CUTTING INSERTS FOR EARTH-BORING BITS

BACKGROUND OF THE TECHNOLOGY

1. Field of the Technology

The present disclosure relates to cutting inserts adapted for use in earth-boring bits and in other articles of manufacture.

2. Description of the Background of the Technology

Cemented carbides are composites including a discontinuous hard phase dispersed in a continuous relatively soft metallic binder phase. The dispersed (discontinuous) phase typically comprises transition metal carbide, nitride, silicide, and/or oxide, wherein the transition metal is selected from, for example, titanium, vanadium, chromium, zirconium, hafnium, molybdenum, niobium, tantalum, and tungsten. The binder phase typically comprises at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. Alloying elements such as, for example, chromium, molybdenum, boron, tungsten, tantalum, titanium, and niobium may be included in the binder to enhance certain properties of the composite material. The binder phase binds or “cements” the dispersed hard grains together, and the composite exhibits an advantageous combination of the physical properties of the discontinuous and continuous phases. Although the discontinuous hard phase of such composites may not include metal carbides, the commercially available versions typically include carbides as the discontinuous hard phase. Therefore, the composites are commonly referred to as “cemented carbides” even if carbides are absent or only constitute a portion of the discontinuous hard phase. Accordingly, references herein to “cemented carbides”, both in the present description and the claims, refer to such materials whether or not they include metallic carbides.

Numerous cemented carbide types or “grades” are produced by varying parameters that may include the composition of the materials in the dispersed and/or continuous phases, the average size of the dispersed phase regions, and the volume fractions of the discontinuous and continuous phases. Cemented carbides including a dispersed tungsten carbide phase and a cobalt or cobalt alloy binder phase are the most commercially important of the commonly available cemented carbide grades. Conventional cemented carbide grades are available as powders (referred to herein as “cemented carbide powders”), which may be processed to a final form using, for example, conventional press-and-sinter techniques.

Cemented carbide grades including a discontinuous tungsten carbide phase and a continuous cobalt binder phase exhibit advantageous combinations of ultimate tensile strength, fracture toughness, and wear resistance. As is known in the art, “ultimate tensile strength” is the stress at which a material ruptures or fails. “Fracture toughness” refers to the ability of a material to absorb energy and deform plastically before fracturing. “Toughness” is proportional to the area under the stress-strain curve from the origin to the breaking point. See MCGRAW-HILL DICTIONARY OF SCIENTIFIC AND TECHNICAL TERMS (5^thed. 1994). “Wear resistance” refers to the ability of a material to withstand damage to its surface. Wear generally involves progressive loss of material from an article due to relative motion between the article and a contacting surface or substance. See METALS HANDBOOK DESK EDITION (2d ed. 1998). Cemented carbides find extensive use in applications requiring substantial strength and toughness and high wear resistance. Such applications include, for example, metal cutting and metal forming applications, earth-boring and rock cutting applications, and use in machinery wear parts.

The strength, toughness, and wear resistance of a cemented carbide are related to the average size of the regions of dispersed hard phase and the volume (or weight) fraction of the binder phase present in the composite. Generally, increasing the average grain size of the dispersed hard regions and/or the volume fraction of the binder phase in a conventional cemented carbide grade increases the fracture toughness of the composite. However, this increase in toughness is generally accompanied by decreased wear resistance. Metallurgists formulating cemented carbides, therefore, are continually challenged to develop grades exhibiting both high wear resistance and high fracture toughness, and which are otherwise suitable for use in demanding applications.

In many instances, cemented carbide parts are produced as individual articles using conventional powder metallurgy press-and-sinter techniques. The press-and-sinter manufacturing process typically involves pressing or otherwise consolidating a portion of a cemented carbide powder in a mold to provide an unsintered, or “green”, compact of defined shape and size. If additional shape features are required in the cemented carbide part that cannot be achieved readily by consolidating the powder, the green compact is machined prior to sintering. This machining step is referred to as “green shaping”. If additional compact strength is needed for the green shaping process, the green compact can be presintered before green shaping. Presintering occurs at a temperature lower than the final sintering temperature and provides what is referred to as a “brown” compact. The green shaping operation is followed by the high temperature sintering step. Sintering densifies the material to near theoretical full density to produce a cemented carbide composite. Sintering also develops desired strength and hardness in the composite material.

Rotary cone earth-boring bits and fixed cutter earth-boring bits are employed for oil and natural gas exploration, mining, excavation, and the like. Rotary cone bits typically comprise a steel body onto which cutting inserts, which may be made from cemented carbide or another material, are attached. Referring to FIG. 1, a typical rotary cone bit 10 adapted for earth-boring applications includes a steel body 12 and two or three interlocking rotary cones 13 that are rotatably attached to the body 12. A number of cutting inserts 14 are attached to each rotary cone by, for example, mechanical means, adhesive, or brazing. The cutting inserts, which also may be referred to as “cutting elements”, may be made from cemented carbide or another material. FIG. 2 depicts a number of cemented carbide cutting inserts 22 attached to a surface 24 of an insert holder portion of a fixed cutter earth-boring bit.

Conventional cemented carbide cutting inserts configured for use with earth-boring bits are commonly based on pure tungsten carbide (WC) as the dispersed hard phase and pure cobalt (Co) as the continuous binder phase. While WC—Co cemented carbide cutting inserts provide advantages relative to materials previously used in cutting inserts for rotary cone earth-boring bits, WC—Co inserts can suffer from premature abrasion and wear. Premature wear may necessitate replacement of one or more worn cutting inserts or an entire rotary cone or fixed cutter earth-boring bit, which requires removing the drill string from the borehole. This can significantly slow and increase the cost of the drilling process.

Accordingly, it would be advantageous to develop an improved cemented carbide material for use in cutting inserts for rotary cone, fixed cutter, and other earth-boring bits that exhibits advantageous abrasion resistance and wear life compared with conventional WC—Co cemented carbides, while not significantly compromising cutting insert strength and toughness. More generally, it would be advantageous to provide a novel cemented carbide material for uses including those wherein high abrasion resistance and wear life are desired, and wherein strength and toughness also are important.

SUMMARY

One non-limiting aspect of the present disclosure is directed to an earth-boring bit cutting insert comprising a cemented carbide material. In certain non-limiting embodiments according to the present disclosure, the cemented carbide material comprises a plurality of tungsten carbide grains, and a plurality of cubic carbide grains comprising at least one of titanium carbide, vanadium carbide, zirconium carbide, hafnium carbide, niobium carbide, tantalum carbide, and solid solutions thereof. The cemented carbide material includes a binder comprising at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy.

Another non-limiting aspect of the present disclosure is directed to an earth-boring bit cutting insert comprising a hybrid cemented carbide material. The hybrid cemented carbide material comprises a plurality of first cemented carbide regions comprising tungsten carbide grains and a cobalt binder. The plurality of first cemented carbide regions comprise a dispersed phase. The hybrid cemented carbide material also comprises a second, continuous cemented carbide region comprising second cemented carbide grains in a second region binder. In non-limiting embodiments, the second cemented carbide grains comprise tungsten carbide and at least one of titanium carbide, vanadium carbide, zirconium carbide, hafnium carbide, niobium carbide, tantalum carbide, and solid solutions thereof. The second region binder comprises at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. The plurality of first cemented carbide regions are dispersed in the seconded continuous cemented carbide region. The earth-boring bit cutting inserts comprising a hybrid cemented carbide material may be adapted for use on at least one of a rotary cone earth-boring bit and a fixed cutter earth-boring bit.

Yet another non-limiting aspect of the present disclosure is directed to an earth-boring bit. An earth-boring bit according to certain non-limiting embodiments of the present disclosure comprises an earth-boring bit body and at least one earth-boring bit cutting insert. The at least one earth-boring bit cutting insert comprises a cemented carbide material. In certain non-limiting embodiments according to the present disclosure, the cemented carbide material of the at least one cutting insert of the earth-boring bit comprises a plurality of tungsten carbide grains and a plurality of cubic carbide grains. The plurality of cubic grains comprises at least one of titanium carbide, vanadium carbide, zirconium carbide, hafnium carbide, niobium carbide, tantalum carbide, and solid solutions thereof. The cemented carbide material of the at least one earth-boring bit cutting insert includes a binder comprising at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of methods and articles of manufacture described herein may be better understood by reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a rotary cone earth-boring bit comprising a steel body and conventional WC—Co cemented carbide cutting inserts mounted on the rotary cones;

FIG. 2 is a perspective view of a cutting insert holder portion of a fixed cutter earth-boring bit with attached conventional WC—Co cemented carbide cutting inserts;

FIG. 3A is a micrograph showing the microstructure of a prior art Grade H-25 cemented carbide material used for earth-boring bit cutting inserts and comprising tungsten carbide hard particles in a cobalt binder;

FIG. 3B is a micrograph showing the microstructure of a prior art Grade 231 cemented carbide material used for earth-boring cutting inserts and comprising tungsten carbide hard particles in a cobalt binder;

FIG. 3C is a micrograph showing the microstructure of a prior art Grade 45B cemented carbide material used for earth-boring bit cutting inserts and comprising tungsten carbide hard particles in a cobalt binder;

FIG. 4 is a schematic representation of the microstructure of a non-limiting embodiment of a cemented carbide material according to the present disclosure useful for earth-boring cutting inserts and comprising a plurality of tungsten carbide grains, a plurality of cubic carbide grains, and a metallic binder;

FIG. 5 is a schematic representation of the microstructure of a non-limiting embodiment of hybrid cemented carbide material according to the present disclosure useful for earth-boring cutting inserts;

FIG. 6 is a graphical depiction of a step in a method for determining the contiguity ratio of a composite material, such as a cemented carbide material, comprising a dispersed phase and a continuous matrix phase;

FIG. 7 is a schematic representation of a rotary cone earth-boring bit according to the present disclosure, including a plurality of cutting inserts comprising cubic carbides;

FIG. 8 is a micrograph of a non-limiting embodiment of a cemented carbide material according to the present disclosure useful for earth-boring cutting inserts and comprising cubic carbides grains consisting of a solid solution of titanium carbide, tantalum carbide, and niobium carbide;

FIG. 9 is a micrograph of a non-limiting embodiment of a cemented carbide material according to the present disclosure useful for earth-boring cutting inserts and comprising cubic carbides grains consisting of a solid solution of tantalum carbide and niobium carbide;

FIG. 10 is a micrograph of a non-limiting embodiment of a hybrid cemented carbide material according to the present disclosure useful for earth-boring cutting inserts;

FIG. 11 is a schematic representation of an apparatus employed for measuring the wear resistance of cemented carbides according to ASTM B611 used in Example 4 of the following disclosure; and

FIG. 12 is graph plotting wear number for several cemented carbide materials evaluated for wear resistance in Example 4 of the following disclosure.

The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of certain non-limiting embodiments according to the present disclosure.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments, other than in the operating examples or where otherwise indicated, all numbers expressing quantities or characteristics are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description are approximations that may vary depending on the desired properties one seeks to obtain in the materials and articles according to the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each such numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

As used herein, and unless specified otherwise herein, the terms “cemented carbide”, “cemented carbide material”, and “cemented carbide composite” refer to a sintered material.

While not meant to be limiting, the cemented carbide materials according to the present disclosure may be prepared using conventional techniques for preparing cemented carbide materials. One such conventional technique known as the “press-and-sinter” technique involves pressing a portion of a single or mixture of precursor metallurgical powders to form a green compact, followed by sintering the compact to densify the compact and metallurgically bind the powder particles together. The details of press-and-sinter techniques applied in the production of cemented carbide materials are well known to persons having ordinary skill in the art and, therefore, further description of such details need not be provided herein.

As previously indicated, cemented carbide cutting inserts used with earth-boring bits typically have been based on pure WC as the hard, dispersed, discontinuous phase, and substantially pure Co as the continuous binder phase. WC—Co cutting inserts, however, may suffer from premature abrasion and wear. While not wishing to be held to any particular theory, the present inventors believe that premature wear of WC—Co cutting inserts applied in earth-boring operations results from at least two factors. A first factor is the generally angular morphology of WC grains in the WC—Co material. A second factor is the relative softness of WC, as compared with other transition metal carbides. The photomicrographs of FIGS. 3A through 3C illustrate typical microstructures of WC—Co based cemented carbide materials employed in cutting inserts for earth-boring applications. The WC—Co cemented carbide material shown in FIG. 3A was formed using a press-and-sinter technique from Grade H-25 cemented carbide powder, and includes 75 percent by weight WC particles (also referred to as “grains”) having an average grain size of 4 to 6 μm, and 25 percent by weight of cobalt binder. The WC—Co cemented carbide material shown in FIG. 3B was formed using a press-and-sinter technique from Grade 231 cemented carbide powder, and includes 90 percent by weight WC grains having an average grain size of 4 to 6 μm, and 10 percent by weight of cobalt binder. The WC—Co cemented carbide material shown in FIG. 3C was formed using a press-and-sinter technique from Grade 45B cemented carbide powder, and includes 84 percent by weight WC grains having an average grain size of 4 to 6 μm, and 84 percent by weight of cobalt binder. The three grades of WC—Co powder used to make the materials shown in FIGS. 3A-3C are available from ATI Firth Sterling, Madison, Ala. With reference to FIGS. 3A-3C, the WC grains (dark gray regions) exhibit an angular shape, with many of the WC grains including sharp, jagged edges. The present inventors have observed that as WC—Co material wears and abrades and the binder material wears away (as occurs during earth-boring operations), sharp edges of WC grains tend to chip and break readily, leading to premature wear and micro-crack formation in the material.

An aspect of the present disclosure is directed to a cemented carbide material useful for earth-boring bit cutting inserts in which, in a non-limiting embodiment, up to 50% by weight of the cemented carbide material comprises grains of cubic carbides. In another non-limiting embodiment directed to a cemented carbide material useful for earth-boring bit cutting inserts, up to 30% by weight of the cemented carbide material comprises grains of cubic carbides. Cubic carbides used in accordance with non-limiting embodiments of the present disclosure include transition metal carbides from Groups IVB and VB of the Periodic Table of the Elements. These transition metal cubic carbides include titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, and tantalum carbide. It has been observed that following pressing and sintering of cemented carbide materials according to the present disclosure, grains of the transition metal cubic carbides and their solid solutions within the material exhibit a relatively rounded grain shape or grain structure. As used herein, the term “grain” refers to individual crystallites of transition metal carbides. As used herein the phrases “angular grains” and “grains with angular features”, and variants thereof, refer to grains that possess well-defined edges and sharp corners where the corners form acute through obtuse angles when the material is viewed in a micrograph. As used herein, the phrases “rounded grains”, “rounded grain shapes”, “rounded grain structures”, and variants thereof, refer to grains having smooth edges with a degree of curvature when the material is viewed in a micrograph.

The present inventors have concluded that formulating a cemented carbide material with a significant proportion of transition metal carbide grains having a relatively rounded morphology, rather than an angular morphology, will significantly enhance the wear resistance of the cemented carbide material. The present inventors conclude that such a material will improve the wear resistance characteristics of an earth-boring cutting insert, without significantly compromising other important properties of the earth-boring bit cutting insert.

Referring now to the schematic representation of FIG. 4, in a non-limiting embodiment according to the present disclosure, a novel cemented carbide material 40 useful for an earth-boring bit cutting insert comprises a plurality of tungsten carbide grains 42. The cemented carbide material 40 further comprises a plurality of cubic carbide grains 44 comprising transition metal cubic carbide. In a non-limiting embodiment, the plurality of cubic carbide grains comprises grains of at least one carbide of a transition metal selected from Group IVB and Group VB of the Periodic Table of the Elements. In another non-limiting embodiment, the plurality of cubic carbide grains comprise at least one of titanium carbide, vanadium carbide, zirconium carbide, hafnium carbide, niobium carbide, tantalum carbide, and solid solutions thereof. In other non-limiting embodiments, the plurality of cubic carbide grains comprise titanium carbide, or tantalum carbide, or niobium carbide, or grains of a solid solution of titanium carbide, tantalum carbide, and niobium carbide. After the step of sintering to produce the cemented carbide material, the cubic carbide grains in the cemented carbide material generally exhibit a more rounded shape than the tungsten carbide grains in the material.

Still referring to FIG. 4, the cemented carbide material for earth-boring bit cutting inserts according to the present disclosure 40 includes a binder 46 (which also may be referred to as a binder phase). In a non-limiting embodiment, the binder 46 comprises at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. In another non-limiting embodiment of a cemented carbide material according to the present disclosure, the binder 46 comprises cobalt. In still other non-limiting embodiments, the binder 46 includes at least one additive selected from chromium, ruthenium, rhenium, molybdenum, boron, tungsten, tantalum, titanium, niobium, silicon, aluminum, copper, and manganese. In certain non-limiting embodiments, the binder 46 of the cemented carbide material 40 may include up to a total of 20 weight percent of the additives, based on the total weight of the binder 46. In other non-limiting embodiments, the binder 46 of the cemented carbide material 40 may include a total of up to 15 weight percent, up to 10 weight percent, or up to 5 weight percent of the additives, based on the total weight of the binder 46.

In a non-limiting embodiment of a cemented carbide material according to the present disclosure, the cemented carbide material comprises, in weight percent based on total material weight, 1 to 30% of grains of cubic carbide, 2 to 35% of binder, and the balance being grains of tungsten carbide. In another non-limiting embodiment of a cemented carbide material according to the present disclosure, the cemented carbide material comprises, in weight percent based on total material weight, 1 to 50% of grains of cubic carbide, 2 to 35% of binder, and the balance being grains of tungsten carbide.

Transition metal cubic carbides exhibit a large solubility for one another, and only a slight solubility for tungsten carbide. Therefore, after a step of sintering to produce cemented carbide materials according to the present disclosure, solid solutions of cubic carbides can be formed, which may be referred to as “complex carbides”. In various non-limiting embodiments, these complex carbides, or carbide solid solutions, may exhibit a rounded morphology. Tungsten carbide has no solubility for any of the cubic carbides and, therefore, after sintering to produce cemented carbide materials according to the present disclosure, the tungsten carbide grains generally remain as angular grains with sharp corners.

Certain embodiments according to the present invention include earth-boring bit cutting inserts comprising hybrid cemented carbide material (or simply “hybrid cemented carbides”). Whereas a cemented carbide is a composite material typically comprising a discontinuous phase of transition metal carbide dispersed throughout a continuous binder phase, a hybrid cemented carbide comprises at least one discontinuous phase of a cemented carbide grade dispersed throughout a cemented carbide continuous phase, thereby forming a composite of cemented carbides. Hybrid cemented carbides, which are materials well known in the art, are described, for example, in U.S. Pat. No. 7,384,443 (“the U.S. '443 patent”), which is incorporated by reference herein in its entirety.

Referring to the schematic representation shown in FIG. 5, in a non-limiting embodiment of a hybrid cemented carbide 50 according to the present disclosure useful for a cutting insert, each of a plurality of first cemented carbide regions 52 comprises tungsten carbide grains in a first region binder comprising cobalt. The continuous second cemented carbide region 54 comprises second cemented carbide grains in a second region binder. The second cemented carbide grains comprise tungsten carbide grains and grains of at least one of titanium carbide, vanadium carbide, zirconium carbide, hafnium carbide, niobium carbide, tantalum carbide, and solid solutions thereof. The second region binder comprises at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. The plurality of first cemented carbide regions 52 are dispersed in the continuous second cemented carbide region 54.

It is recognized that the scope of the present disclosure includes hybrid cemented carbides wherein the compositions of first regions and second regions are reversed from that described above. That is, in a non-limiting embodiment, the first regions of cemented carbide may comprise tungsten carbide together with cubic carbides and a binder comprising at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy, and the first regions are dispersed in a continuous phase of a second region cemented carbide comprising tungsten carbide grains in a cobalt binder.

Certain embodiments of the method for producing hybrid cemented carbides according to the U.S. '443 patent provide for the formation of such materials wherein the dispersed cemented carbide phase has a relatively low contiguity ratio. The degree of dispersed phase contiguity in a composite structure may be characterized as the contiguity ratio, C_t. As is known to those having ordinary skill, C_tmay be determined using a quantitative metallography technique described in Gurland, “Application of Quantitative Microscopy to Cemented Carbides”, Practical Applications of Quantitative Metalloaraphy, ASTM STP 839, J. L. McCall and J. H. Steale, Jr., Eds., American Society for Testing and Materials, Philadelphia (1984) pp. 65-83, hereby incorporated by reference. The technique consists of determining the number of intersections that randomly oriented lines of known length, placed on the microstructure as a photomicrograph of the material, make with specific structural features. The total number of intersections in the photomicrograph made by the lines with dispersed phase/dispersed phase intersections are counted and are referred to as N_Lαα. The total number of intersections in the photomicrograph made by the lines with dispersed phase/continuous phase interfaces also are counted and are referred to as N_Lαβ. FIG. 6 schematically illustrates the procedure by which the values for N_Lαα and N_Lαβ are obtained. In FIG. 6, 60 generally designates a composite including the dispersed phase 62 of a phase in a continuous phase 64 of β phase. The contiguity ratio C_tis calculated by the equation C_t=2 N_Lαα/(N_Lαβ+2 N_Lαα). The method described in Gurland is extended to measuring the contiguity ratio of hybrid cemented carbide composites in the U.S. '443 patent, for example.

The contiguity ratio is a measure of the average fraction of the surface area of dispersed phase regions in contact with other dispersed first phase regions, i.e., contiguous dispersed phase regions. The ratio may vary from 0 to 1 as the distribution of the dispersed regions changes from completely dispersed to a fully agglomerated structure. The contiguity ratio describes the degree of continuity of dispersed phase irrespective of the volume fraction or size of the dispersed phase regions. However, typically, for higher volume fractions of the dispersed phase, the contiguity ratio of the dispersed phase will also likely be relatively high.

In the case of hybrid cemented carbides, when the dispersed phase of cemented carbide has a higher hardness than the continuous phase of cemented carbide, lower contiguity ratios for the cemented carbide dispersed phase reflect a smaller likelihood that a crack will propagate through any contiguous dispersed phase regions. This cracking process may be a repetitive one, with cumulative effects resulting in a reduction in the overall toughness of the hybrid cemented carbide article, which may be present in, for example, a cutting insert for an earth-boring bit. As mentioned above, replacing a cutting insert or an entire earth-boring bit may be both time-consuming and costly.

In certain embodiments, hybrid cemented carbides according to the present disclosure may comprise between about 2 to about 40 vol. % of the cemented carbide grade of the first region or dispersed phase. In other embodiments, the hybrid cemented carbides may comprise between about 2 to about 30 vol. % of the cemented carbide grade of the second region or continuous phase. In still further applications, it may be desirable to include between 6 and 25 volume % of the cemented carbide of the first region or dispersed phase in the hybrid cemented carbide.

The U.S. '443 patent discloses a method of producing hybrid cemented carbides with improved properties. As is known to those having ordinary skill, the method of producing a hybrid cemented carbide typically includes blending at least one of partially and fully sintered granules of the dispersed cemented carbide grade (i.e., the first region cemented carbide) with at least one of green and unsintered granules of the continuous cemented carbide grade (i.e., the second region cemented carbide). The blend is then consolidated, and subsequently is sintered using conventional means. Partial or full sintering of the granules of the dispersed phase results in strengthening of the granules (as compared to “green” granules). In turn, the strengthened granules of the dispersed phase will have an increased resistance to collapse during the step of consolidating the blend. The granules of the dispersed phase may be partially or fully sintered at temperatures ranging from about 400° C. to about 1300° C., depending on the desired strength of the dispersed phase. The granules may be sintered by a variety of means, such as, but not limited to, hydrogen sintering and vacuum sintering. Sintering of the granules may remove lubricant, reduce oxides, and densify and develop the microstructure of the granules. Partially or fully sintering the dispersed phase granules prior to blending results in a reduction in the collapse of the dispersed phase during consolidation.

In addition to shape differences between WC grains and grains of other transition metal carbides such as, for example, titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), zirconium carbide (ZrC), hafnium carbide (HfC), and vanadium carbide (VC), there are significant differences in the melting points and microhardness of the different carbides, as shown in Table 1.

TABLE 1

Transition Metal Carbide
Melting Point (° C.)
Microhardness (kg/mm²)

TiC
3,250
3,200

ZrC
3,175
2,600

HfC
3,900
3,400

VC
2,830
2,800

NbC
3,500
2,400

WC
2,630
2,300

As is observed in Table 1, TiC, TaC, NbC, ZrC, HfC, and VC have significantly higher melting points than WC, and are harder than WC. The present inventors believe that based on the higher hardness and more rounded morphology of grains of carbides of titanium, tantalum, niobium, zirconium, hafnium, and vanadium compared to tungsten carbide, the overall wear resistance of cemented carbide materials and articles, such as cutting inserts for earth-boring bits, according to the present disclosure will be significantly greater than for materials and articles, such as earth-boring bit cutting inserts, made from cemented carbide consisting of WC and Co. The improvement in wear resistance should result in an increase in service life for earth-boring bits including cutting inserts made from cemented carbide materials according to the present disclosure.

The addition of TiC to cemented carbide materials in certain embodiments according to the present disclosure will improve corrosion resistance, which, in turn, will help to avoid premature wear failures resulting from corrosion. The addition of TaC to cemented carbide materials in certain embodiments according to the present disclosure will improve elevated-temperature hardness as well as resistance to micro-crack formation during thermal cycling, which is a common failure mode in cemented carbide inserts employed in earth-boring applications.

Another aspect according to the present disclosure is directed to an article of manufacture wherein at least a portion of the article comprises or consists of one or more of the cemented carbide materials according to the present disclosure. The articles of manufacture include, but are not limited to, cutting inserts for earth-boring bits. Cutting inserts according the present disclosure include, for example, cutting inserts for rotary cone earth-boring bits, fixed cutter earth-boring bits, and other earth-boring bits. FIG. 7 is a schematic representation of a rotary cone earth-boring bit 70 according to the present disclosure. A rotary cone earth-boring bit 70 according to a non-limiting embodiment comprises a conventional earth-boring bit body 72 that includes a plurality of cutting inserts 74 fabricated according to embodiments of the present disclosure.

In addition, the advantageous combination of strength, fracture toughness, and abrasion/wear resistance of cemented carbide materials according to the present disclosure make the cemented carbide materials attractive for use on blade portions, cutting insert holder portions, and blade support portions of fixed cutter earth-boring bits. It also is believed that embodiments of cemented carbide materials according to the present disclosure can be used in cutting inserts and cutting tools for machining metals and metallic alloys, such as, but not limited to, titanium alloys, nickel-based superalloys, and other difficult-to-machine metallic alloys.

Example 1

The microstructure of a non-limiting embodiment of a sintered cemented carbide material according to the present disclosure is shown in the photomicrograph of FIG. 8. The cemented carbide material shown in FIG. 8 was prepared by forming a powder blend consisting of, in percent by weight, 75% WC powder, 8% TiC powder, 5% TaC powder, 5% NbC powder, and 7% Co powder. The blended powder was consolidated into a green compact. The green compact was sintered at 1420° C.

The cemented carbide shown in the micrograph of FIG. 8 exhibits grains of tungsten carbide, and rounded grains comprising titanium carbide, tantalum carbide, niobium carbide, and their solid solutions. It is anticipated that the presence of the rounded grains comprising cubic carbides will improve the wear resistance of cutting inserts for earth-boring bits, while not substantially affecting certain other important properties of the cutting inserts, thereby extending the service life of the cutting inserts.

Example 2

The microstructure of a non-limiting embodiment of a sintered cemented carbide material according to the present disclosure is shown in the photomicrograph of FIG. 9. The cemented carbide material shown in FIG. 9 was prepared by forming a powder blend consisting of, in percent by weight, 50% WC powder, 22% TaC powder, 20% NbC powder and 8% Co powder. The blended powder was consolidated into a green compact. The green compact was sintered at 1420° C.

The cemented carbide in the micrograph of FIG. 9 exhibits grains of tungsten carbide, and rounded grains comprising tantalum carbide, niobium carbide, and their solid solutions. It is anticipated that the presence of the rounded grains comprising cubic carbides will improve the wear resistance of cutting inserts for earth-boring bits, while not substantially affecting certain other important properties of the cutting inserts, thereby extending the service life of the cutting inserts.

Example 3

The microstructure of a non-limiting embodiment of a sintered hybrid cemented carbide material according to the present disclosure is shown in the photomicrograph of FIG. 10. Two separate metallurgical powder blends were prepared. The first metallurgical powder blend, used for the continuous, second cemented carbide region, was prepared by forming a powder blend consisting of, in percent by weight, 50% WC powder, 22% TaC powder, 20% NbC powder, and 8% Co powder. A second metallurgical powder blend to be used for the plurality of first cemented carbide regions, or dispersed phase, was prepared by blending, in percent by weight, 90% of WC powder and 10% of Co powder. In percent by weight, 85% of the first metallurgical powder blend was mixed with 15% of the second metallurgical powder blend. The mixed powder was consolidated and sintered at 1420° C. to form a sintered hybrid cemented carbide material.

In the non-limiting embodiment of FIG. 10, a hybrid cemented carbide material comprises a plurality of first cemented carbide regions (the lighter colored regions in the photomicrograph of FIG. 10) comprising tungsten carbide grains in a binder phase comprising cobalt, dispersed in a continuous second region (the darker region in the photomicrograph of FIG. 10) of a second cemented carbide comprising tungsten carbide grains and also grains of titanium carbide, tantalum carbide, niobium carbide, and their solid solutions. It is anticipated that the presence of the cubic carbides will improve the wear resistance of cutting inserts for earth-boring bits, while not substantially affecting certain other important properties of the cutting inserts, thereby extending the service life of the cutting inserts.

Example 4

A study was conducted to assess the effectiveness of cubic carbide addition to increase abrasion resistance of cemented carbides. The following cemented carbide materials having the indicated compositions were prepared from metallurgical powders using conventional press-and-sinter techniques:

Alloy A: Cemented carbide consisting of 10 weight percent cobalt and balance tungsten carbide. The material included a discontinuous phase of tungsten carbide in a continuous phase of cobalt. The grain size of the tungsten carbide was about 5 μm.

Alloy B: Cemented carbide consisting of 10.55 weight percent cobalt, 2.5 weight percent titanium carbide, 2.5 weight percent tantalum carbide, and balance tungsten carbide. The material included a discontinuous phase including grains of titanium carbide and tantalum carbide (both cubic carbides) and grains of tungsten carbide, in a continuous phase of cobalt. As in Alloy A, the tungsten carbide grain size was about 5 μm. The cobalt content in Alloy B was higher than in Alloy A to compensate for the change in the total volume fraction of the hard phases and thereby maintain a constant volume fraction of the binder (cobalt). Thus, Alloy B differs from Alloy A in the addition of cubic carbides.

Alloy C: Cemented carbide consisting of 10.75 weight percent cobalt, 5 weight percent titanium carbide, 5 weight percent tantalum carbide, and balance tungsten carbide. The material included a discontinuous phase including grains of titanium carbide, tantalum carbide, and tungsten carbide, in a continuous phase of cobalt. The tungsten carbide grain size remained the same (about 5 μm) as in Alloys A and B, and the cobalt content was selected to maintain a constant volume fraction of the binder relative to Alloys A and B. Alloy C differs from Alloy B in that it includes a higher volume fraction of cubic carbides.

Alloy D: Cemented carbide consisting of 11.1 weight percent cobalt, 10 weight percent titanium carbide, 10 weight percent tantalum carbide, and balance tungsten carbide. The material included a discontinuous phase including grains of titanium carbide, tantalum carbide, and tungsten carbide, in a continuous phase of cobalt. The tungsten carbide grain size remained the same (about 5 μm) as in Alloys A-C, and the cobalt content was selected to maintain a constant volume fraction of the binder relative to Alloys A-C. This alloy is similar to alloy C but contains a higher cubic carbide content.

Alloy E: Cemented carbide consisting of 10.55 weight percent cobalt, 5 weight percent tantalum carbide, and balance tungsten carbide. The material included a discontinuous phase including grains of tantalum carbide and grains of tungsten carbide, in a continuous phase of cobalt. The tungsten carbide grain size remained the same (about 5 μm) as in Alloys A-D. Alloy E is similar to Alloy B but all cubic carbide is present as tantalum carbide.

Alloy F: Cemented carbide consisting of 10.75 weight percent cobalt, 10 weight percent tantalum carbide, and balance tungsten carbide. The material included a discontinuous phase including grains of tantalum carbide and grains of tungsten carbide, in a continuous phase of cobalt. The tungsten carbide grain size remained the same (about 5 μm) as in Alloys A-E. Alloy F is similar to Alloy C but all cubic carbide is present as tantalum carbide.

The abrasion resistance of each of each of Alloys A-F was measured using the procedure described in ASTM B611-85 (2005) (“Standard Test Method for Abrasive Resistance of Cemented Carbides”). The test apparatus used in the wear resistance testing is shown schematically in FIG. 11. The test consisted of abrading a specimen of the test material using an aluminum oxide particle slurry. The slurry was abraded against a surface of the test specimen by a rotating steel wheel partially disposed in a bath of the slurry. As indicated in FIG. 11, the specimen was urged against the peripheral surface of the rotating wheel (and the slurry on that surface) using a weight and a pivot arrangement. The wheel included mixing vanes on both sides thereof to agitate the slurry during wheel rotation. The volume loss (cm³) experienced by the test specimen per revolution of the steel wheel was recorded, and the abrasion wear resistance of the specimen was reported as a “wear number” having units of krevs/cm³. Materials having a higher wear number are more resistant to abrasive wear than materials having a lower wear number as it requires a greater number of wheel revolutions on the testing equipment to abrade a unit volume of material.

The wear resistance number determined for each of Alloys A-F using the method of ASTM B611 is plotted in the graph in FIG. 12. Test results clearly show that the wear number, and thus the abrasion wear resistance, increased significantly with increasing cubic carbide content. As noted, the cobalt content of each of the alloys was adjusted so that each included approximately the same volume content of binder (cobalt). Nevertheless, Alloy B, including a total of 5 weight percent cubic carbides, was measured to have a wear number of about 5.75, while Alloy A, which lacked cubic carbides, was measured to have a wear number of only 5.1. Alloys C and D, which each had a cubic carbide content of 10 weight percent, were measured to have wear numbers in excess of 6, substantially greater than the wear numbers determined for Alloy A (lacking cubic carbides) and Alloy B (including half the weight percentage of cubic carbide). Alloys E and F, which included cubic carbide only in the form of tantalum carbide, also were measured to have a wear number (5.3) that is significantly greater than the wear number of Alloy A.

The fracture toughness of each of Alloys A-F was measured using the method described in ASTM B771-11e1 (“Standard Test Method for Short Rod Fracture Toughness of Cemented Carbides”). The fracture resistance property determined by this test method is believed to characterize the resistance of a cemented carbide to fracture in a neutral environment in the presence of a sharp crack under severe tensile constraint, such that the state of stress near the crack front approaches tri-tensile plane strain, and the crack-tip plastic region is small compared with the crack size and specimen dimensions in the constraint direction. The results of the testing are presented in Table 2 below.

TABLE 2

Material
Fracture Toughness (ksi · √in)

Alloy A
13.6

Alloy B
12.3

Alloy C
11.7

Alloy D
10.5

Alloy E
12.6

Alloy F
12.5

The results in Table 2 show that the significant improvements in wear resistance provided by the addition of cubic carbides are accompanied by the loss of some fracture toughness. However, the improvements in wear resistance achieved by the materials including cubic carbides are believed to outweigh the loss in fracture toughness in many applications of cemented carbides including, for example, most rock drilling applications in the oil, gas, and mining fields.

It will be understood that the present description illustrates those aspects of the invention relevant to a clear understanding of the invention. Certain aspects that would be apparent to those of ordinary skill in the art and that, therefore, would not facilitate a better understanding of the invention have not been presented in order to simplify the present description. Although only a limited number of embodiments of the present invention are necessarily described herein, one of ordinary skill in the art will, upon considering the foregoing description, recognize that many modifications and variations of the invention may be employed. All such variations and modifications of the invention are intended to be covered by the foregoing description and the following claims.

CUTTING INSERTS FOR EARTH-BORING BITS

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