In today’s knife industry, powder steels are playing an increasingly important role. High wear resistance, toughness and durability – these are the qualities that consumers get from the use of a wide variety of powders. Vanadium, a gray-colored metal that forms strong carbides during heat treatment, plays the most important role in their composition.
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Vanadium is a chemical element designated by the symbol V and atomic number 23. It was discovered in 1801 by Spanish mineralogist A. Del Rio, and then rediscovered in 1830 by Swedish chemist N. Sefström. Metallic vanadium was first produced in 1867, and the first vanadium steel was smelted in England in 1903. And then throughout the 20th century the role of vanadium in metallurgy was constantly increasing.
Vanadium is a very common metal on our planet. It is primarily found in the Earth’s crust, where it is bound to various minerals. In addition to soil, it can be found in seawater, petroleum, humans and animals. Vanadium plays a role in the control of phosphorylation enzymes and is used by bacteria for nitrogen fixation. Vanadium ores, primarily titanium-magnetite ores, as well as carnotite and patronite, are the main source of its extraction. Pure vanadium has high strength, softness, and is not magnetic. It is similar to titanium in most qualities. Vanadium ore is most common in South America, China, and Russia.
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In production processes, vanadium is used in the form of an iron-vanadium alloy (ferrovanadium) with at least 50% of its content. To create the alloy, vanadium and iron-containing slag are reduced with ferrosilicon and lime. The production of this metal takes several steps. During the initial smelting in the blast furnace process, the vanadium remains in the pig iron and is then converted to slag containing up to 25% vanadium oxide. The next step is oxidative roasting with the addition of various acids and salts. Vanadium in the form of metal is obtained by reduction of vanadium oxide. In this process, aluminum or calcium are most often involved, as the use of other substances does not provide the necessary purity of the final product.
For the use of vanadium in powder steel production, its carbide (VC), a binary compound in the form of black crystals, is used. The main reason for its use as the main material in alloying is the formation of hard carbide, which can not only exist on its own, but can also be incorporated into chromium, tungsten and molybdenum carbides to increase their hardness. It can be introduced into the steel in large quantities, which does not adversely affect the uniformity of distribution of small carbides. Thus the amount of vanadium in the alloy can be very large. Its use also improves the heat treatment capabilities, allowing the thermologist to “squeeze” the most out of the steel.
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A large amount of vanadium in steel also has its disadvantages. First of all, it complicates its grindability and increased scale formation. These features of vanadium make “powders” difficult to process and sharpen, and the higher its content in the composition, the more difficult it is to achieve the result. Mechanical processing of high vanadium steel requires professionalism, extensive experience and the strictest possible adherence to technology.
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For “ordinary”, non-powder steels, the limit is up to 12%, for powder steels – up to 15% of the volume. To improve the properties of such alloys in the last twenty years, metallurgists have begun to use alloying with niobium and nitrogen, which somewhat facilitate further processing. It is also important to remember that an increase in wear resistance is always accompanied by deterioration of other qualities of specific alloys. For example, powder steels with vanadium content in the limits of 10% retain mechanical properties well, but already at 15% their strength drops by about 30-40%, and impact toughness more than twice.
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The largest amount of vanadium is contained in modern powder steels: S390, K390, CPM 15V, Vanadis 10, ASP 2060, S60V, S90V, M398, Maxamet and others. The most popular ones contain somewhat less: CPM 20CV, M390, CPM S35VN, Elmax. Thus powder steels can be divided into stainless steels with high chromium content, which most often have good wear resistance and strength, and are quite easy to work. But at the same time contain an amount of vanadium within 6%. And also on steels with a low amount of chromium and low corrosion resistance, as well as increased brittleness, but at the same time with extreme wear resistance, due to the vanadium content up to 15%. Yet any percentage of this metal in the “powder” results in positive compositional changes. The concept of “wear resistance” in powder processed steels is directly correlated with the vanadium content there. It is this metal that drives modern knife steel production technology forward.