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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
But the grain size and grain distribution of the silica sand also has an influence on the surface behavior, because a higher degree of uniformity leads to higher stresses, since all silica grains pass through the transformation temperature at the same time.
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.
Alloying elements either increases or decreases the transformation temperature depending on whether they are hcp (Cr, Re) or fcc (Ni, Fe) stabilisers.
They found that phase stability is largest where the atomic misfit is large, and the phase transformation temperature shifts to lower temperature.
Three Q&P sequences were carried out on the experimental steel with a reduced martensite transformation temperature. They involved various soaking times and cooling rates of 16 and 1[degrees]C/s.
In low temperature, the NiTinol wire is soft and can easily change its shape, it has ability to return to its original shape, after activated above finish temperature (transformation temperature).
5, a, the start transformation temperature (As) decreases from 1010.05 K to 999.28 K with increasing Mn concentration.
Thermomechanical treatments could maintain the alloy in the martensite phase, R-phase, or mixed form by altering the transformation temperature and consequently changing the characteristics of the alloy [4, 7].
So far, the addition of tantalum has shown a significant effect on the microstructure, mechanical properties, and phase transformation temperature of shape memory alloys [23-25], due to its aptitude to reduce the transformation temperature, increase the thermal stability, and improve the strain recovery ([[epsilon].sub.reco]) and residual strain ([[epsilon].sub.res]) during thermal cycling.
Meanwhile, the [beta] transformation temperature of Ti-5Al-1Fe is 1,283 K [13].
At temperatures higher than tetragonal to monoclinic transformation temperature, the cracks again emerge due to a volume increase in the crystallization transformation.

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