Steel ligation. Auxiliary alloying elements
Alloying(from Latin ligo - bind, connect), the introduction of additives into metals, alloys and semiconductors to give them certain physical, chemical or mechanical properties. Materials that have been subjected to alloying are called alloyed. These include alloyed steels and cast irons, alloyed non-ferrous metals and alloys, alloyed semiconductors. For alloying, metals, non-metals (C, S, P, Si, B, N 2, etc.), ferroalloys (see Iron alloys) and alloys are used - auxiliary alloys containing an alloying element. For example, the main alloying elements in steels and cast irons are Cr, Ni, Mn, Si, Mo, W, V, Ti, Al, Nb, Co, Cu, in aluminum alloys - Si, Cu, Mg, Ni, Cr, Co, Zn, in magnesium alloys - Zn, Al, Mn, Si, Zr, Li, in copper alloys - Zn, Sn, Pb, Al, Mn, Fe, Ni, Be, Si, P, in titanium alloys - Al , Mo, V, Mn, Cu, Si, Fe, Zn, Nb.
Alloying is a qualitative concept. Every metal or alloy contains inevitable impurities due to the manufacturing process or raw materials. They are not considered alloying, since they were not introduced specifically. For example, Ural iron ores contain Cu, Kerch iron ores contain As, steels obtained from these ores also contain impurities of Cu and As, respectively. The use of tinned, galvanized, chromed and other scrap metal leads to the fact that impurities of Sn, Zn, Sb, Pb, Ni, Cr, etc. get into the resulting metal.
When alloying metals and alloys, solid solutions of substitution, interstitial or subtraction, mixtures of two or more phases (for example, Ag in Fe), intermetallic compounds, carbides, nitrides, oxides, sulfides, borides and other compounds of alloying elements with the alloy base or between yourself.
As a result of alloying, the physicochemical characteristics of the original metal or alloy and, above all, the electronic structure change significantly. Alloying elements affect the melting point, the region of existence of allotropics. modifications and kinetics of phase transformations, the nature of crystal lattice defects, the formation of grains and fine crystal structure, the dislocation structure (the movement of dislocations is hampered), heat resistance and corrosion resistance, electrical, magnetic, mechanical, technological alloying (for example, weldability, grindability, machinability) , diffusion and many other properties of alloys.
Alloying is divided into bulk and surface. With volumetric alloying, the alloying element is, on average, statistically distributed in the volume of the metal. As a result of surface alloying, the alloying element is concentrated on the surface of the metal. Alloying with several elements at once, a certain content and ratio of which makes it possible to obtain the required set of properties, called. complex alloying and resp. alloys - complex alloyed. For example, as a result of alloying austenitic chromium-nickel steel with tungsten, its heat resistance increases by 2-3 times, and when using W, Ti and other elements together - by 10 times.
Conventionally, the following concepts are distinguished: alloying, microalloying and modification. When alloying, 0.2-0.5% by weight or more of the alloying element is introduced into the alloy, when microalloying - most often up to 0.1%, when modifying - less than during microalloying, or the same amount, however, the problems solved by microalloying and modification, different. Microalloying effectively affects the structure and energy state of grain boundaries, and it is assumed that two strengthening mechanisms will be implemented in the alloy - due to solid solution alloying and as a result of dispersion hardening. Modification contributes to the refinement of the structure and changes in geome during the crystallization process. shape, size and distribution of non-metallic inclusions, changing the shape of eutectic precipitates, generally improving mechanical properties. For microalloying, elements with noticeable solubility in the solid state (more than 0.1 at.%) are used; elements with negligible solubility are usually used for modification ()