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T. Wojcik, E. Kozeschnik:
"Shell-wise growth of (Nb,Ti)(C,N) precipitates during cyclic cooling of microalloyed steel";
Talk: EUROMAT 2013, Sevilla; 2013-09-08 - 2013-09-13.

Nucleation and growth of almost stoichiometric NbC- and TiN-precipitates, as well as complex carbonitrides in microalloyed steel is well investigated. Due to different solubility products TiN nucleates at higher temperatures than NbC in austenite. Both phases have the same fcc crystal structure with very similar lattice constants and are able to form complex Nb-Ti-carbonitrides. The composition of these precipitates depends on the temperature and chemistry of the matrix.
In the present work a cooling profile from 1200°C to 800°C is introduced. It consists of 9 cycles with temperature oscillations of over 100°C. A TEM-investigation of samples treated in this way shows many populations of precipitates. The larger ones show a zonal growth structure of shells with local Nb- and Ti-enrichment. The experimental setup is modelled by the thermo-kinetic software MatCalc, which allows the simulation evolution of precipitates in various multi-component multi-phase alloy systems. The calculated results are in a good agreement with the experimental data.

precipitation, TEM, microalloyed