni)≤0.85: Cr/(Fe+Ni+Cr)≤(−27.5*(Fe/(Fe+Ni))+25.575) wt % (iii) for a range 0.85≤Fe/(Fe+Ni)≤0.95: Cr/(Fe+Ni+Cr)≤2.2 wt %; an optional Mo content relative to (Fe+Ni+Cr) of 0 wt %≤Mo/(Fe+Ni+Cr)≤10 wt %; an optional V content relative to (Fe+Ni+Cr) of 0 wt %≤V/(Fe+Ni+Cr)≤2 wt %; and unavoidable impurities up to a total of not more than 1 wt % of the cemented carbide material.

12. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein Fe/(Fe+Ni)≤0.90.

13. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 12, wherein 0.75≤Fe/(Fe+Ni)≤0.90.

14. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein the metallic binder amounts to 5-25 wt %.

15. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein the following holds for the optional Mo content: 0 wt %≤Mo/(Fe+Ni+Cr)≤6 wt %.

16. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein the following holds for the V content: V/(Fe+Ni+Cr)≤1 wt %.

17. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein the following holds for the Cr content: Cr/(Fe+Ni+Cr)≥1.5 wt %.

18. The cobalt-free, tungsten carbide-based cemented carbide material of claim 17, wherein Cr/(Fe+Ni+Cr)≥2.0 wt %.

19. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, wherein Cr/(Fe+Ni+Cr)≤2.2 wt %.

20. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 11, comprising tungsten carbide particles having a mean size of 0.05-12 μm.

21. The cobalt-free, tungsten carbide-based cemented carbide material according to claim 17, comprising tungsten carbide particles having a mean size of 0.1-6 μm.

Description

[0033] Further advantages and practicalities of the invention are apparent from the following description of working examples with reference to the appended figures.

[0034] In the figures:

[0035] FIG. 1 shows a calculated phase diagram for a cemented carbide composition of tungsten carbide with 9.2 wt % of a metallic iron-nickel binder having an Fe/(Fe+Ni) ratio of 0.85 and having a chromium content of Cr/(Fe+Ni+Cr)=2.2 wt %;

[0036] FIG. 2 shows a calculated phase diagram for a cemented carbide composition of tungsten carbide with 9.2 wt % of a metallic iron-nickel binder having an Fe/(Fe+Ni) ratio of 0.85 and having a chromium content of Cr/(Fe+Ni+Cr)=2.6 wt %;

[0037] FIG. 3 shows a calculated phase diagram corresponding to FIG. 1 and FIG. 2, but for a chromium content of Cr/(Fe+Ni+Cr)=3.0 wt %;

[0038] FIG. 4 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type F;

[0039] FIG. 5 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type G;

[0040] FIG. 6 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type H;

[0041] FIG. 7 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type I;

[0042] FIG. 8 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type J;

[0043] FIG. 9 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type K;

[0044] FIG. 10 shows an optical micrograph with 500-fold magnification of the cemented carbide material of type K with shorter pretreatment by etching;

[0045] FIG. 11 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type M; and

[0046] FIG. 12 shows an optical micrograph with 1500-fold magnification of the cemented carbide material of type P.

EMBODIMENT

[0047] An embodiment of the cobalt-free, tungsten carbide-based cemented carbide material is first described generally below.

[0048] The cemented carbide material has a specific composition, which is described in more detail below.

[0049] The cemented carbide material consists predominantly, to an extent of 70-97 wt %, of hard substance particles which are formed at least predominantly by tungsten carbide. These hard substance particles may consist of tungsten carbide. The cemented carbide material also has 3-30 wt % of a metallic binder. The fraction of the metallic binder may preferably be 5-25 wt % of the cemented carbide material. The metallic binder is an iron-nickel-based alloy, thus comprising iron and nickel as principal constituents. Besides iron and nickel, the metallic binder comprises at least chromium. The cemented carbide material is cobalt-free, meaning that it contains no cobalt or comprises at most traces of cobalt as unavoidable impurities. The cemented carbide material may also, optionally, have up to 10 wt % of molybdenum in relation to the total amount of iron, nickel and chromium, i.e., Mo/(Fe+Ni+Cr)≤10 wt %, up to a maximum of 2 wt % of vanadium in relation to the total amount of iron, nickel and chromium, i.e., V/(Fe+Ni+Cr)≤2 wt %, and also up to in total not more than 1 wt % of unavoidable impurities in the cemented carbide material. Preferably for the Mo content: Mo/(Fe+Ni+Cr)≤6 wt %. Preferably for the V content: V/(Fe+Ni+Cr)≤1 wt %.

[0050] The iron-nickel-based alloy of the metallic binder has a higher fraction of iron than of nickel. The iron fraction here is 70-95 wt % of the total amount (Fe+Ni) of iron and nickel. The iron fraction is preferably not more than 90 wt % of the total amount of iron and nickel, more preferably 75-90 wt % of the total amount of iron and nickel.

[0051] The chromium content of the cemented carbide material is at least 0.5 wt % of the total amount (Fe+Ni+Cr) of iron, nickel and chromium. The chromium content may preferably be at least 1.5 wt % of the total amount of iron, nickel and chromium, more preferably at least 2.0 wt %. In the event of an iron-nickel ratio in the range 0.7≤Fe/(Fe+Ni)≤0.83, the chromium content in relation to the total content (Fe+Ni+Cr) is at most (−0.625*(Fe/(Fe+Ni))+3.2688) wt %. In the case of an iron-nickel ratio in the range 0.83≤Fe/(Fe+Ni)≤0.85, the chromium content in relation to the total content (Fe+Ni+Cr) is at most (−27.5 (Fe/(Fe+Ni))+25.575) wt %. In the case of an even higher iron fraction, the chromium content in relation to the total content (Fe+Ni+Cr) is at most 2.2 wt %.

[0052] In the text below, with reference to the calculated phase diagrams of FIGS. 1 to FIG. 3, an illustrative, in-depth explanation is given of the problems which arise, for the industrial production of cobalt-free, tungsten carbide-based cemented carbide material with a metallic binder formed by an iron-nickel-based alloy, when chromium is added. In the phase diagrams of FIG. 1 to FIG. 3, the carbon content in wt % is plotted in each case on the horizontal axis. The phase diagrams were calculated for a cemented carbide material having a composition of 9.2 wt % of metallic, iron-nickel-based alloy binder with a ratio of Fe/(Fe+Ni) of 85 wt %, Cr/(Fe+Ni+Cr)=2.2 wt % (FIG. 1) or 2.6 wt % (FIG. 2) or 3.0 wt % (FIG. 3), the balance being tungsten carbide.

[0053] In the phase diagram from FIG. 1 (i.e., for a chromium content of Cr/(Fe+Ni Cr) of 2.2 wt %), at 1000° C., approximately between carbon contents of 5.565 to 5.64 wt %, the region 10 (“fcc+WC”) is apparent, which is the target range when producing the cobalt-free, tungsten carbide-based cemented carbide material, this being a region in which tungsten carbide grains and metallic binder are present without formation of η-phase (as at a lower carbon content, see region “fcc+WC+η”) and without formation of mixed carbide precipitates (as at higher carbon content, see region “fcc+WC+M.sub.7C.sub.3”). For a chromium content in relation to the total amount of iron, nickel and chromium of 2.2 wt %, as can be seen in FIG. 1, the carbon content when producing the cemented carbide material must already be held within relatively narrow tolerances in order to avoid precipitates. This, however, is still possible at acceptable cost and complexity.

[0054] As is evident from a comparison with the phase diagram represented in FIG. 2, for a chromium content of Cr/(Fe+Ni+Cr)=2.6 wt %, however, there is a sharp decrease in the width of the desired region 10 (“fcc+WC”) with increasing chromium content. As is evident in FIG. 3, the width of the region 10 for a chromium content of Cr/(Fe+Ni+Cr) of 3.0 wt % is now very narrow. In the phase diagram in FIG. 3, the region extends, at 1000° C., only between carbon contents of around 5.565 wt % to around 5.605 wt %. In other words, as the chromium content goes up, there is a rapid increase in the risk of unwanted mixed carbide precipitates or η-phase precipitates if the process atmosphere and therefore the carbon balance cannot be held within narrow tolerances.

[0055] Depending on the intended sector of use, the cobalt-free, tungsten carbide-based cemented carbide material may have a mean tungsten carbide particle size of 0.05-12 μm, preferably of 0.1-6 μm. The mean particle size of the tungsten carbide grains in the cemented carbide material may be determined using the equivalent circle diameter (ECD) method from EBSD (electron backscatter diffraction) images. This method is described for example in “Development of a quantitative method for grain size measurement using EBSD”; Master of Science Thesis, Stockholm 2012, by Frederik Josefsson.

[0056] The cobalt-free, tungsten carbide-based cemented carbide material of the embodiment was produced by powder metallurgy using WC powder having a particle size (FSSS, Fisher sieve sizes) of 0.6 μm or 1.2 μm or 1.95 μm, respectively, for the cemented carbide materials having the different grain sizes; Fe powder with an FSSS particle size of 2.3 μm, Ni powder with an FSSS particle size of 2.5 μm, Cr.sub.3C.sub.2 powder with an FSSS particle size of 1.5 μm, Mo.sub.2C powder with an FSSS particle size of 1.35 μm, and VC powder with an FSSS particle size of 1 μm. For the comparative examples, Co powder with an FSSS particle size of 0.9 μm was additionally employed. The materials were produced by mixing the respective starting powders with a solvent in a ball mill or attritor and then subjecting the mixture to spray drying in the customary way. The resulting granules were pressed and brought to the desired shape, and were subsequently sintered conventionally to give the cemented carbide material. In the production of the cemented carbide material by powder metallurgy, chromium may be added, for example, as the pure metal or in the form of Cr.sub.3C.sub.2 or Cr.sub.2N powder. Mo may be added preferably in the form of Mo.sub.2C powder, although, for example, its addition in the form of pure metal or, for example, (W, Mo)C mixed carbide is also possible. Fe, Ni and Cr may be added either individually or in prealloyed form.

Inventive and Comparative Examples

[0057] Cobalt-free, tungsten carbide-based cemented carbide materials of the invention and comparative examples were produced by the process described above.

[0058] The composition of the cemented carbide materials produced is summarized in table 1 below.

TABLE-US-00001 TABLE 1 WC grain Additives size WC Co Fe Ni Fe/(Fe + Ni) Cr V Mo Type [μm] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] [wt %] A 0.5-0.8 Bal.* 10 0 0 — 0.50 0.20 0.0 B 0.5-0.8 Bal. 0 6.88 2.29 0.75 0 0 0 C 0.5-0.8 Bal. 0 7.30 1.83 0.80 0 0 0 D 0.5-0.8 Bal. 0 7.72 1.36 0.85 0 0 0 E 0.5-0.8 Bal. 0 8.13 0.90 0.90 0 0 0 F 0.5-0.8 Bal. 0 6.91 2.30 0.75 0.26 0 0 G 0.5-0.8 Bal. 0 7.33 1.83 0.80 0.23 0 0 H 0.5-0.8 Bal. 0 7.74 1.37 0.85 0.20 0 0 I 0.5-0.8 Bal. 0 8.15 0.91 0.90 0.20 0 0 J 0.5-0.8 Bal. 0 7.76 1.37 0.85 0.20 0 0.47 K 0.5-0.8 Bal. 0 7.75 1.37 0.85 0.29 0 0 L 0.8-1.3 Bal. 20 0 0 — 0 0 0 M 0.8-1.3 Bal. 0 15.7 2.8 0.85 0.41 0 0 N 0.2-0.5 Bal. 6.5 0 0 — 0.30 0.30 0 O 0.2-0.5 Bal. 8 0 0 — 0.50 0.20 0 P 0.2-0.5 Bal. 0 5.01 0.89 0.85 0.13 0 0 Q 0.2-0.5 Bal. 0 5.01 0.89 0.85 0.13 0.06 0 *Bal. = Balance

[0059] The assignment as inventive or comparative examples is summarized in table 2 below. For the comparative examples, the last column indicates the reason why these are comparative examples.

TABLE-US-00002 TABLE 2 Inventive/ comparative Type Microstructure example Reason A very fine Comparative example Co-based B very fine Comparative example Cr-free C very fine Comparative example Cr-free D very fine Comparative example Cr-free E very fine Comparative example Cr-free F very fine Inventive example G very fine Inventive example H very fine Inventive example I very fine Inventive example J very fine Inventive example K very fine Comparative example excessive Cr content L fine Comparative example Co-based M fine Inventive example N ultrafine Comparative example Co-based O ultrafine Comparative example Co-based P ultrafine Inventive example Q ultrafine Inventive example

[0060] The cemented carbide materials produced for the inventive and comparative examples were each investigated for the mean particle size. Additionally determined on the cemented carbide materials produced were the Vickers hardness HV10, the fracture toughness K.sub.Ic, and the flexural strength FS.

[0061] The Vickers hardness HV10 here was determined according to ISO 3878:1991 (“Hardmetals—Vickers hardness test”). The fracture toughness K.sub.Ic in MPa.Math.m.sup.1/2 was determined according to ISO 28079:2009 with a test load (indentation load) of 10 kgf (corresponding to 98.0665 N). The flexural strength FS was determined according to standard ISO 3327:2009 on a test article of cylindrical cross section (form C).

[0062] Additionally, corrosion tests were carried out and the plastic deformation at elevated temperatures was investigated. The corrosion resistance and the creep resistance were evaluated qualitatively. Optical micrographs of the types were prepared, and some of them can be seen in FIG. 4 to FIG. 12. The optical micrographs were each recorded at 1500-fold magnification, or at 500-fold magnification in the case of FIG. 10. For the optical micrographs, the samples were each pretreated in the usual way by etching, with etching taking place for two minutes in each case except for the micrograph of FIG. 10. For the micrograph of FIG. 10, instead, etching took place only for 10 seconds, in order to provide better visualization of chromium carbide precipitates.

[0063] The results of the measurements are summarized in table 3 below.

TABLE-US-00003 TABLE 3 WC particle Hard- size ness K.sub.lc FS Corrosion Creep Type [μm] [HV10] [MPa .Math. m.sup.1/2] [MPa] resistance resistance A 0.5-0.8 1680 9.4 3700 good good B 0.5-0.8 1520 11.5 3225 poor poor C 0.5-0.8 1540 12.0 3450 poor poor D 0.5-0.8 1590 10.8 3540 very poor very poor E 0.5-0.8 1630 9.6 3210 very poor very poor F 0.5-0.8 1580 10.7 3430 moderate- moderate- good good G 0.5-0.8 1560 10.8 3680 moderate moderate H 0.5-0.8 1600 10.7 3850 moderate moderate I 0.5-0.8 1650 9.5 3450 poor- poor- moderate moderate J 0.5-0.8 1600 10.5 3800 moderate moderate K 0.5-0.8 1610 10.4 2800 moderate moderate L 0.8-1.3 1070 18.0 3400 poor poor M 0.8-1.3 1120 17.8 3300 moderate moderate N 0.2-0.5 2030 7.2 3800 good good O 0.2-0.5 1880 7.5 4300 good good P 0.2-0.5 1910 8.2 4000 moderate moderate Q 0.2-0.5 1970 7.6 3700 moderate moderate

[0064] From table 3 it is apparent that the conventional cobalt-containing, tungsten carbide-based cemented carbide material of type A, which as well as cobalt also contains chromium and vanadium, exhibits good results overall in terms of hardness, fracture toughness, flexural strength, corrosion resistance and creep resistance.

[0065] The conventional cobalt-containing cemented carbide materials of types N and O as well, which likewise contain chromium and vanadium as well as cobalt, exhibit both good corrosion resistance and good creep resistance. On account of their smaller mean particle size and their lower fraction of metallic binder, these types N and O do exhibit greater hardness and higher flexural strength, but also a fracture toughness which is significantly reduced relative to type A.

[0066] Type L, likewise serving as a comparative example of a cobalt-containing, tungsten carbide-based cemented carbide material, and containing neither chromium nor vanadium further to the cobalt, does exhibit a very high fracture toughness, by virtue of its relatively high metallic binder content; however, the corrosion resistance and the creep resistance are each poor.

[0067] The comparative examples of types B, C, D and E are each cobalt-free, tungsten carbide-based cemented carbide materials in which the metallic binder in each case is an iron-nickel-based alloy containing no chromium. Types B, C, D and E differ in the iron-nickel ratio of the metallic binder. The total amount (Fe+Ni) of iron and nickel in these cases was adapted such that the resulting volume of the binder corresponds substantially to that of a conventional cobalt-containing, tungsten carbide-based cemented carbide material with 10 wt % of cobalt binder. From table 3 it is apparent that the comparative examples of types B, C, D and E do exhibit acceptable results for the hardness HV10, the fracture toughness K.sub.Ic and the flexural strength FS, and yet the corrosion resistance and the creep resistance are in each case poor or even very poor. Corrosion resistance and creep resistance deteriorate with increasing percentage iron fraction of the metallic binder.

[0068] The inventive examples of cobalt-free, tungsten carbide-based cemented carbide materials of types F, G, H and I differ from the comparative examples of types B, C, D and E essentially in the addition of small amounts of chromium. As is apparent from table 3, the addition of chromium has a slight tendency to increase the hardness HV10 and a slight tendency to reduce the fracture toughness K.sub.Ic. The addition of chromium is beneficial to the flexural strength FS. As can likewise be seen, the addition of chromium significantly improves the corrosion resistance and the creep resistance. Good values are achieved overall for the hardness HV10, the fracture toughness K.sub.Ic and the flexural strength BBF. Overall, relative to the comparative examples of types B, C, D and E, distinct improvements are also achieved in the corrosion resistance and the creep resistance. For the range of Fe/(Fe+Ni) up to 0.85 wt %, physical properties are achieved overall which, while not entirely reaching the values for conventional cobalt-containing, tungsten carbide-based cemented carbide material (such as that of type A, for example), nevertheless come very close to them overall. By comparison with this, for the range Fe/(Fe+Ni)>0.85 (see type I), the corrosion resistance achieved is somewhat poorer and the creep resistance achieved is somewhat poorer, but may well be sufficient for some applications.

[0069] As is apparent from a comparison of the comparative example of type K with the inventive example of type H, an increase in the amount of chromium added does not directly have an adverse effect on the hardness HV10 and the fracture toughness K.sub.Ic, but nor is any further improvement observable in the corrosion resistance and the creep resistance. The increased chromium addition does, however, lead to a significant deterioration in the flexural strength FS. In the optical micrograph of type K in FIG. 10, for which the type K was incipiently etched for only 10 seconds for pretreatment, it is evident that mixed carbide precipitates have formed, and are held responsible for the significant deterioration in the flexural strength FS.

[0070] As is evident from a comparison of the inventive examples of types H and J, on the other hand, the addition of molybdenum has no adverse effect on the achievable physical properties.

[0071] In the case of a comparison of the inventive example of type M with the comparative example of the cobalt-containing type L, it is evident that even with fractions of the metallic binder in the cemented carbide material that are higher overall, it is possible to achieve acceptable physical properties in comparison to conventional cobalt-containing cemented carbide materials.

[0072] As evident from a comparison with type P, an acceptable corrosion resistance and an acceptable creep resistance are achieved even when the content of the metallic binder is lower overall and the mean particle size of the tungsten carbide grains is reduced. Because of the lower mean particle size and the lower fraction of the metallic binder, on the one hand a higher hardness is achieved and an increased flexural strength is achieved because of the lower mean particle size, while on the other hand there is also a drop in the fracture toughness K.sub.Ic in accordance with expectation. Overall, however, the physical properties achieved are entirely acceptable by comparison with conventional cobalt-containing, tungsten carbide-based cemented carbide materials of types N and O.

[0073] From a comparison of types P and Q it is evident that the addition of small amounts of vanadium leads to a slight increase in the hardness, but is accompanied by a reduction in the fracture toughness and in the capacity for flexion before breaking.