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JP-2026514487-A - Heat treatment of cast tungsten carbide particles to improve impact resistance

JP2026514487AJP 2026514487 AJP2026514487 AJP 2026514487AJP-2026514487-A

Abstract

Cast tungsten carbide powder, a method for producing the powder, and raw materials containing the powder include a powder containing a tungsten carbide (monocarbide) phase and a metallic tungsten phase. Cast tungsten carbide powder may contain residual amounts of W₂C (hemicarbide) phase. [Selection Diagram] Figure 1

Inventors

  • ラルーシュ，ベルナール
  • ジャン，ジェ
  • ワン，ジョンミン
  • ベル，アンドリュー

Assignees

  • エリコン メテコ（ユーエス）インコーポレイテッド

Dates

Publication Date
20260511
Application Date
20240426
Priority Date
20230427

Claims (20)

  1. Cast tungsten carbide powder, Cast tungsten carbide powder comprising a tungsten carbide (monocarbide) phase, a metallic tungsten phase, and a residual amount of hemicarbide ( W₂C ) phase.
  2. The cast tungsten carbide powder according to claim 1, wherein the carbon content is 3.0 to 4.5% by weight.
  3. The cast tungsten carbide powder according to claim 1, wherein the shape of the cast tungsten carbide powder is at least one of the following: substantially angular, having a ratio of a first length along the major axis to a second length along the minor axis greater than 1.2; or substantially spherical, having a ratio of a first length along the major axis to a second length along the minor axis of 1.2 or less.
  4. The cast tungsten carbide powder according to claim 1, wherein the powder contains 1% to 50% tungsten phase.
  5. The cast tungsten carbide powder according to claim 1, wherein the powder has a thermal conductivity that is 1.1 to 3.5 times, preferably 1.1 to 3.0 times, and most preferably 1.1 to 2.5 times higher than a standard CTC carbide consisting of a monocarbide (WC) phase and a hemicarbide (W₂C) phase that have not been heat-treated.
  6. The cast tungsten carbide powder according to claim 1, wherein the powder has 1.1 to 8.0 times, preferably 1.2 to 7.0 times, and most preferably 1.6 to 6.5 times higher thermal shock resistance than a standard CTC carbide consisting of a monocarbide ( WC ) phase and a hemicarbide (W₂C) phase that has not undergone heat treatment.
  7. It is a raw material, A raw material comprising the cast tungsten carbide powder described in claim 1 and a metal alloy.
  8. The raw material according to claim 7, further comprising standard cast tungsten carbide powder having a WC phase and a W2C phase.
  9. The raw material according to claim 8, wherein the fraction of carbides from the cast tungsten carbide powder is 10 to 100% by weight of the total carbide fraction, preferably 20 to 90% by weight of the total carbide fraction, and most preferably 30 to 80% by weight of the total carbide fraction.
  10. The raw material according to claim 7, wherein the cast tungsten carbide powder has one unimodal size distribution among 45-325 mesh, 45-60 mesh, 60-100 mesh, 70-200 mesh, 100-200 mesh, 100-325 mesh, 200-325 mesh, or 200-450 mesh.
  11. The raw material according to claim 7, wherein the cast tungsten carbide powder has a bimodal size distribution in non-overlapping ranges, comprising one of the following: carbide particles of 45-60 mesh and 200-325 mesh; carbide particles of 45-60 mesh and 200-450 mesh; carbide particles of 45-60 mesh and 100-325 mesh; carbide particles of 45-60 mesh and 100-200 mesh; carbide particles of 40-80 mesh and 100-325 mesh; carbide particles of 60-100 mesh and particles of 100-325 mesh.
  12. The raw material according to claim 7, wherein the shape of the cast tungsten carbide powder is at least one of the following: substantially angular, having a ratio of a first length along the major axis to a second length along the minor axis greater than 1.2; or substantially spherical, having a ratio of a first length along the major axis to a second length along the minor axis of 1.2 or less.
  13. The raw material according to claim 11, wherein the carbide particles within the upper range of the bimodal size distribution constitute 30 to 80% by weight of the total carbide components of the raw material.
  14. The raw material according to claim 7, wherein the metal alloy includes nickel, cobalt, copper, or an iron alloy.
  15. The raw material according to claim 7, having a total weight fraction containing 5 to 95% by weight of carbides, preferably 50 to 90% by weight of carbides, and most preferably 60 to 80% by weight of carbides.
  16. A method for forming cast tungsten carbide powder, A mixture of tungsten and carbon is poured into a mold and rapidly cooled to form a material containing a cubic WC1 -X phase, a W2C (semicarbide) phase, and a WC (monocarbide) phase. A method comprising: sieving the particles of the material into a powder within a predetermined particle size range; and heat-treating the powder to at least partially convert the W2C (semicarbide) phase into a WC (monocarbide) phase and a W (metallic tungsten) phase in the heat-treated powder.
  17. The method according to claim 16, wherein the cast tungsten carbide powder comprises a tungsten carbide (monocarbide) phase, a metallic tungsten phase, and a residual amount of hemicarbide ( W₂C ) phase.
  18. Before sieving the particles of the material, the above method is performed The method according to claim 16, further comprising at least one of the following: spraying the formed material onto spherical particles while it is in a molten state, or spraying the formed material onto spherical particles while it is in a molten state, cooling the spherical particles, and crushing the cooled spherical particles into angular particles.
  19. The method according to claim 18, wherein the angular particles undergo further spheroidization.
  20. The method according to claim 16, wherein the tungsten phase in the heat-treated powder is in the range of 1% to 50% by weight.

Description

(Cross-reference of related applications) This application is an international application claiming priority to U.S. Provisional Application No. 63/462,407, filed on 27 April 2023, the disclosures of which are incorporated herein by reference in their entirety. (Field of invention) The embodiments concern the effects of heat treatment on cast tungsten carbide (CTC) powder on the mechanical and tribological properties of the material. Commercially available cast tungsten carbide (CTC) powder is generally produced by molten casting a mixture of tungsten and carbon in a graphite crucible. The molten material is cast and rapidly quenched in a water-cooled copper mold to form a very hard carbide with a fine microstructure. This material is then ground into finer particles with a horn-like shape and sieved to obtain the desired particle size range. These horn-like CTC particles can also be melted in a high-temperature plasma or graphite furnace to produce spherical particles of the same material. The carbon content is generally 3.7–4.1 wt% C (37.0–39.6 atomic%), which roughly corresponds to the carbon content of the cubic WC1-X phase formed at the start of liquid solidification at approximately 2735°C (see W-C phase diagram (Figure 1)). This cubic phase rapidly decomposes into hemicarbide W₂C and monocarbide WC via eutectoid reaction (2530°C), thus generating a very fine, feathery microstructure of both phases. According to the W-C phase diagram in Figure 1, the W₂C phase is stable only at temperatures above 1250°C and should be converted to WC and metallic tungsten via eutectoid reaction. However, due to the rapid cooling rate of the manufacturing process, the W₂C phase formed at high temperatures is retained after cooling to room temperature. Therefore, the typical final eutectoid microstructure of CTC after cooling consists of fine, alternating plates of metastable W₂C and WC (stable at room temperature). The proportion of each phase in the powder is approximately 75% W₂C and 25% WC. CTC powder is used with a metal binder (matrix) to create surface hardening on steel parts using welding/cladding or brazing processes. The powder is primarily used in applications requiring good wear resistance and impact resistance, such as drill bits and stabilizers for the petroleum industry, ground engagement tools, crushing hammers and rollers in mining, rock cutting and tunnel boring, and other applications subjected to heavy abrasion. One of the drawbacks of CTC powder is its extremely high hardness (>2300 HV), which results in a brittle material. In fact, the main phase of the carbide, W₂C , is known to be harder than the WC phase but more brittle. This property reduces the fracture toughness of the carbide powder and degrades the performance of CTC powder in applications subject to impact abrasion. The embodiment relates to CTC powder in which the brittle W2C phase is converted to the WC phase and more ductile metallic tungsten by heat treatment. In this way, CTC powder with better toughness can be obtained, and therefore, coatings (surface hardening) containing these carbides with improved wear resistance and impact resistance can be achieved. According to the embodiment, heat treatment of CTC powder can have many beneficial effects on the mechanical and tribological properties of the material. Firstly, the microstructure of the carbide is improved by converting W₂C (phase hemicarbide) into very fine WC (monocarbide) and metallic tungsten phases. In particular, a very fine eutectoid microstructure (small crystal size) consisting of alternating WC and W plates is thus produced by the eutectoid reaction of the metastable hemicarbide phase at temperatures below 1250°C. Another beneficial effect of heat treatment of CTC powder is the removal of free carbon (black smoke) often present in standard CTC. This is because black smoke is a soft and brittle compound that impairs the properties of the carbide in terms of hardness, toughness, and wear resistance. The embodiment relates to cast tungsten carbide powder containing a tungsten carbide (monocarbide) phase and a metallic tungsten phase. It may also contain a residual amount of hemicarbide ( W₂C ) phase. In embodiments, the shape of the CTC powder may be substantially angular or substantially spherical. Substantially angular carbides may have a ratio of a first length along the major axis to a second length along the minor axis that is greater than 1.2. Substantially spherical carbides have a ratio of a first length along the major axis to a second length along the minor axis that is 1.2 or less. In this embodiment, the cast tungsten carbide powder has a carbon content of 3.0 to 4.5% by weight. In one embodiment, the CTC powder contains metallic tungsten phase in a fraction of 1% to 50% by weight, preferably 5% to 50% by weight, and most preferably 10% to 50% by weight. In the embodiment, the CTC powder, without heat treatment, has a thermal conductivity 1.1 to 3.5 times hig