Alloying (metallurgy)

History

Doping has become purposefully used relatively recently. This was partly due to technological difficulties. Alloying additives simply burned out using traditional steel technology.

It is noteworthy that the first steels that a person met were naturally alloyed steels. Even before the beginning of the Iron Age , meteorite iron was used, containing up to 8.5% nickel ^[1] .

Naturally alloyed steels made from ores originally rich in alloying elements were also highly valued ^[2] . The increased hardness and toughness of Japanese swords with the ability to ensure the sharpness of the edge, possibly due to the presence of molybdenum in steel ^[3] .

Modern views on the effect on the properties of steel of various chemical elements began to take shape with the development of chemistry in the second quarter of the XIX century ^[3] .

Apparently, the invention of steel containing 1.85% carbon , 9% tungsten, and 2.5% manganese could be considered the first successful use of targeted alloying. Steel was intended for the manufacture of metal cutting machine tools and was the prototype of the modern line of high-speed steels . Industrial production of these steels began in 1871.

It is believed that the first alloy steel of mass production was Hadfield Steel , discovered by the English metallurgist Robert Abbot Hadfield in 1882 ^[3] . Steel contains 1.0 - 1.5% carbon and 12 - 14% manganese, has good casting properties and wear resistance . Without special changes in chemical composition, this steel has survived to the present.

The influence of alloying elements

To improve the physical, chemical, strength and technological properties, metals are alloyed by introducing various alloying elements into their composition. For alloying steels, chromium, manganese, nickel, tungsten , vanadium , niobium , titanium and other elements are used. Small cadmium additives in copper increase the wear resistance of wires, zinc additives in copper and bronze increase strength, ductility, and corrosion resistance. Alloying titanium with molybdenum more than doubles the temperature limit of operation of the titanium alloy due to a change in the crystal structure of the metal. ^[4] Alloyed metals may contain one or more alloying elements, which give them special properties.

Alloying elements are introduced into steel to increase its structural strength. The main structural component in structural steel is ferrite , which occupies at least 90% by volume in the structure ^[5] . Dissolving in ferrite, alloying elements strengthen it. The hardness of ferrite (in the state after normalization) is most strongly increased by silicon, manganese and nickel. Molybdenum, tungsten and chromium are less affected. Most alloying elements, hardening ferrite and having little effect on ductility , reduce its impact strength (with the exception of nickel). The main purpose of alloying:

• increasing the strength of steel without the use of heat treatment by hardening ferrite by dissolving alloying elements in it;
• increase in hardness, strength and toughness as a result of increasing the stability of austenite and thereby increasing hardenability;
• imparting special properties to steel, of which heat resistance and corrosion resistance are of particular importance for steels used for the manufacture of boilers, turbines and auxiliary equipment.

Alloying elements can dissolve in ferrite or austenite, form carbides , give intermetallic compounds, settle in the form of inclusions without interacting with ferrite and austenite, as well as with carbon. Depending on how the alloying element interacts with iron or carbon, it affects the properties of steel in different ways. All elements are more or less dissolved in ferrite. The dissolution of alloying elements in ferrite leads to the hardening of steel without heat treatment. In this case, the hardness and tensile strength increase, and the toughness usually decreases. All elements that dissolve in iron alter the stability of ferrite and austenite. The critical points of alloy steels are shifted depending on which alloying elements and in what quantities are present in it. Therefore, when choosing temperatures for quenching , normalization, and annealing or tempering , the shift of critical points must be taken into account.

Manganese and silicon are introduced in the process of steelmaking for deoxidation , they are technological impurities. Manganese is introduced into steel up to 2%. It is distributed between ferrite and cementite. Manganese significantly increases the yield strength, cold brittleness threshold, hardenability of steel, but makes steel sensitive to overheating. In this regard, carbide-forming elements are introduced into the steel to grind grain with manganese. Since the content of manganese in all steels is approximately the same, its effect on steel of different compositions remains imperceptible. Manganese increases strength without reducing the ductility of steel.

Alternative version of the above:

Manganese and silicon are constant companions in almost any steel, since they are specially introduced during its production. Silicon, along with manganese and aluminum is the main deoxidizer of steel. Manganese is also used to “bind” sulfur found in steel and to eliminate the phenomenon of red brittleness . The content of elements is usually in the range of 0.30 - 0.70% Mn, 0.17-0.37% Si and about 0.03% Al. Within these limits, they are called technological impurities and are not alloying elements. A special introduction of manganese, silicon and aluminum of the above ranges to give steel certain consumer properties will already be alloying ^[6] .

Silicon is not a carbide forming element, and its amount in steel is limited to 2%. It significantly increases the yield strength and strength of steel and, with a content of more than 1%, reduces viscosity, ductility and increases the cold brittleness threshold. Silicon is not structurally detected, since it is completely soluble in ferrite , except for that part of silicon which, in the form of silicon oxide, did not manage to surface in the slag and remained in the metal in the form of silicate inclusions.

Alloy Steel Marking

The brand of alloyed high-quality steel in Russia consists of a combination of letters and numbers indicating its chemical composition. Alloying elements have the following designations: chromium (X), nickel (H), manganese (G), silicon (C), molybdenum (M), tungsten (B), titanium (T), tantalum (Ta), aluminum (Yu) , vanadium (F), copper (D), boron (P), cobalt (K), niobium (B), zirconium (C), selenium (E), rare earth metals (H). The numbers after the letter indicate the content of the alloying element in percent. If the numbers are not indicated, then the alloying element contains 0.8-1.5%, with the exception of molybdenum and vanadium (the content of which in steels is usually up to 0.2-0.3%) As well as boron (in steel with the letter P it should be up to 0.010% ) In structural high-quality alloy steels, the first two digits indicate the carbon content in hundredths of a percent ^[7] .

Example: 03X16H15M3B - high alloyed high-quality steel that contains 0.03% C, 16% Cr, 15% Ni, up to 3% Mo, up to 1% Nb

Separate groups of steels are designated slightly differently:

• Ball-bearing steels are marked with letters (SH), after which indicate the chromium content in tenths of a percent;
• High-speed steels (complex alloyed) are indicated by the letter (P), the next figure indicates the percentage of tungsten;
• Automated steels are indicated by the letter (A) and the numbers indicate the carbon content in tenths of a percent.

• Become
  • Chrome steel ;
  • Well-known steels ШХ15 (outdated brand designation) used as material for bearings;
  • The so-called " stainless steels ";
  • Steel and alloys alloyed with molybdenum, tungsten, vanadium;
  • Heat resistant steels and alloys.
• Aluminum
• Bronze
• Brass
• Glass

• Alloy
• Impurity
• Ligature (metallurgy)
• Non-ferrous metallurgy
• Ferrous metallurgy

• "Doping" - an article in the "Chemical Encyclopedia"
• “Alloying” - an article in the “Metallurgical Dictionary”
• “Doping” (inaccessible link) - article in the “Encyclopedia of Cyril and Methodius”