Sintered cemented carbide article and method for producing a sintered cemented carbide article

Abstract

Sintered hard metal article consisting of: Tungsten carbide as a hard particle phase and 1 to 30 wt.% of a metallic binder phase consisting of cobalt and a ruthenium alloy additive, wherein the ruthenium alloy additive is present in an amount of up to 50 wt.% of the metallic binder phase; wherein the carbon content of the sintered cemented carbide article is 94% to 98% of the stoichiometric carbon content of the sintered cemented carbide article, wherein the stoichiometric carbon content is the theoretical carbon content of 6.13 wt% of WC; wherein the sintered cemented carbide article has a magnetic saturation (MS) in the range of 49% to 73% and no eta phase; wherein the sintered cemented carbide article has a hardness of 80-94 HRA; wherein the cemented carbide article comprises a coating of one or more layers of refractory material deposited by chemical vapor deposition (CVD), physical vapor deposition (PVD), or combinations thereof; wherein one or more layers of the refractory coating have been subjected to a post-coating treatment such as polishing and / or blasting; and wherein the sintered cemented carbide article is a cutting tool, a tool for earth drilling applications, or a cemented carbide article for casting applications.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to sintered cemented carbide articles, and more particularly to sintered cemented carbide articles with low magnetic saturation and no eta phase. Furthermore, the present invention relates to methods for producing such sintered cemented carbide articles. BACKGROUND

[0002] Sintered cemented carbide articles, both coated and uncoated, have been used for various tool applications, such as cutting tools and wear parts. Increasing the resistance of sintered cemented carbide to wear and other failure modes, including thermal fatigue, fracture, and chipping, remains an area of ​​intense research and development. To this end, significant resources have been devoted to the development of wear-resistant refractory coatings for cutting tools. For example, TiC, TiCN, TiOCN, TiN, and Al2O3 have been applied to cemented carbides by chemical vapor deposition (CVD) and physical vapor deposition (PVD).

[0003] In addition, the properties of the underlying cemented carbide substrates were investigated. Cutting tool manufacturers have investigated changes in the composition of cemented carbide bodies and the resulting effects on cemented carbides' properties, including but not limited to hardness, wear resistance, thermal deformation resistance, toughness, and density. However, an improvement in one cemented carbide property often results in a concomitant deterioration of another. For example, increased deformation resistance of the cemented carbide can result in reduced toughness and thermal conductivity.Nevertheless, improvements in cemented carbide bodies are needed to meet the evolving demands of metalworking applications, and a balance between competing properties is required when making changes in the composition of cemented carbide bodies in efforts to provide cutting tools with improved performance.

[0004] DE 01 007 751 T1 discloses a cermet comprising at least one hard material and a cobalt-nickel-iron binder. The hard material comprises at least one carbide, for example, tungsten carbide.

[0005] US 2005 / 0 072 269 A1 shows segmented carbide blanks from which complex-shaped bodies can be obtained by spark erosion. The carbide blanks contain tungsten carbide as the hard material, with chromium, cobalt, nickel, and molybdenum as binders.

[0006] US 2011 / 0 286 877 A1 discloses a process for producing a sintered hard metal based on tungsten carbide. A binder is used that must contain 0.1 to 10 percent molybdenum by weight.

[0007] US 2012 / 0 210 822 A1 shows hard metals comprising tungsten carbide grains in a size in the nanometer range and a binder made of cobalt or cobalt and nickel.

[0008] US 2013 / 0 105 231 A1 discloses various cutting inserts made of a cemented carbide. The cemented carbide comprises a carbide phase and a metallic binder.

[0009] The article by Roebuck, B.: “Magnetic moment (saturation) measurements on hardmetals” (International Journal of Refractory Metals & Hard Materials, Vol. 14, 1996, No. 5-6, pp. 419-424, ISSN 0263-4368) describes relationships between the chemical composition of hard metals and their magnetic saturation.

[0010] WO 2014 / 122306 A2 discloses tungsten carbide-based hard metal materials containing 3 to 10 weight percent cobalt and 0.5 to 8 weight percent rhenium. The carbon content of the hard metal materials ranges from 6.3 to 6.9 weight percent. SUMMARY

[0011] The object of the invention is achieved by a sintered hard metal article according to claim 1 and a method for producing a sintered hard metal article according to claim 8.

[0012] In one aspect, sintered cemented carbide articles are described herein which, in some embodiments, exhibit improved resistance to wear and thermal fatigue. Furthermore, sintered cemented carbide articles described herein can tolerate variations in carbon content without the formation of undesirable phases, including eta phase and / or free graphite (C-type porosity). Such tolerance can facilitate the manufacture and use of cemented carbide grades in which carbon content is not strictly controlled.A sintered cemented carbide article described herein comprises tungsten carbide as the hard particle phase and a metallic binder phase comprising cobalt and a ruthenium alloy additive, wherein the sintered cemented carbide article has a magnetic saturation (MS) in the range of 49% to 73% and no eta phase, and wherein the carbon content of the sintered cemented carbide article is 94% to 98% of the stoichiometric carbon content of the sintered cemented carbide article, the stoichiometric carbon content being the theoretical carbon content of 6.13 wt% of WC. MS values ​​reported herein are based on the magnetic component(s) of the metallic binder phase.

[0013] From another aspect, methods for producing sintered cemented carbide articles as previously presented are described herein. The method described herein comprises providing a low-carbon powder grade including a tungsten carbide phase and a metallic binder phase comprising cobalt. A ruthenium alloy additive is provided for the metallic binder phase of the powder grade, and the powder grade is consolidated into a green compact. The green compact is sintered at a temperature of 1350-1560°C to provide a sintered cemented carbide article having an MS of 49% to 73% and no eta phase. The carbon content of the powder grade ranges from 94% to 98% of the stoichiometric carbon content of the powder grade.

[0014] These and other embodiments are described in more detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 illustrates the variation of MS with the carbon content of the sintered cemented carbide using metallic binder with alloying additives according to some embodiments described herein. DETAILED DESCRIPTION

[0015] Embodiments described herein will be more readily understood from the following detailed description and examples, and from their preceding and following descriptions. However, elements, devices, and methods described herein are not limited to the specific embodiments presented in the detailed description and examples. It should be understood that these embodiments merely illustrate the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those skilled in the art without departing from the scope of the claims.

[0016] In one aspect, sintered cemented carbide articles are described herein, which, in some embodiments, exhibit improved resistance to wear and thermal fatigue. A sintered cemented carbide article described herein comprises tungsten carbide as the hard particle phase and a metallic binder phase consisting of cobalt and a ruthenium alloy additive, wherein the sintered cemented carbide article has an MS in the range of 49% to 73% and no eta phase.

[0017] With respect to specific components, the hard particle phase may be present in the sintered cemented carbide article in any amount that does not conflict with the objectives of the present invention. The hard particle phase is present in an amount of at least 70 weight percent or at least 80 weight percent of the sintered cemented carbide article. The hard particle phase may also be present in an amount selected from Table I. Table I - Hard particle phase content Wt.% Sintered cemented carbide article 70-98 80-98 85-96 88-95 89-98 90-97

[0018] As described herein, the hard particle phase includes tungsten carbide. According to the invention, tungsten carbide is the hard particle phase.

[0019] Furthermore, the hard particle phase can generally have an average grain size of less than 30 µm. For example, the hard particle phase can have an average grain size of less than 10 µm or 5 µm, such as 0.5-3 µm.

[0020] As described herein, the sintered cemented carbide article includes a metallic binder phase comprising a ruthenium alloying additive and the balance cobalt. Generally, the metallic binder phase is present in amounts of 1-30 wt.% of the sintered cemented carbide article. In some embodiments, the metallic binder phase is present in an amount selected from Table II. Table II - Wt.% metallic binder of the sintered cemented carbide 1-30 2-20 2-12 3-10 4-15 10-30

[0021] The alloying additive of the metallic binder phase comprises ruthenium. In some embodiments, the metallic alloying additive has a hexagonal closest packing (HCP) crystal structure. In other embodiments, the metallic alloying additive has a cubic crystal structure, such as face-centered cubic (FCC) or body-centered cubic (BCC).

[0022] The alloying additive may be present in the metallic binder phase in any useful amount to provide the sintered cemented carbide article with the low magnetic saturation values ​​described herein without forming an eta phase. Generally, the alloying additive is present in an amount of up to 50 wt.% of the metallic binder phase. For example, in some embodiments, the alloying additive is present in an amount of 10-30 wt.% or 30-50 wt.% of the metallic binder phase.

[0023] In some embodiments, a sintered cemented carbide article described herein further comprises a surface zone of alloy binder enrichment having a maximum alloy binder content greater than the alloy binder content in the bulk of the sintered article. The zone of binder enrichment may extend inwardly from the surface of the sintered article. In some embodiments, the alloy binder of the enrichment zone is stratified, having distinguishable layers of alloy binder. In other embodiments, the alloy binder is not stratified. The sintered cemented carbide article may have a surface zone of alloy binder enrichment on one or more surfaces.

[0024] The sintered cemented carbide article having the composition described herein has an MS of 49% to 73%. Notably, at these low MS values, the sintered cemented carbide article does not exhibit any eta phase, (CoW)C-type phases. In some embodiments, the sintered cemented carbide article having the composition described herein has an MS selected from Table III, in each case in combination with the aforementioned magnetic saturation MS range of 49% to 73%. Table III - MS of sintered cemented carbide article 0-73 0-70 3-73 5-70 15-60 20-65 30-65 40-65

[0025] Magnetic saturation values ​​reported herein are based on magnetic bonds of the metallic binder phase and are determined according to ASTM B 886-12, "Standard Test Method for Determination of Magnetic Saturation (MS) of Cemented Carbides," ASTM International. As is known to those skilled in the art, magnetic saturation values ​​can range from percent to µTm. 3 / kg or other comparable units based on a nominally pure Co binder phase. For example, see Roebuck, B. Magnetic Moment (Saturation) Measurements on Hardmetals, Int. J. Refractory Metals & Hard Materials, 14 (1996) 419-424. Additionally, sintered cemented carbide articles described herein have a hardness of 80-94 HRA.

[0026] Sintered cemented carbide articles of the composition described herein, and having the aforementioned MS and no eta phase, are low in carbon according to the invention. The carbon content of the sintered cemented carbide article is 94% to 98% of the stoichiometric carbon content of the sintered article. As described in detail in the examples below, the stoichiometric carbon content depends on certain compositional parameters of the sintered cemented carbide article and may therefore differ between sintered cemented carbide articles formed from different powder types. In some embodiments, the carbon content of the sintered cemented carbide article is selected relative to the stoichiometric carbon content from Table IV. Table IV - Carbon content of sintered cemented carbide article % of the stoichiometric carbon content for sintered cemented carbide article 85-99,5* 90-99,5* 82-99* 85-99* 90-99* 94-99* 82-98* 85-98* 90-98* 94-98 *: not in accordance with the claim

[0027] Such tolerance to variations in carbon content without the formation of eta phase and / or other lower carbides such as W2C can simplify the production and use of carbide grades and sintering conditions when carbon content is not strictly controlled. According to the invention, a carbon-deficient sintered cemented carbide body exhibits a MS of 49% to 734% and no eta phase.

[0028] Methods for producing sintered cemented carbide articles are described herein using carbon-deficient powder grades. The method described herein comprises providing a low-carbon powder grade including a tungsten carbide phase and a metallic binder phase comprising at least cobalt. A ruthenium alloy additive is provided for the metallic binder phase of the low-carbon powder grade, and the low-carbon powder grade is consolidated into a green compact. The green compact is sintered to provide a sintered cemented carbide article having an MS of 49% to 73% and no eta phase. In some embodiments, the sintered cemented carbide article has an MS value selected from Table III above.

[0029] The carbon content of the powder grade ranges from 94% to 98% of the stoichiometric carbon content of the powder grade. In some embodiments, the carbon content of the powder grade relative to the stoichiometric carbon content conforms to the values ​​provided in Table IV above. Sintered cemented carbide articles produced according to the present process may have any composition and / or properties listed hereinabove, including the carbon deficiencies provided in Table IV.

[0030] The alloying powder can be provided for the powder grade and ground or otherwise intimately mixed with the powder grade so that the tungsten carbide particles are in contact with the metallic binder powder, including the alloying additive. Alternatively, the metallic binder phase of the powder grade is pre-alloyed with the alloying additive. For example, metallic binder powder of the grade composition can be an alloy formed from cobalt and the alloying additive.

[0031] The green compact of the consolidated powder grade can be sintered under any conditions that do not conflict with the objectives of the present invention to provide a cemented carbide article described herein. For example, the green compact or blank can be vacuum sintered or hot isostatic press (HIP) sintered at a temperature in the range of 1350°C to 1560°C for a time sufficient to produce the desired density and microstructure.

[0032] According to the invention, sintered cemented carbide articles having compositions and properties described herein are coated with one or more refractory materials by PVD and / or CVD. In some embodiments, the refractory coating comprises one or more metallic elements selected from aluminum and metallic elements of Groups IVB, VB, and VIB of the Periodic Table, and one or more non-metallic elements of Groups IIIA, IVA, VA, and VIA of the Periodic Table. For example, the refractory coating may comprise one or more carbides, nitrides, carbonitrides, oxides, or borides of one or more metallic elements selected from aluminum and Groups IVB, VB, and VIB of the Periodic Table. Additionally, the coating may be single-layer or multi-layer.

[0033] Furthermore, surfaces of sintered cemented carbide articles described herein have been subjected to one or more treatments such as polishing, blasting, and / or etching. A refractory coating described herein can be applied to the treated surfaces of the sintered cemented carbide articles. Furthermore, according to the invention, one or more layers of the refractory coating are subjected to a post-coating treatment such as polishing and / or blasting.

[0034] Sintered cemented carbide articles having compositions and properties described herein can exhibit improved resistance to wear and thermal fatigue without a significant reduction in hardness. The sintered cemented carbide articles are therefore suitable for a number of tool applications. In some embodiments, sintered cemented carbide articles described herein are cutting tools. For example, sintered cemented carbide articles can be end mills, drills, or cutting inserts, including indexable cutting inserts. Sintered cemented carbide articles described herein can also be a tool for earth drilling applications, such as bit bodies, fixed cutting blades, and / or rotary cutting blades. Furthermore, the sintered cemented carbide articles can be used in casting applications as molds, punches, or extruder parts.

[0035] These and other embodiments are further illustrated by the following non-limiting examples. Example 1 - Sintered hard metal objects

[0036] Sintered cemented carbide articles with the compositions shown in Table V were prepared as follows. A powder grade containing 89 wt.% tungsten carbide particles with an average grain size of less than 5 µm, 9.5 wt.% cobalt binder powder, and 1.5 wt.% ruthenium alloying powder were vacuum sintered at a peak temperature of 1395 °C to provide the fully dense cemented carbide compositions. Tungsten metal powder (WMP) was added to the powder grade compositions in the percentages shown in Table V to make the powder grade low in carbon. In addition, carbon was added to the powder grade of Sample 6 to determine the formation of C porosity. The actual carbon content of each sintered cemented carbide article was compared to the stoichiometric carbon content for the as-sintered article.Since samples 1-6 employed WC as the sole carbide phase, the stoichiometric carbon content was determined using the theoretical carbon content of 6.13 wt% for WC. Examination of the eta phase was performed by grinding each sintered cemented carbide article as required and subsequently polishing it using a 1-micron Petrodisc polishing wheel. The quality of the polished surface was checked with an optical microscope at a magnification of 200x-500x. Repolishing was applied if necessary. The polished surface was etched using Murakami's etching solution for a minimum of three seconds. The etched surface was checked for eta phase using an optical microscope at a magnification of 150x. Table V - Sintered hard metal articles WC-9.5% Co-1.5% RuSample WMP added wt% AddedCarbonWt% Measured MS % Eta-phase C porosity HRA Measured carbon content wt% Total W content wt% Stoich. Carbon contentWt.% % Stoich. Carbon content 1 3,42 0 41,97 Eta 90,1 5,244 92,42 5,665 92,56 2 2,92 0 42,24 Eta 90,1 5,263 91,92 5,634 93,40 3 2,43 0 49,56 without 89,8 5,279 91,43 5,605 94,19 4 0,92 0 72,57 without 89,7 5,398 89,92 5,512 97,93 5 0 0 80,94 without 89,7 5,459 89,00 5,456 100,06 6 0 0,07 82,47 C-porosity 89,8 5,508 89,00 5,456 100,96

[0037] The results shown in Table V are in Fig.1 graphically illustrates this. The ruthenium alloy addition resulted in low MS values ​​and significantly improved the range in which no eta phase was formed. Additionally, the presence of the ruthenium alloy addition allowed the use of tungsten carbide with significant carbon deficiency without the formation of eta phase. Therefore, tungsten carbide feedstock with broader carbon distributions can be successfully used in the production of cemented carbide articles without the presence of eta phase and / or C porosity. Notably, as listed in Table V, the amount of ruthenium alloy addition remained constant across Samples 1-6. In some embodiments, additional alloy additions can be added to Samples 1-2, resulting in the elimination of the eta phase and further reducing the MS value described herein.

[0038] Various embodiments of the invention have been described which meet the various objectives of the invention. It should be understood that these embodiments merely illustrate the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those skilled in the art without departing from the scope of the claims.

Claims

[1] Sintered hard metal article consisting of: Tungsten carbide as a hard particle phase and 1 to 30 wt.% of a metallic binder phase consisting of cobalt and a ruthenium alloy additive, wherein the ruthenium alloy additive is present in an amount of up to 50 wt.% of the metallic binder phase; wherein the carbon content of the sintered cemented carbide article is 94% to 98% of the stoichiometric carbon content of the sintered cemented carbide article, wherein the stoichiometric carbon content is the theoretical carbon content of 6.13 wt% of WC; wherein the sintered cemented carbide article has a magnetic saturation (MS) in the range of 49% to 73% and no eta phase; wherein the sintered cemented carbide article has a hardness of 80-94 HRA; wherein the cemented carbide article comprises a coating of one or more layers of refractory material deposited by chemical vapor deposition (CVD), physical vapor deposition (PVD), or combinations thereof; wherein one or more layers of the refractory coating have been subjected to a post-coating treatment such as polishing and / or blasting; and wherein the sintered cemented carbide article is a cutting tool, a tool for earth drilling applications, or a cemented carbide article for casting applications. [2] The sintered cemented carbide article according to claim 1, wherein the MS is in the range of 49% to 65%. [3] The sintered cemented carbide article of claim 1, further comprising a metallic binder enriched zone at a surface of the article. [4] The sintered cemented carbide article according to claim 1, wherein the article is a cutting tool. [5] A sintered cemented carbide article according to claim 4, wherein the cutting tool is an indexable cutting insert. [6] A sintered cemented carbide article according to claim 4, wherein the cutting tool is an end mill or a drill. [7] A sintered cemented carbide article according to claim 1, wherein the article is a tool for earth drilling applications. [8] A method for producing a sintered hard metal article according to claim 1, comprising: Providing a low-carbon powder grade comprising a tungsten carbide phase and a metallic binder phase comprising cobalt, wherein the low-carbon powder grade has a carbon content of 94% to 98% of the stoichiometric carbon content of the powder grade, wherein the stoichiometric carbon content is the theoretical carbon content of 6.13 wt% WC; Providing a ruthenium alloy additive for the metallic binder phase of the powder grade; Solidifying the powder with the alloy additive to a green body at a temperature of 1350 - 1560 °C; and Sintering the green compact to provide the sintered cemented carbide article having an MS of 49% to 73% and no eta phase.

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