Kinetic modeling of non-equilibrium grain boundary segregation behaviour of Nb during welding thermal cycle
The welding thermal cycles of HSLA steels with three different Nb contents(0.180%,0.085%,0.025%)were simu-lated using the Gleeble-3500 thermal simulator under varying cooling rates.The non-equilibrium grain boundary segregation behavior of Nb atoms was characterized by electron probe microanalysis(EPMA),and the Nb atom segregation at grain boundaries was quantified under different Nb contents and cooling rates.Based on the non-equilibrium grain boundary segre-gation kinetics,the vacancy formation energy was determined to be 1.403 eV.Additionally,the critical time constants for non-equilibrium segregation of Nb atoms in steels with 0.180%and 0.085%Nb content were calculated as 7.59×103 and 6.0×103,respectively.Furthermore,by treating the diffusion coefficient of Nb atom-vacancy complexes as a variable,the relation-ship between the diffusion coefficient and the equivalent time was calculated and revised,leading to the establishment of a cor-rected kinetic equation for non-equilibrium segregation of Nb atoms under welding thermal cycles.
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维普
