The JMAK (Johnson-Mehl-Avrami-Kolmogorov) fit by is used for the simulation , the parameters of which are set by the TTT-diagram

The diagram consists of two curves corresponding to the origin of the transformation (volume fraction of the daughter phase ξmin) and its completion (volume fraction of the daughter phase ξmax). The diagram shows how time it will take for the share of the child phase to increase from ξmin before ξmax at a given temperature. Since the typical value ​​given in the reference literature for ξmin And ξmax are 1 and 99% or 5 and 95%, respectively, then the diagram can be used to estimate the total time of the phase transformation at a given temperature.

When setting data, pay attention to the following:

•Для долей фаз на кривых должно выполняться соотношение 0% < ξmin < ξmax < 100%.

•TTT curves are given in tables, which may have a different amount of rows, however, the maximum and minimum temperature for both curves must match. Also, the start time and duration (distance between curves) of the transformation must be greater than 0 for all temperatures (i.e. the curves must not intersect). If the specified restrictions are not met, an appropriate error message appears.

•TTT curves are not extrapolated from temperature.

•When simulation steel quenching processes , this transformation kinetic model is usually used to comment the kinetics of the transformation of austenite into ferrite, pearlite and bainite.

For various materials, TTT diagrams can be found in the reference literature:

1.Popova L.E., Popov A. A. austenite Transformation Diagrams in Steels and Beta Solution in Titanium Alloys: A Thermist's Handbook. 3 ed., revised. and additional M.: Metallurgy, 1991.

2.Atlas of Time-Temperature Diagrams for Irons and Steels / Ed. by GF Vander Voort. ASM International, 1991.

3.Atlas zur warmebehandlung der stahle / F. Wever, A. Rose., W. Peter, W. Strassburg, L. Rademacher. Dusseldorf: Verlag Stahleisen MBH, 1961.

To simulation diffusionless phase transformation, for example, austenite to martensite during steel quenching , the Koistinen-Marburger fit by is used, described by the formula

•Если известна температура начала мартенситного превращения TMS, а также доля дочерней фазы, например 50%, для температуры TM50< TMS, и доля дочерней фазы, например 90%, для температуры TM90<TM50<TMS то коэффициенты ψ1, ψ2 и ψ3 могут быть определены из системы уравнений

•Если известна температура начала мартенситного превращения TMS, а также доля дочерней фазы, например 50%, для температуры TM50<TMS, то ψ1 = 0, а коэффициенты ψ2 и ψ3 могут быть определены из системы уравнений

•If only the temperature of the origin of martensitic transformation is known TMS, then the formula is used to simulation

For the convenience of the user, these calculations are performed auto, and only the temperature and fractions of the child phase need to be set.

The JMAK fit by is used for the simulation , but the transformation kinetics is described by the formula

The Fit by is recommended to be used for simulation steel tempering processes , i.e. for the phase transformation of martensite into tempering martensite.

parameters Value D0, Q And m for some carbon tool steels can be taken from the work of Zhang Z., Delagnes D., Bernhart G. Microstructure evolution of hot-work tool steels during tempering and definition of a kinetic law based on hardness measurements // Materials Science and Engineering A. Vol. 380. 2004. P. 222-230.

The Fit by can be used to comment the kinetics of both diffusion and martensitic transformations.

The Comment of the fit by is given in the work of Leblonde JB, Devaux J. A new kinetic model for anisothermal metallurgical transformations in steels including the effect of austenite grain size // Acta metal. 1984. Vol. 32(1). P. 137-146.

Пользователю необходимо таблично задать функции τ=f(T)>0 и

В случае закалки сталей, Leblonde J.B. и Devaux J. предлагают задавать значения для всех превращений, кроме превращения аустенита в бейнит.

Функция ξmax=f(T) представляет собой равновесную объемную долю фазы продукта.