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T. Wojcik, E. Kozeschnik:
"Thermo-kinetic simulation of TTP-diagrams for NbC precipitation in austenite";
Talk: MS&T 2013, Montreal, Kanada; 2013-10-27 - 2013-10-31.

Hot deformation of Nb-bearing microalloyed steel accelerates the precipitation of NbC. The strain-induced increase of the dislocation density provides additional heterogeneous nucleation sites for precipitation and speeds up the diffusion significantly. Dutta and Sellars [Mat. Sci. and Tech., 3(1987)] have introduced a semi-phenomenological model to describe the onset time of precipitation, which was presented in time-temperature-precipitation (TTP) diagrams. The aim of the present work is the simulation of NbC precipitation in HSLA steel based on classical nucleation theory and using CALPHAD-assessed thermodynamic and diffusion mobility databases. Several important input quantities of the simulation, such as the effective volumetric misfit or diffuse interface corrections to the interfacial energy of NbC precipitates in austenite, were either taken from independent experiments or determined by calibration with available experimental results. The dislocation density evolution is accounted for with a newly developed model. The simulation results compare well with experimental data of deformed and undeformed austenite.

precipitation, microalloyed steel, thermo-kinetic simulations, TTP