pearlite to austenite transformation

solid-solid phase transformations, influence of stresses and strains
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vmattosferreir
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pearlite to austenite transformation

Post by vmattosferreir » Wed Feb 16, 2022 1:28 pm

Hello,

I've been trying to simulate the austenite formation from an initial pearlitic structure.
For the initial microstructure, I do consider the cementite lamellae. For my last simulations, I set the initial concentrations of each phase based on APT measurements instead of the equilibrium concentrations obtained via Thermo-Calc.
However, if I check the ".log" file I observed the following message which I can't understand.
Could you please help me with this issue? I am not sure how it can affect the simulation since I am unable to check the initial concentrations in each phase.

Thank you in advance.

Kind regards,
Vitoria.
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Bernd
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Re: pearlite to austenite transformation

Post by Bernd » Wed Feb 16, 2022 2:51 pm

Dear Vitoria,

Based on what you marked by color in the screen output you show, there are two issues you raise:

The first one is that slopes cannot be calculated for Mn and C in cementite. This is in first place because you (as it seems) defined them both manually as stoichiometric. As you can see from the "Start Compositions and Limits for Quasi-Equilibrium calculation" output at the top, there is indeed no solubility range for C in cementite, so that it would automatically be defined by MICRESS as stoichiometric anyway. But Mn has a broad solubility range, and you would not need to set it stoichiometric (but you can).
The fact that there is no solubility range of C in cementite (as modeled in the database) means that you should not use an initial composition for this element in cementite other than 25 at%. Unfortunately, it is quite difficult to input exactly this value in wt% because it also depends on the Mn composition. Why don't you choose the equilibrium value as initial value? If you think the initial compositions should correspond to the equilibrium at another temperature, you still can do that by choosing the corresponding "temperature for initial equilibrium".

The second issue is the warning about reading the initial microstructure from file as 2 grains. MICRESS here just reminds you that if the two grain numbers should rather be interpreted as phase numbers, you should use the phase_to_grain switch.

Bernd

vmattosferreir
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Re: pearlite to austenite transformation

Post by vmattosferreir » Tue May 03, 2022 10:19 am

Dear Bernd,

thank you for your reply.
If I set the initial composition to be the same as the equilibrium the simulation works fine. However, I would like to use the values obtained from APT.
My question is: is that currently not possible in MICRESS?

Kind regards,
Vitoria.

Bernd
Posts: 1504
Joined: Mon Jun 23, 2008 9:29 pm

Re: pearlite to austenite transformation

Post by Bernd » Tue May 03, 2022 4:25 pm

Dear Vitoria,

This is not a question whether it is possible in MICRESS, but whether the thermodynamic database supports that. In the phase model of cementite in the database, C is occupying an own exclusive sublattice, so that the composition of C cannot be different from 25 at%! Even forcing a different value would not succeed.
However, you can chose the Mn composition according to the APT measurement without problems. Just take care that the carbon composition in wt% corresponds to exactly 25 at% for this given Mn-content (or generally switch input to at%).

Bernd

vmattosferreir
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Re: pearlite to austenite transformation

Post by vmattosferreir » Tue May 10, 2022 2:31 pm

Dear Bernd,

thank you for your reply.
We actually tried using the exact 25at% value in cementite but we still have the same error.
I will send you the files in a private message.

Kind regards,
Vitoria.

Bernd
Posts: 1504
Joined: Mon Jun 23, 2008 9:29 pm

Re: pearlite to austenite transformation

Post by Bernd » Wed May 11, 2022 3:44 pm

Dear Vitoria,

I cannot see any error in the .log file. What is going wrong? You should also send the .dri and .scr-files so that I can see.

You are reading initial compositions and initial microstructure from file. If these data comes from experiments, it is quite probable that you have local inconsistencies which could cause problems. It is also not trivial to do the correction to x(C)=0.25 in this case.

Further, you should not define Mn as stoichiometric within cementite, if you define a phase interaction (fcc/cementite) with "paratq".

Bernd

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