Austenitic phase

Fig. 19. Effect of cooling rate on structure of a eutectoid steel. = austenitizing temperature > = austenite phase.

The austenite phase which can contain up to 1.7 wt% of carbon decomposes on cooling to yield a much more dilute solution of carbon in a-iroii (b.c.c), Fenite , together with cementite, again rather diaii the stable carbon phase, at temperatures below a solid state eutectoid at 1013 K (Figure 6.3). 

Aurantin, molecular formula and structure, 5 91t Ausimont, 7 641 Austempering, 23 287 Austenite, 23 272, 273, 275 decomposition of, 76 197-198 grain size of, 23 276-277 in hardening of steels, 76 196-197 phase transformations in, 23 277 transformation rates of, 23 282—283 Austenite phase, in martensite... 

When anstenite is cooled nnder more rapid conditions, a compound called bainite is produced. Bainite is a noneqnilibrinm prodnct that is similar to pearlite, but consists of a dispersion of very small FesC particles between the ferrite plates. Bainite formation is favored at a high degree of snpercooling from the austenite phase, whereas pearlite forms at low degrees of supercoohng, or more equilibrium cooling. 

Figure 3.6 Shape-memory alloys transform from (a) a partially ordered, high-temperature austenitic phase to (b) a mixed austenite-martensite low-temperature state to (c) an ordered mixed-phase state under deformation.

The best-known eutectoid reaction is that which occurs in steel where the austenite phase, stable at high temperatures, transforms into (he eutectoid structure known as pcarlitc In this transformation, the austenite phase, containing 0.8% carbon in solid solution, transforms to a mixture of ferrite (nearly pure body-centered cubic irom anti iron-carbide (Fe-.Ct. Al atmospheric pressure, the equilibrium temperature for this reaction is 723 C. This temperature is the eutectoid temperature... 

In Fig. 9 the compositional dependence is shown of the latent heat Q of the martensite-austenite phase transition. It is evident that Q strongly increases with increasing x. These results are in good agreement with a recently published one [26],... 

As evident from Fig. 4, the Curie temperature of the austenitic phase decreases upon substitution of Mn for Ni. This is due to the fact that upon such a substitution a number of Ni atoms with smaller, as compared to Mn, magnetic moment increases. A similar tendency presumably takes place for a hypothetical Curie temperature of the martensitic phase. This follows from the fact that, as is seen from Fig. 3, in the low-temperature martensitic phase the magnetization of the Ni2+a Mni a Ga alloys with high Ni excess decreases more rapidly with increasing temperature. 

The collected data allow us a rough estimation of the hypothetical Curie temperature of the martensitic phase. Figure 10 shows temperature dependencies of the reduced spontaneous magnetization m = Ms(T)/Ms(0) of the alloys as a function of reduced temperature t = T/Tc. It is seen that the magnetization of the austenitic phase and... 

The Cu contents promotes the generation of fine grained austenitic phase and the corrosion resistance. 

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