Temperature transformations

Residual austenite is a steel structure which during cooling at martensite transformation temperature is not completely converted into martensite and remains unchanged at room temperature together with martensite. 

Terbium is reasonably stable in air. It is a silver-gray metal, and is malleable, ductile, and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1289oC. Twenty one isotopes with atomic masses ranging from 145 to 165 are recognized. The oxide is a chocolate or dark maroon color. 

Ba.inite. In a given steel, bainite microstmctures ate generally found to be both harder and tougher than peadite, although less hard than martensite. Bainite properties generally improve as the transformation temperature decreases. Lower bainite compares favorably with tempered martensite at the same hardness and can exceed it in toughness. Upper bainite, on the other hand, may be somewhat deficient in toughness as compared to fine peadite of the same hardness (33). 

In the sohd state, uranium metal exists in three aHotropic modifications. The transformation temperatures and the enthalpies of transformation are given in Table 5. The thermodynamic properties of uranium metal have been deterrnined with great accuracy and have been discussed (50). 

For maximum temperatures below 800°F, suitable ferritic steels are usually good selections. Above 800°F their loss of strength must be considered carefully and balanced against their lower thermal expansion. It should be recognized that if they are heated through the ferrite to austenite transformation temperature their behavior will become more complex and the results probably adverse. 

The normal crystal form of tin is body-centred tetragonal, but a low-temperature allotrope, grey tin , is cubic. The transformation temperature... 

In fundamental terms, the transformation temperature affects both the driving force for the decomposition of austenite and the diffusion rate of carbon. In effect, therefore, the transformation temperature alters both the rate of nucleation and the rate of growth. This in turn manifests itself in... 

At lower transformation temperatures (<770K approx.) a second reaction, the formation of bainite intervenes. Like pearlite, the bainite constituent in steels consists of a mixture of ferrite and an iron carbide and is formed by... 

Finally, at even lower transformation temperatures, a completely new reaction occurs. Austenite transforms to a new metastable phase called martensite, which is a supersaturated solid solution of carbon in iron and which has a body-centred tetragonal crystal structure. Furthermore, the mechanism of the transformation of austenite to martensite is fundamentally different from that of the formation of pearlite or bainite in particular martensitic transformations do not involve diffusion and are accordingly said to be diffusionless. Martensite is formed from austenite by the slight rearrangement of iron atoms required to transform the f.c.c. crystal structure into the body-centred tetragonal structure the distances involved are considerably less than the interatomic distances. A further characteristic of the martensitic transformation is that it is predominantly athermal, as opposed to the isothermal transformation of austenite to pearlite or bainite. In other words, at a temperature midway between (the temperature at which martensite starts to form) and m, (the temperature at which martensite... 

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