Transformation Temperature

transformation temperature

[‚tranz·fər′mā·shən ‚tem·prə·chər]
(metallurgy)
The temperature at which a change in phase occurs in a metal during heating or cooling.
The maximum or minimum temperature of a transformation temperature range.

Transformation Temperature

 

(also critical point; in Russian, Chernov point), any one of several specific critical temperatures at which a change in the phase and structure of steel occurs during heating and cooling. The most important are the two discovered by D. K. Chernov in 1868, which he called points a and b; the determination of their values and relative positions on the temperature scale marked the beginning of the scientific heat treatment of steel and was of enormous practical value.

According to Chernov the significance of point a (dark cherry temperature color) is that when steel is heated to a temperature below point a, it cannot be hardened no matter how rapidly it is cooled. For point b Chernov gave the following evaluation: when steel is heated to a temperature below point b, its structure does not change and a fracture retains its earlier form. According to Chernov, point a is the temperature above which steel must be heated in order to be hardened, and point b is the temperature above which heating tends to refine a coarse-grain structure. Later, in 1878, Chernov proposed point d (he defined point c as the melting point of steel), with a value of approximately 200°C, as the temperature to which steel must be rapidly cooled in order to achieve full hardening.

In modern representations, point a (now designated as A1) corresponds to the eutectoid temperature. Point b is usually identified with the temperature, now designated as A3, at which the dissolution of ferrite in austenite is completed when steel is heated. According to Chernov, steel heated above point b acquires after cooling a fine-grain structure, which thus determines the value of the point for the heat treatment of steel. Since in a number of cases heating above A3 is not followed by the refinement of a coarse crystalline structure, the unqualified identification of point b with A3 is apparently incorrect. Point d is now known as the temperature of martensitic transformation when steel is hardened, usually designated by Ms.

REFERENCES

D. K. Chernov i nauka o metallakh. Leningrad-Moscow, 1950.
Sadovskii, V. D. Strukturnaia nasledstvennost’ v stali. Moscow, 1973.

V. D. SADOVSKII

References in periodicals archive ?
To study the thermal behavior and identification of the phase transformation temperature of the as prepared manganese oxide precursor particles, the latter were heated in the TGA/DTA analyzer (Diamond TGA/DTA Perkin Elmer) in the temperature range of 30-800 AdegC in the flow of air at a heating rate of 5 AdegC min-1.
5, a, the start transformation temperature (As) decreases from 1010.
Defined as irreversible and usually unpredictable dimensional changes during the process, distortion occurs when heating the work piece above the transformation temperature results in it losing the inherent strength it possesses at room temperature, often causing it to distort under its own weight.
Defined as irreversible and usually unpredictable dimensional changes during the process, distortion occurs when heating the workpiece above the transformation temperature results in it losing the inherent strength it possesses at room temperature, often causing it to distort under its own weight.
Alloying elements are added to stabilize either [alpha] and [beta] phase, by changing [beta] transformation temperature.
The result is that the surface moving at the lower rate of speed absorbs much more heat that is generated at the point of contact, with the risk of exceeding the transformation temperature of the material.
The fluctuation in temperature range from lower transformation temperature to austenitizing temperature increases the importance of material selection and the significance of subsequent fabrication, welding and heat treatment.
The robot's limbs transform with increasing temperature at discrete temperatures, whereas in conventional shape memory technology this is limited to only one transformation temperature.
With glasses, temperatures near the transformation temperature ([T.

Full browser ?