pearlite transformation

Discussion of numerical issues which are not directly linked to specific applications
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shaojielv
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pearlite transformation

Post by shaojielv » Thu Mar 17, 2022 7:35 am

Hi, everyone
I have the following questions about pearlite transformation and hope to get your help.
Firstly, I simulated pearlite transformation through coupling case T018 and Thermocalc, but the result was different from what we expected. I don't know whether the result is correct. The simulation result is as follows and attached.I hope to get your opinion.
Second, I want to simulate the austenite to pearlite transformation, and will represent the ferrite + pearlite piece of lamellar cementite, but I didn't think it should be how to set up and the location of the point of nucleation, through literature, I understand the mechanism of this kind of layered structure, as shown in figure simulation for the references of lamellar pearlite, but I don't know what should to establish model.
Finally, I would like to express my thanks and wish you a pleasant life. Work well.
Attachments
problem 2.png
problem 2.png (21.57 KiB) Viewed 3192 times
T018_GammaAlphaPearlite_TQ.dri
(29.3 KiB) Downloaded 100 times
pearlite.png
pearlite.png (20.18 KiB) Viewed 3192 times

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

Re: pearlite transformation

Post by Bernd » Thu Mar 17, 2022 11:48 am

Dear shaojielv,

Generally, when setting up a simulation of pearlite formation, one has to decide on the lenth-scale: Is the aim to get the spatially resolved eutectoid morphology of the pearlite, i.e. the cementite and ferrite lamellae, or is it sufficient to model pearlite in an "unresolved" or diffuse manner in a bigger scale, where you also can see the ferrite grains. Example T018 does the second, so that only a phase mixture of cementite and ferrite is the result (indicated by a chess-pattern in the .phas output). In which sense does this not match your expectations?

If you want to go for a resolved structure like the one you showed in the attached images, you typically perform a directional simulation with few grains of cementite and ferrite at the bottom, applying a constant cooling rate and temperature gradient, and starting from the eutectoid temperature. Unfortunately, we currently don't have an application example for resolved pearlite.

Bernd

shaojielv
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Re: pearlite transformation

Post by shaojielv » Thu Mar 17, 2022 3:51 pm

Dear,Bernd
Yes, there are currently no examples of this in Micress, so I hope I can implement such a process myself. I see what you mean, but I still have some questions to ask you.
First, because in the literature emerged as a result, so I think MICRESS is certainly can realize such a process, the formation for the above mentioned pearlite can I understood as such: we will be the whole simulation domain as austenitic, and make the ferrite and cementite in the bottom of the simulation domain nucleation, the directional growth? If so, can we nucleate ferrite on austenite without cementite, and then nucleate cementite grains on ferrite? Should our nucleation temperature be set to the eutectoid point temperature? Or is there anything else I should pay attention to?
Second, in addition to the directional growth of lamellar pearlite mentioned above, what is the difference between lamellar pearlite and orientation in polycrystalline austenite grains? As the following example, sincerely thank you.
lv
Attachments
zhuguangti.png
zhuguangti.png (432.64 KiB) Viewed 3188 times

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

Re: pearlite transformation

Post by Bernd » Thu Mar 17, 2022 4:51 pm

Dear shaojielv,

I am not an expert on pearlite, so I don't really know what determines the direction of the lamellar growth if there is no temperature gradient. It may be anisotropy, misorientation, or concentration gradients. However, there is always a temperature gradient if there is cooling!

In principle, you could make the simulation like in your attached graphics, starting from pure austenite. However, please keep in mind that the length-scales between lamellae and grains are probably very far.

In MICRESS, you do not need to know the nucleation temperature (although it is helpful for narrowing the temperature range). What you need to specify instead is a critical undercooling. However, I would advice you to begin with already existing cementite and ferrite lamellae in your first trials, because eutectic growth is quite tricky and unstable, and it becomes even more difficult if you start with nucleation...

Bernd

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