P_13: Paraequilibrium Precipitation of Cementite Fe-C-Cr
In this example, the precipitation of cementite during tempering of a Fe-Cr-C steel is simulated considering two interface conditions: one is the usual ortho-equilibrium condition; the other is the para-equilibrium condition. The simulation results are compared with the experimental data from Sakuma et al. [1980Sak].
This example demonstrates that the early stage of the cementite precipitation can only be accounted for by a simulation applying the para-equilibrium condition, under which the precipitation kinetics are controlled by the diffusion of C. The comparison also shows a later stage gradual transition from the para-equilibrium condition to the ortho-equilibrium condition, and if the tempering time is long enough the diffusion of Cr has a dominating effect on the coarsening of cementite.
For more background information, see the theory described in Growth.
Example Settings
System (System Definer) | |
Database package | Demo: Steels and Fe-alloys (FEDEMO, MFEDEMO) |
Elements | Fe, Cr, C |
Conditions (Precipitation Calculator) | |
Composition |
Fe-0.95Cr-1.065C Mass percent |
Matrix phase |
BCC_A2 All other defaults are kept. |
Precipitate phase |
CEMENTITE_D011 Click Show Details to select the Growth rate model (Simplified (OE) and Para-eq) (PE). All other defaults are kept. |
Calculation Type (Precipitation Calculator) | |
Calculation type | Isothermal |
Temperature | 773 Kelvin |
Simulation time |
20 hours for the paraequilibrium model and 600 hours for the simplified model. |
Datasets (Experimental File Reader) | |
1980 Sakuma | Data set included with this example and imported to one Experimental File Reader. |
Visualizations
Many of our Graphical Mode examples have video tutorials, which you can access in a variety of ways. When in Thermo‑Calc, from the menu select Help → Video Tutorials, or from the main My Project window, click Video Tutorials. Alternately, you can go to the website or our YouTube channel.
Open the example project file to review the node setup on the Project window and the associated settings on the Configuration window for each node. For some types of projects, you can also adjust settings on the Plot Renderer Configuration window to preview results before performing the simulation. Click Perform Tree to generate plots and tables to see the results on the Visualizations window.
When you run (Perform) this example, it can take over two hours to complete the calculations.
There is a variety of information shown in the Visualizations window that can be viewed during configuration and after performing the calculation.
- Thermal Profile: When setting up a calculator on a Configuration window for Isothermal or Non-isothermal Calculation Types, you can preview the profile and adjust settings as needed. When you click a calculator node in the Project window, the matching name of the node is on the tab(s) displayed in the Visualizations window.
For TTT Diagram and CCT Diagram calculations there is nothing shown for the Precipitation Calculator tab in the Visualizations window as there is no Thermal Profile to be defined.
- Plot or Table results: After completing the set up and performing the calculation, to view the matching name of the node on tab(s) in the Visualizations window, either click a Plot Renderer or Table Renderer node in the Project window or click the tabs individually in the Visualizations window.
For this Isothermal example, its Thermal Profile is also displayed in the Visualizations window showing the constant temperature entered for this calculation type. The tab names match the node names in the Project window.
Figure 1: These results compare the predicted and measured evolution of the mean radius of cementite with the experimental data from [1980Sak] to simulation predictions obtained from the ortho-equilibrium (OE), and para-equilibrium (PE) approximations of the precipitate composition. The precipitate growth kinetics exhibited by cementite can be rationalized by the transition from PE to OE.
Reference
[1980Sak] T. Sakuma, N. Watanabe, T. Nishizawa, The Effect of Alloying Element on the Coarsening Behavior of Cementite Particles in Ferrite. Trans. Japan Inst. Met. 21, 159–168 (1980).