Hard alloys are hard and wear-resistant metallic materials capable of retaining these properties at 900–1150 ° C. They are mainly made of high-hard and refractory materials based on tungsten , titanium , tantalum, chromium carbides , bound with a cobalt metal bond, with different cobalt or nickel contents.
Content
Types of hard alloys
There are sintered and cast hard alloys. The main feature of sintered hard alloys is that products made from them are obtained by powder metallurgy methods and they can only be processed by grinding or physico-chemical processing methods (laser, ultrasound, etching in acids, etc.) are also perfectly processed by electro-physical method of erosion, cast hard alloys are designed for surfacing on the instrument to be equipped and undergo not only mechanical, but often also heat treatment (quenching, annealing, aging, etc.). Powder hard alloys are fixed on the instrument to be equipped with soldering methods or mechanical fastening.
Hard alloys are distinguished by carbide metals, in which they are present: tungsten - VK2, VK3, VK3M, VK4B, VK6M, VK6, VK6B, VK8, VK8V, VK10, VK15, VK20, VK25; titanium-tungsten - T30K4, T15K6, T14K8, T5K10, T5K12V; titanium-tantalum-tungsten - ТТ7К12, ТТ10К8Б. Tungsten-free TNM20, TNM25, TNM30
By chemical composition, hard alloys are classified:
- tungsten-cobalt hard alloys (VK);
- titan-tungsten-cobalt hard alloys (TC);
- titanotantale tungsten-cobalt hard alloys (TTC).
Hard alloys for the intended purpose are divided (ISO classification) into:
- Р - for steel castings and materials, during the processing of which drain chips are formed;
- M - for processing difficult-to-cut materials (usually stainless steel);
- K - for the treatment of cast iron;
- N - for processing aluminum, as well as other non-ferrous metals and their alloys;
- S - for the treatment of superalloys and alloys based on titanium;
- H - for hardened steel.
Due to a shortage of tungsten , a group of tungsten -free hard alloys, called cermets, has been developed. These alloys contain titanium carbides (TiC), titanium carbonitrides (TiCN), linked by a nickel-molybdenum base. The technology of their manufacture is similar to tungsten-containing hard alloys.
Compared with tungsten hard alloys, these alloys have lower flexural strength, impact strength, are sensitive to temperature differences due to low thermal conductivity , but have the advantages of increased heat resistance (1000 ° C) and low adhesion to the materials being processed, due to which they are not prone to growth during cutting. Therefore, they are recommended to be used for fine and semi- turning turning , milling . To destination belong to group P of classification of ISO.
Properties of hard alloys
Plates of hard alloy have HRA 86-92 have high wear resistance and redness (800–1000 ° C), which allows processing at cutting speeds of up to 800 m / min.
Sintered hard alloys
Hard alloys are made by sintering a mixture of powders of carbides and cobalt . The powders are prefabricated by chemical reduction (1-10 microns), mixed in an appropriate ratio and pressed under pressure of 200-300 kgf / cm², and then sintered in forms corresponding to the size of the finished plates, at a temperature of 1400-1500 ° C, in a protective atmosphere . Hard alloys are not subjected to heat treatment , since they immediately after manufacture have the required set of basic properties.
Composite materials consisting of a metal-like compound, cemented by metal or alloy . Their basis is most often tungsten or titanium carbides, complex tungsten and titanium carbides (often also tantalum ), titanium carbonitride, less often other carbides , borides, etc. As a matrix, the so-called " bundle "- metal or alloy. Usually cobalt is used as a “bond”, since cobalt is a neutral element with respect to carbon, it does not form carbides and does not destroy carbides of other elements, less often nickel , its alloy with molybdenum (nickel-molybdenum bond).
Production of hard alloys by powder metallurgy
- Production of carbide and cobalt powders by reduction from oxides.
- Grinding powders of carbides and cobalt (produced on ball mills within 2-3 days) to 1-2 microns.
- Screening and regrinding as necessary.
- Mix preparation (powders are mixed in quantities corresponding to the chemical composition of the alloy being produced).
- Cold pressing (organic glue is added to the mixture to temporarily preserve the shape, for example, PVA , paraffins or glycerin [1] ).
- Sintering under load (hot pressing) at 1,400 ° C (at 800–850 ° C, the glue burns without residue). At 1400 ° C, the cobalt melts and wets the carbide powders; upon subsequent cooling, the cobalt crystallizes, combining the carbide particles.
Nodes of sintered hard alloys
Hard alloys can be divided into three main groups:
- tungsten-containing hard alloys
- titanium-tungsten-containing hard alloys
- titanium tantalum tungsten hard alloys
Each of the above groups of hard alloys is subdivided in turn into grades that differ in chemical composition, physical-mechanical and operational properties.
Some alloy grades, having the same chemical composition, differ in the grain size of the carbide constituents, which determines the difference in their physical-mechanical and operational properties, and hence the fields of application.
The properties of grades of hard alloys are designed in such a way that the manufactured range can satisfy the needs of modern production to the maximum extent. When choosing the grade of the alloy should be considered: the scope of the alloy, the nature of the requirements for the accuracy of the surfaces to be treated, the state of the equipment and its kinematic and dynamic data.
Designations of grades of alloys are built according to the following principle:
Group 1 - alloys containing tungsten carbide and cobalt. Denoted by the letters VK, after which the numbers indicate the percentage in the alloy of cobalt. The following brands belong to this group:
VKZ, VKZM, VK6, VK6M, VK6OM, VK6KS, VK6B, VK8, VK8K, VK8V, VK10KS, VK15, VK20, VK20KS, VK10HOM, VK4B.
Group 2 - titanium-tungsten alloys, having in its composition titanium carbide, tungsten carbide and cobalt. It is denoted by the letters TK, while the figure after the letters T denotes the% content of titanium carbides, and after the letter K - the content of cobalt. The following brands belong to this group: T5K10, T14K8, T15K6, TZ0K4.
Group 3 - titanotantalum tungsten alloys, having in its composition titanium, tantalum and tungsten carbide, as well as cobalt are denoted by the letters TTK, while the figure after TT is the content of titanium and tantalum carbides, and after the letter K is the content of cobalt. The following brands belong to this group: TT7K12, TT20K9.
Group 4 - alloys with wear-resistant coatings. Have a letter ID VP. The following brands belong to this group: VP3115 (basis of VK6), VP3325 (basis of VK8), VP1255 (basis of ТТ7К12).
Hard alloys used for metal cutting: VK6, VKZM, VK6M, VK60M, VK8, VK10HOM, TZOK4, T15K6, T14K8, T5K10, TT7K12, TT20K9.
The hard alloys used for brushless treatment of metals and wood, wear parts of machines, devices and devices: VKZ, VKZM, VK6, VK6M, VK8, VK15, VK20, VK10KS. VK20KS.
Hard alloys used to equip mining tools: VK6V, VK4V, VK8VK, VK8, VK10KS, VK8V, VK11VK, VK15.
In Russia and the former USSR, the following sintered hard alloys are used for metal cutting [2] :
| Mark alloy | WC% | TiC% | TaC% | Co% | Flexural strength (σ) MPa | Hardness HRA | Density (ρ) g / cm3 | Thermal conductivity (λ), W / (m · ° C) | Young's modulus (E), GPa |
|---|---|---|---|---|---|---|---|---|---|
| VK2 | 98 | - | - | 2 | 1200 | 91.5 | 15.1 | 51 | 645 |
| VK3 | 97 | - | - | 3 | 1200 | 89.5 | 15.3 | 50.2 | 643 |
| VK3-M | 97 | - | - | 3 | 1550 | 91 | 15.3 | 50.2 | 638 |
| VK4 | 96 | - | - | four | 1500 | 89.5 | 14.9-15.2 | 50.3 | 637.5 |
| VK4-B | 96 | - | - | four | 1550 | 88 | 15.2 | 50.7 | 628 |
| VK6 | 94 | - | - | 6 | 1550 | 88.5 | 15 | 62,8 | 633 |
| VK6-M | 94 | - | - | 6 | 1450 | 90 | 15.1 | 67 | 632 |
| VK6-OM | 92 | - | 2 | 6 | 1300 | 90.5 | 15 | 69 | 632 |
| VK8 | 92 | - | - | eight | 1700 | 87.5 | 14.8 | 50.2 | 598 |
| VK8-B | 92 | - | - | eight | 1750 | 89 | 14.8 | 50.4 | 598.5 |
| BK10 | 90 | - | - | ten | 1800 | 87 | 14.6 | 67 | 574 |
| VK10-OM | 90 | - | - | ten | 1500 | 88.5 | 14.6 | 70 | 574 |
| BK15 | 85 | - | - | 15 | 1900 | 86 | 14.1 | 74 | 559 |
| BK20 | 80 | - | - | 20 | 2000 | 84.5 | 13.8 | 81 | 546 |
| BK25 | 75 | - | - | 25 | 2150 | 83 | 13.1 | 83 | 540 |
| VK30 | 70 | - | - | thirty | 2400 | 81.5 | 12.7 | 85 | 533 |
| T5K10 | 85 | 6 | - | 9 | 1450 | 88.5 | 13.1 | 20.9 | 549 |
| T5K12 | 83 | five | - | 12 | 1700 | 87 | 13.5 | 21 | 549.3 |
| T14K8 | 78 | 14 | - | eight | 1300 | 89.5 | 11.6 | 16.7 | 520 |
| T15K6 | 79 | 15 | - | 6 | 1200 | 90 | 11.5 | 12.6 | 522 |
| T30K4 | 66 | thirty | - | four | 1000 | 92 | 9.8 | 12.57 | 422 |
| TT7K12 | 81 | four | 3 | 12 | 1700 | 87 | 13.3 | ||
| TT8K6 | 84 | eight | 2 | 6 | 1350 | 90.5 | 13.3 | ||
| TT10K8-B | 82 | 3 | 7 | eight | 1650 | 89 | 13.8 | ||
| TT20K9 | 67 | 9.4 | 14.1 | 9.5 | 1500 | 91 | 12.5 | ||
| TN-20 | - | 79 | (Ni15%) | (Mo6%) | 1000 | 89.5 | 5.8 | ||
| TN-30 | - | 69 | (Ni23%) | (Mo29%) | 1100 | 88.5 | 6 | ||
| TN-50 | - | 61 | (Ni29%) | (Mo10%) | 1150 | 87 | 6.2 |
Foreign manufacturers of cemented carbides, as a rule, each use their own alloy grades and designations.
Developments
Currently [ when? ] in the Russian carbide industry, in-depth studies are being conducted related to the possibility of improving the performance properties of hard alloys and expanding the scope of application. First of all, these studies relate to the chemical and particle size distribution of RTP (ready-to-press) mixtures. One of the most successful examples of recent times can be alloys of the TSN group (TU 1966-1001-00196121-2006), developed specifically for working friction units in corrosive acidic environments. This group is a logical continuation of the chain of VN alloys on the nickel bond, developed by the All-Russian Research Institute of Hard Alloys . It was experimentally observed that with a decrease in the grain size of the carbide phase in a hard alloy, the hardness and strength are qualitatively increased. The technology of plasma restoration and regulation of the particle size distribution at the moment allows the production of hard alloys with grain sizes (WC) in which may be less than 1 micrometer. Alloys of TSN-group are widely used in the production of nodes of chemical and oil and gas pumps of Russian production.
Cast hard alloys
Cast hard alloys are obtained by melting and casting .
Application
Hard alloys are currently a common tool material widely used in the tool industry. Due to the presence of refractory carbides in the structure, carbide tools have high hardness HRA 80-92 (HRC 73-76), heat resistance (800–1000 ° C), so they can work with speeds several times higher than cutting speeds for high-speed steels. However, unlike high-speed steels, hard alloys have a lower strength (σ and = 1000–1500 MPa) and do not have toughness . Hard alloys are low-tech: because of their great hardness, it is impossible to make a solid shaped tool, besides they are limitedly polished - only with diamond tools, therefore hard alloys are used in the form of plates, which are either mechanically fixed on the tool holders or soldered to them.
Due to its high hardness, hard alloys are used in the following areas:
- Cutting construction materials: cutters , cutters , drills , broaches and other tools.
- Equipment of measuring instrument: equipment of exact surfaces of micrometric equipment and supports of scales.
- Branding: equipping the working part of the stamps.
- Drawing: equipping the working part of the fiber .
- Stamping: equipment of dies and dies (cutting, extrusion, etc.).
- Rolling: carbide rolls (made in the form of rings made of hard alloy, worn on a metal base)
- Mining equipment: soldered sintered and overlaying cast carbide.
- Production of wear-resistant bearings: balls, rollers, clips and spraying on steel.
- Ore-processing equipment: equipment of working surfaces.
- Thermal spraying of wear - resistant coatings
See also
- Sintered materials
- Chrome-Cobalt-Molybdenum Alloys
Notes
- ↑ 7. Forming ceramic blanks
- ↑ GOST 3882-74 Archive dated November 4, 2011 on the Wayback Machine ( PDF , 1.98 MB)
Links
Basic principles for the designation of grades of alloys. Hard alloys - Classification, applications
Literature
- Construction materials. Ed., B. N. Arzamasov. Moscow, Mashinostroenie, 1990.
- Technology of construction materials. Ed. A. M. Dalsky. Moscow, Mashinostroenie, 1985.
- Stepanchuk A.N., Bilyk I.I., Boyko P.A. Technology of powder metallurgy. - K .: Vishcha shk., 1989.-415с.
- Skorokhod V.V. Powder materials based on refractory metals and compounds. - K .: Tekhnika, 1982.-167с.