Ferrite Property Model Settings

The Ferrite Property Model, available with the Property Model Calculator and the Steel Model Library, calculates the thermodynamics and isothermal kinetics of proeutectoid ferrite forming from austenite in hypoeutectoid steels.

About the Ferrite Property Model

For an example, see PM_Fe_09: Fe-C-Ni Ferrite.

Included Elements and Important Notes

  • Austenite must contain at least Fe and C for this model to function.
  • Elements that are quite soluble in both austenite and ferrite—Mn, Ni, Si, Al, Co, Cr, and Mo—have their effects on overall kinetics assessed.
  • Cu and strong carbide-formers—W, V, Nb, Ta, Ti, and Zr—can be included, but only to a certain extent not to cause phases other than austenite and ferrite to form at the calculation temperature. Otherwise, the model calculation may give unrealistic results or even fail. If carbide is expected to form at an austenitizing temperature, use the setting Equilibrium composition at austenitizing temperature for Austenite composition from, then enter an austenitizing temperature.

Elements not listed above are excluded in mass percent from the austenite composition used to calculate the transformation.

For the Ferrite, Bainite, and Pearlite Property Models, it is also useful to review the Recommended Composition Ranges for Steel Models.

To run calculations with the Steel Models requires a valid maintenance license plus licenses for both the TCFE (version 9 and newer) and MOBFE (version 4 and newer) databases. Also see our website to learn more about the Steel Model Library and other related examples.

Configuration Settings

These settings are found on the Property Model Calculator when Ferrite is selected under Steel Models.

When working in the Configuration window, click the Description tab for more information about the Model.

For the details about the Condition Definitions, Calculation Type, Timeout in minutes, Parallel Calculation, and other calculation associated settings, see Property Model Calculator: Configuration Window Settings.

Select an option from the Austenite composition from list:

  • Nominal composition uses the system composition as austenite composition.
  • Equilibrium composition at austenizing temperature. Select to enter an Austenitizing temperature. The austenite composition is determined from an equilibrium calculation at the austenitizing temperature (if austenite is stable). This option is useful when austenite coexists with other phase(s), e.g. primary carbide, before the transformation(s) being calculated starts. But the Model only considers the effect of other phase(s) on austenite composition.

This setting is available when Equilibrium composition at austenitizing temperature is selected from the Austenite composition from list.

Enter an Austentizing temperature in the field. The unit is the same as that selected under Condition Definitions.

Enter the Grain size of the austenite in micrometers (μm). The default is 100 μm.

Select a Growth mode: Orthoequilibrium (OE), Paraequilibrium (PE), Negligible-partitioning local equilibrium (NPLE), Orthoprecipitate (OP), or Paraprecipitate (PP). This defines the compositions on the two sides of the ferrite-austenite interface and therefore affects growth rate.

For definitions of these modes, see About the Ferrite Property Model.

Enter a Phase addition in J/mol. This applies a Gibbs energy shift to ferrite.

Click to select the Skip time integration checkbox to skip this step in the calculations. Time integration is required for calculating ferrite start/half/finish times, but is usually time-consuming. Skipping time integration allows you to get the other result quantities more quickly.

Custom Parameters

Select the Custom parameters checkbox to choose to set more advanced settings as listed below.

  • Site density, Edge surface energy, and Epsilon are for calculating grain-boundary nucleation rate (see [1988Lan] for definition and details).
  • M0 and Q are to define an interfacial mobility in the Arrhenius equation.

This setting is available when Custom parameters is selected. Enter a Site density in 1/m2.

This setting is available when Custom parameters is selected. Enter an Edge surface energy in J/m2.

This setting is available when Custom parameters is selected. Enter a value for Epsilon in J/m2.

This setting is available when Custom parameters is selected. Enter a value for M0 in m mol/(Js). This is the pre-exponential factor for interfacial mobility.

This setting is available when Custom parameters is selected. Enter a value for Q in J/mol. This is the activation energy for interfacial mobility.

This setting is available when Custom parameters is selected, and is used for time integration.

Enter the Maximum phase fraction change (absolute) in a time step.

This setting is available when Custom parameters is selected, and is used for time integration.

Enter the Maximum phase fraction change (relative) in a time step

Plot Renderer Settings

Plot Renderer, Plot Renderer: Configuration Settings, and Plot Type: TTT Mode

When setting up your calculation on the Plot Renderer and/or Table Renderer, the following axis variables are available for the conditions defined on the Property Model Calculator.

  • Ferrite molar fraction (OE or PE): The ferrite molar fraction at the end of the transformation, determined from orthoequilibrium (for Ferrite mode “OE” or “OP”) or paraequilibrium (for Ferrite mode “PE”, “NPLE”, or “PP”).
  • Growth Models
  • Parabolic growth rate constant [m/s(1/2)]: The ratio of half-thickness to square root of time. This is calculated from interfacial composition and diffusion coefficients in austenite.
  • Driving force [J/mol]
  • Nucleation rate [1/(m2 s)]: Steady-state nucleation rate of ferrite per unit austenite grain boundary area.
  • Ferrite start, Ferrite half, or Ferrite finish: The times at ferrite fraction being 0.02, 0.50, and 0.98, respectively.
  • Ferrite start (relative), Ferrite half (relative), or Ferrite finish (relative): The times at 2%, 50%, and 98% of the final ferrite fraction, respectively.

Reference

[1988Lan] W. F. Lange, M. Enomoto, H. I. Aaronson, The kinetics of ferrite nucleation at austenite grain boundaries in Fe-C alloys. Metall. Trans. A. 19, 427–440 (1988).