Alloying elements in steel

Silicon s atomic structure makes it an extremely important semiconductor. Highly purified silicon, doped with such elements as boron, phosphorus, and arsenic, is the basic material used in computer chips, transistors, sUicon diodes, and various other electronic circuits and electrical-current switching devices. Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, brass, and bronze. 

Aluminum is not commonly used as an alloying element in steel to improve oxidation resistance, as the amount required interferes with... 

Table I. Vapor Pressures of Alloying Elements in Steel I.8OO a.

Nickel is used throughout industry because of its excellent corrosion resistance. In addition to itr+us37- oe/oe" nn< cladding material to provide corrosion resistance to tanks and production vessel surfaces, nickel is used as an alloying element in steel production. Nickel is resistant to attack by NaOH and other alkali solutions, but is not compatible with ammonium hydroxide. Nickel is resistant to corrosion by sodium chloride solutions, but is corroded severely by iron, copper- and mercury chloride salts. Also, nickel has excellent corrosion resistance to most organic acids. Some of the common nickel alloys are described below ... 

One of the principal functions of alloying elements in steel, such as manganese, chromium, nickel, molybdenum, etc., is to increase the hardenabilitv. Whereas prodigious amounts of expensive alloys were formerly used to insure full hardening, especially in medium and heavy sections, wartime shortages focused attention on the use of as little alloy as possible within the hardenabilitv requirements. A large number of steels were developed containing relatively small additions of a number ol elements, and a number of these steels hav e continued in use. 

Of the common alloying elements in steel, molybdenum is the niiisl effective in increasing creep—rupture strength, and the carbon— molybdenum steels generally have more than twice the creep—rupture strength of plain carbon steel at the same temperature. The most commonly used steels for high temperature service contain from 0.5 to 1.5% molybdenum. 

Requirements are placed on alloying elements in steel to control strength, weldability, and notch toughness. 

There are five principal reasons for the use of molybdenum as an alloying element in steels and cast irons. 

The application of tungsten metal which, at the beginning of the 20th century, was used only as a filament in incandescent bulbs and as alloying element in steel, as well as of its alloys, is nowadays very widespread and covers quite different fields such as lighting, electronics, high-temperature technology, medicine, aviation, military uses, sports, and so on. 

E. C. Bain and H. W. Paxton, Alloying Elements in Steel, ASM International, Materials Park, Ohio, 1961. 

TDA has provided useful information on the tempering process and iie influence of individual alloying elements in steel (15). Complications irise due to the fact that while the decomposition of martensite produces a. ontraction, decomposition of any retained y-iron is accompanied by expan-... 

The ferrous metals, which include Co, Ni, Cr, Mn, and Mo, besides Fe, all have line-rich spectra and with the exception of iron all are used as alloying elements in steels. No specific interference effects have been observed for Fe, Co, or Ni for Cr and Mn the effects are only slight for Mo they can be considerable. The tendency to exhibit interference effects corresponds to the tendency to form oxides in the flame and is, therefore, predominantly due to the formation of nonvolatile compounds and may be eliminated by using releasing elements. Thus, for example, the depressive effect of Si on Cr and Mn may be eliminated by the addition of Ca or Sr to the solution sprayed. 

Carbon steels and stainless steels are the most common construction materials for equipment used in the manufacture, storage, and transportation of sulfuric acid. Anodic protection was successfully used to control the corrosion of the various equipments made of these materials in this acid over a wide range of temperatures. While the corrosion rates of carbon steels in sulfuric acid are mainly functions of temperature, velocity, and acid concentration and purity, particularly the iron content, these rates are greatly affected by minor alloying elements in steel, particularly copper. The corrosion rates of steel in 77 to 100% concentrations are in the range of 20 to 40-mils per year (mpy) at 24 °C [14]. 

The Cr-Fe-Mo system has been studied extensively. Bofli Cr and Mo are important elements used in steels, in the past and in the present days. Knowledge of die phase diagram of such a system is therefore of significant interest, especially now, when the number and amount of alloying elements in steels and other alloys is increasing, and intermetallic phases are playing a more important role. 

E.C. Bain, H.W. Paxton Alloying elements in steel, (Handbook American Society of Metals, Park, Ohio, 1966). 

Phase relations in the C-Fe-W system are of great interest above all because of the importance of tungsten as alloying element in steels. Therefore constitution of this system has been studied quite intensively. Other important aspects of this subject, in particular the dissolution of iron carbides during austenitization of tungsten steels, phase transformations of carbides as well as diffusion interaction of carbides with iron and steels also attract attention of investigators widely. Details of experimental studies of phase relations, crystal strac-tures and thermodynamics as well as applied techniques are presented in Table 1. 

Small amounts of alloying elements in steel can have a significant beneficial effect on corrosion in the atmosphere. Copper-bearing steels (0.2 % copper, minimum) have long been used for this purpose. In the HSLA weathering steels, small additions of elements such as chromium, silicon, copper, nickel, and phosphorus are used to achieve even greater resistance to atmospheric corrosion. 

In the periodic table, Figure 17.1, all the elements belonging to groups 3-12 are called transition dements. Many of them are important in technical applications as for instance alloying elements in steels and superalloys. 

FigMre 9.34 The dependence of eutectoid temperature on alloy concentration for several alloying elements in steel. 

From Edgar C. Bain, Functions of the Alloying Elements in Steel, 1939. Reproduced by permission of ASM International,... 

Adapted from Edgar C. Bain, Functions of the Alloying Elements in Steel, 1939 and R. A. Grange, C. R. Hribal, and L. F. Porter, Metall. Trans. A, Vol. 8A. Reproduced by permission of ASM International, Materials Park, OH.)... 

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