Alpha-ferrite

Heating iron to 907°C causes a change from BCC (alpha, ferrite) iron to the FCC (gamma, austenite) form. 

Alpha-ferrite (a-ferrite, bcc). Sensu stricto and historically, ferrite consists of a solid solution of carbon inside a body-centered cubic crystal lattice in alpha-iron. As mentioned in Section 2.1.2, the solubility of carbon in alpha-iron is extremely low, ca. 0.01 wt.% C at ambient temperature, and reaches only 0.025 wL% C at 723 C. Therefore, at room temperature under conditions of equilibrium, any carbon present in excess of that small amount will exsolute in the form of cementite. Due to this low carbon content, some textbooks treat the ferrite phase substantially as pure iron, but this view must be discontinued to avoid confusion. Usually, the ferrite of an alloyed steel may contain in solid solution appreciable amounts of other elements ab extenso, any solid solution of which alpha-iron is the solvent is called ferrite (i.e., a solid solution of any element in alpha-iron). Alloying elements that stabilize ferrite are listed in Table 2.11. 

Beta-ferrite (P-ferrite, bcc). Like alpha-ferrite, beta-ferrite consists of a solid solution of any element in body-centered cubic beta iron. 

Aj Temperature at which austenite and alpha-ferrite coexist temporarily and above which only austenite exists. 

A j Temperature at which the transformation alpha-ferrite-austenite is completed upon heating. A 3 Temperature at which the transformation of austenite into alpha-ferrite initiates upon cooling. 

Ferrite Solid solution of carbon in alpha iron (bcc). 

Ferrite. This is practically pure iron and cun exist in magnetic alpha-iron lorm in iron, with up 10 O.X.5rf carbon. Fertile exists ai room temperature and up lo aboul dKFC in the absence of carbon. Its upper Intiii of existence is lowered progressively lo about 725 C as the carbon content increases up to O.X.Vr. Ferrite cannot dissolve carbon, is soli and ductile, and lias poor abrasive resistance. 

Examples of a few are alpha cellulose, ash, calcium carbide, calcium carbonate, carborundum, channel black, china clay, coral, coke dust, diatomaceous earth, dolomite [double carbonate of lime and magnesia filler having the formula (CaCOg) and (MgCOg)], ferrite, flint, fixller s earth, glass spheres, hemp, keratin, lampblack, leather-dust, macerate... 

The technology base for the LFR is primarily derived from the Pb-Bi liquid alloy-cooled reactors employed by the Russian Alpha class submarines. Technologies developed from the integral fast reactor metal alloy fuel recycle and refabrication development, and from the advanced liquid metal reactor (ALMR) passive safety and modular design approach, may also be applicable to the LFR. The ferritic stainless steel and metal alloy fuel developed for sodium fast reactors may also be adaptable to the LFR for those concepts with reactor outlet temperatures in the range of BSO C. 

Alpha-iron (a-Fe). Between room temperature and a transition temperature of 769°C, pure iron exhibits a body-centered cubic (bcc) crystal lattice (a = 286.645 pm at 25°C). Alpha-iron is a soft, ductile metal with a density of 7875 kg.m l Alpha-iron is also ferromagnetic, with a saturation magnetization at room temperature of 220 A-m -kg , and the cubic anisotropy constants are = 4.7 x 10 J-m and = 1.5 - 3.0 x 10 J m Carbon exhibits a poor solubility in alpha-iron with a maximum content of 0.025 wt.% C at 723°C. It is important to note that the word ferrite describes a solid solution of carbon into alpha-iron, though it is sometimes improperly used to describe alpha-iron (Section 2.1.9) ... 

Jiang et al. (1992) investigated the alpha prime precipitation in aged duplex stainless steel. Samples (65% ferrite, 35% austenite) were aged at 450°C for 100, 1000, and 5000 h. The electrochemical behavior of the aged sample was examined in 0.1 - 0.5 M... 

Steels which contain both the body-centered cubic alpha-phase and the face-centered cubic gamma-phase, are called Duplex Steels. Austenitic ferritic steels containing about 5% or more delta-ferrite show a higher resistance than... 

Answer by Author A good discussion of this problem appears in R. M. Bozorth s Ferromagnetism, D. Van Nostrand and Co.. Princeton, New Jersey (1956) p. 146. Temperature and cold-work are interrelated variables in that both lowered tempera-mres and cold-work promote the transformation of paramagnetic austenite to ferromagnetic martensite (also called "alpha" or ferrite by other investigators). In this sense, magnetic permeability depends on both variables. 

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