Thermodynamics in steels at temperatures lower than A1

issues about thermodynamics and their coupling to MICRESS
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nokkikku
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Thermodynamics in steels at temperatures lower than A1

Post by nokkikku » Sat Jul 30, 2011 8:11 pm

Hi there,

I made some gamma-alpha simulation in a steel at 680°C. Its chemical composition is 0.07%C, 1.44%Mn, 0.15%Mo. I put the GES file from ThermoCalc to MICRESS. When I made the GES file, I select the phases fcc, bcc, liq and cementite. Therefore, in principle, the A1 line must appear if there is cementite. Below the A1 temperature, it will be no austenite.

I wonder very much, how MICRESS calculate the composition of the austenite in my simulation at 680°C-under A1 temperature.


Thanks again
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Bernd
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Re: Thermodynamics in steels at temperatures lower than A1

Post by Bernd » Mon Aug 01, 2011 9:47 pm

Hi nokkikku,

Generally, Thermo-Calc gives phase diagrams for equilibrium, so, effects like curvature undercooling, interface kinetics, etc. are not included.
How did you treat cementite in the MICRESS simulation? If you do not explicitly specify cementite to appear or to be present at the beginning, the result will be for the metastable system, as if you would define cementite as "SUSPENDED" in Thermo-Calc.
Can you tell us more about your MICRESS simulation?

Bernd

nokkikku
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Re: Thermodynamics in steels at temperatures lower than A1

Post by nokkikku » Tue Aug 02, 2011 10:47 am

Hallo Bernd,

I didn't take cementite phase into MICRESS calculation. There are just austenite and ferrite. I simulated purely at 680 °C. Min and Max Nucleation temperature = 680°C. Nucleation driving force = undercooling for ferrite seeds at bulk, interface and triple points. Input of phase diagram = database global. Redistribution behaviour = NPLE.

So you meant, although I included cementite in ThermoCalc, but I didn't include it in MICRESS, it would be the same as I 'suspended' it in ThermoCalc, right?

Many thanks

Bernd
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Joined: Mon Jun 23, 2008 9:29 pm

Re: Thermodynamics in steels at temperatures lower than A1

Post by Bernd » Tue Aug 02, 2011 11:23 am

That's it! In MICRESS, only phases which are explicitly defined and nucleated (or set as part of the initial structure) are taken into account. All other phases which you put into the .ges file just make it bigger without having any effect...

Bernd

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