Isothermal transformation diagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic scale). They are generated from percentage transformation-vs time measurements, and are useful for understanding the transformations of an alloy steel at elevated temperatures.
An isothermal transformation diagram is only valid for one specific composition of material, and only if the temperature is held constant during the transformation, and strictly with rapid cooling to that temperature. Though usually used to represent transformation kinetics for steels, they also can be used to describe the kinetics of crystallization in ceramic or other materials. Time-temperature-precipitation diagrams and time-temperature-embrittlement diagrams have also been used to represent kinetic changes in steels.
Isothermal transformation (IT) diagram or the C-curve is associated with mechanical properties, microconstituents/microstructures, and heat treatments in carbon steels. Diffusional transformations like austenite transforming to a cementite and ferrite mixture can be explained using the sigmoidal curve; for example the beginning of pearlitic transformation is represented by the pearlite start (Ps) curve. This transformation is complete at Pf curve. Nucleation requires an incubation time. The rate of nucleation increases and the rate of microconstituent growth decreases as the temperature decreases from the liquidus temperature reaching a maximum at the bay or nose of the curve. Thereafter, the decrease in diffusion rate due to low temperature offsets the effect of increased driving force due to greater difference in free energy. As a result of the transformation, the microconstituents, pearlite and bainite, form; pearlite forms at higher temperatures and bainite at lower.
Austenite is slightly undercooled when quenched below Eutectoid temperature. When given more time, stable microconstituents can form: ferrite and cementite. Coarse pearlite is produced when atoms diffuse rapidly after phases that form pearlite nucleate. This transformation is complete at the pearlite finish time (Pf).
However, greater undercooling by rapid quenching results in formation of martensite or bainite instead of pearlite. This is possible provided the cooling rate is such that the cooling curve intersects the martensite start temperature or the bainite start curve before intersecting the Ps curve. The martensite transformation being a diffusionless shear transformation is represented by a straight line to signify the martensite start temperature.
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Isothermaltransformationdiagrams (also known as time-temperature-transformation (TTT) diagrams) are plots of temperature versus time (usually on a logarithmic...
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Austenitization and Pre-Deformation on the Kinetics of the Isothermal Bainitic Transformation". Metall Mater Trans A. 40 (6): 1355–1366. Bibcode:2009MMTA...
mass between the thermodynamic system and its environment. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only...
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at 723 °C (1,333 °F) and 0.76 wt% carbon. A peritectoid transformation is a type of isothermal reversible reaction that has two solid phases reacting with...
of isothermaltransformations being used in industry and he began to conceive new experiments Further research into the isothermaltransformation of steels...
UCS is mostly used to calculate correlated color temperature, where the isothermal lines are perpendicular to the Planckian locus. As a uniform chromaticity...
characterizing the Carnot cycle. Heat transfer in the isotherm steps (isothermal expansion and isothermal compression) of the Carnot cycle was found to be...
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature...
by cooling water, is necessary. In the ideal case the compression is isothermal. The average heat flow to the surroundings is Q̇. Since the system is...
achieve perfect isothermal compression. For an isothermal process, n {\displaystyle n} is 1, so the value of the work integral for an isothermal process is:...
constant. While heat can always be fully converted into work in a reversible isothermal expansion of an ideal gas, for cyclic processes of practical interest...
temperature based on MacAdam's (u,v) Uniform chromaticity transformation of the CIE diagram". JOSA. 53 (8): 999. Bibcode:1963JOSA...53..999K. doi:10.1364/JOSA...
Determining heat transfer in a system by measuring its other properties Isothermal microcalorimetry – Measuring versus elapsed time the net rate of heat...
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available to perform work. However, this is incorrect. For instance, in an isothermal expansion of an ideal gas, the internal energy change is Δ U = 0 {\displaystyle...
under a symmetry transformation (such as translation or rotation), so that any pair of outcomes differing only by that transformation have the same probability...
associated terms in the energy balance is null, thus rendering the transformation isoenthalpic. The lifting of a relief (or safety) valve on a pressure...
conjugate variable to entropy, thus the conjugate process would be an isothermal process, in which the system is thermally "connected" to a constant-temperature...
underlying this technique is that when the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it...
the system will change in a way that is not easily predictable. Some "transformation energy" will be used as the molecules of the "working body" do work...
relative to the inert reference. Thus, a DTA curve provides data on the transformations that have occurred, such as glass transitions, crystallization, melting...
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