Cemented carbide
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Cemented carbides are a class of hard materials used extensively for cutting tools, as well as in other industrial applications. It consists of fine particles of carbide cemented into a composite by a binder metal. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites.
Most of the time, carbide cutters will leave a better surface finish on a part and allow for faster machining than high-speed steel or other tool steels. Carbide tools can withstand higher temperatures at the cutter-workpiece interface than standard high-speed steel tools (which is a principal reason enabling the faster machining). Carbide is usually superior for the cutting of tough materials such as carbon steel or stainless steel, as well as in situations where other cutting tools would wear away faster, such as high-quantity production runs. In situations where carbide tooling is not required, high-speed steel is preferred for its lower cost.
Construction
Cemented carbides are metal matrix composites where carbide particles act as the aggregate and a metallic binder serves as the matrix (analogous to concrete, where a gravel aggregate is suspended in a cement matrix). The structure of cemented carbide is conceptually similar to that of a grinding wheel, but the abrasive particles are much smaller; macroscopically, the material of a carbide cutter appears homogeneous.
The process of combining the carbide particles with the binder is referred to as sintering or hot isostatic pressing (HIP). During this process, the material is heated until the binder enters a liquid phase while the carbide grains (which have a much higher melting point) remain solid. At this elevated temperature and pressure, the carbide grains rearrange themselves and compact together, forming a porous matrix. The ductility of the metal binder serves to offset the brittleness of the carbide ceramic, resulting in the composite's high overall toughness and durability. By controlling various parameters, including grain size, cobalt content, dotation (e.g., alloy carbides) and carbon content, a carbide manufacturer can tailor the carbide's performance to specific applications.
The first cemented carbide developed was tungsten carbide (introduced in 1927) which uses tungsten carbide particles held together by a cobalt metal binder. Since then, other cemented carbides have been developed, such as titanium carbide, which is better suited for cutting steel, and tantalum carbide, which is tougher than tungsten carbide.[1]
Physical properties
The
Applications
Inserts for metal cutting
Carbide is
Insert coatings
To increase the life of carbide tools, they are sometimes coated. Five such coatings are TiN (
Inserts for mining tools
Mining and tunneling cutting tools are most often fitted with cemented carbide tips, the so-called "button bits". Artificial diamond can replace the cemented carbide buttons only when conditions are ideal, but as rock drilling is a tough job cemented carbide button bits remain the most used type throughout the world.
Rolls for hot-roll and cold-roll applications
Since the mid-1960s, steel mills around the world have applied cemented carbide to the rolls of their rolling mills for both hot and cold rolling of tubes, bars, and flats.
Other industrial applications
This category contains a countless number of applications, but can be split into three main areas:
- Engineered components
- Wear parts
- Tools and tool blanks
Some key areas where cemented carbide components are used:
- Automotive components
- Canning tools for cans
- Rotary cutters for high-speed cutting of artificial fibres
- Metal forming tools for drawing dies.
- Rings and bushings typically for bump and seal applications
- Woodworking, e.g., for sawing and planing applications
- Pump pistons for high-performance pumps (e.g., in nuclear installations)
- Nozzles, e.g., high-performance nozzles for oil drilling applications
- Roof and tail tools and components for high wear resistance
- Balls for ball bearings and ballpoint pens
Non-industrial uses
Jewellery
Tungsten carbide has become a popular material in the bridal jewellery industry, due to its extreme hardness and high resistance to scratching. Given its brittleness, it is prone to chip, crack, or shatter in jewellery applications. Once fractured, it cannot be repaired.
History
The initial development of cemented and
Although the marketing pitch was slightly hyperbolic (carbides being not entirely equal to diamond), carbide tooling offered an improvement in cutting speeds and feeds so remarkable that, like high-speed steel had done two decades earlier, it forced machine tool designers to rethink every aspect of existing designs, with an eye toward yet more rigidity and yet better spindle bearings.
During World War II there was a tungsten shortage in Germany. It was found that tungsten in carbide cuts metal more efficiently than tungsten in high-speed steel, so to economise on the use of tungsten, carbides were used for metal cutting as much as possible.
The
Uncoated tips brazed to their shanks were the first form. Clamped indexable inserts and today's wide variety of coatings are advances made in the decades since.[3] With every passing decade, the use of carbide has become less "special" and more ubiquitous.[original research?]
Regarding fine-grained hardmetal, an attempt has been made to follow the scientific and technological steps associated with its production; this task is not easy, though, because of the restrictions placed by commercial, and in some cases research, organisations, in not publicising relevant information until long after the date of the initial work. Thus, placing data in an historical, chronological order is somewhat difficult. However, it has been possible to establish that as far back as 1929, approximately 6 years after the first patent was granted, Krupp/Osram workers had identified the positive aspects of tungsten carbide grain refinement. By 1939, they had also discovered the beneficial effects of adding a small amount of
What was considered 'fine' in one decade was considered not so fine in the next. Thus, a grain size in the range 0.5–3.0 μm was considered fine in the early years, but by the 1990s, the era of the nano-crystalline material had arrived, with a grain size of 20–50 nm.
Pobedit
Pobedit (Russian: победи́т) is a
Pobedit is usually produced by powder metallurgy in the form of plates of different shapes and sizes. The manufacturing process is as follows: a fine powder of tungsten carbide (or other refractory carbide) and a fine powder of binder material such as cobalt or nickel both get intermixed and then pressed into the appropriate forms. Pressed plates are sintered at a temperature close to the melting point of the binder metal, which yields a very tight and solid substance.
The plates of this superhard composite are applied to manufacturing of metal-cutting and drilling tools; they are usually soldered on the cutting tool tips. Heat post-treatment is not required. The pobedit inserts at the tips of drill bits are still very widespread in Russia.
See also
References
- ISBN 978-0-340-69159-5.
- .
- ^ a b c d Machinery's Handbook (1996), p. 744.
- ^ a b ThyssenKrupp AG, 1926 Krupp markets WIDIA tool metal, Essen, Germany, archived from the original on 25 March 2016, retrieved 2 March 2012.
- ^ Burghardt & Axelrod (1954), p. 453.
- ^ Widia.com, retrieved 22 October 2010.
- .
- ^ "Победит [Pobedit]". Большая советская энциклопедия [Great Soviet Encyclopedia] (in Russian) (3 ed.). Советская энциклопедия [Soviet Encyclopedia]. 1975. Retrieved 21 June 2020.
- ^ Васильев, Н. Н.; Исаакян, О. Н.; Рогинский, Н. О.; Смолянский, Я. Б.; Сокович, В. А.; Хачатуров, Т. С. (1941). "ПОБЕДИТ [Pobedit]". Технический железнодорожный словарь [Technical Railway Dictionary] (in Russian). Трансжелдориздат [Transseldorizdat].
- ^ the free dictionary: pobedit
Bibliography
- Burghardt, Henry D.; Axelrod, Aaron (1954). Machine Tool Operation. Vol. 2 (3rd ed.). McGraw-Hill. LCCN 52011537.
- Oberg, Erik; Jones, Franklin D.; Horton, Holbrook L.; Ryffel, Henry H. (1996), Green, Robert E.; McCauley, Christopher J. (eds.), OCLC 473691581.
Further reading
- Schubert, W.-D.; Lassner, E.; Böhlke, W (June 2010). "Cemented Carbides – A Success Story" (PDF). ITIA Newsletter.
- "Cemented Carbides in the Soviet Union – The Unknown History". Tungsten (ITIA Newsletter).
External links
Media related to Cemented carbides at Wikimedia Commons