After The Low-alloy Steel Rolling Cooling Process Thermodynamics And Kinetics Of Phase Transformation Model Development

In the process of hot rolling steel, there are some unknown complex function relations among the chemical composition, processing parameters, microstructure and mechanical properties of steel. If people have made sense of those relationships, people could simulate microstructure evolution and predict mechanical properties of the hot rolling process for the purpose of optimizing and controling microstructure evolution, improving material performance by adjusting the chemical compositions and processing parameters. The models for phase transformation thermodynamics and kinetics in the hot rolling process of the steel are very important in the whole microstructure simulation and mechanical properties prediction system, which can calculate the microstructure evolution of the steel in the cooling process after rolling, so as to provide basis for reasonably predicting the final mechanical properties of steel.Based on the physical metallurgy mechanisms, this thesis established ferritic phase transformation thermodynamics and dynamics mathematical models of low alloy steel cooling process after rolling, and tested the CCT curves of the investigated steels through the expansion experiment for verifying the results of calculation. The research works and conclusions of this thesis mainly include:(1) Three different local equilibrium models, Ortho-Equilibrium (OE), Para-Equilibrium (PE) and Negligible/No Partition Local Equilibrium (NPLE), are introduced into the superelement model for the phase transformation thermodynamics calculation. The phase interface concentration, phase transformation driving force and phase transition equilibrium temperature are calculated in the transformation processes of γâ†'α+γ’,γâ†'α+cem for Fe-0.1C-1.5Mn-0.5Si and Fe-0.21C-0.51Mn-0.2Si steels. The Ae3and Ae1calculated under three local equilibrium models are in good agreement with the values calculated by Thermo-Calc and the ones measured in literature, the deviations are less than4%, it proved that the proposed approach is acceptable.(2) Using superelement model and KRC activity model, thermodynamics calculation on two kinds of high strength low alloy experiment steels was impletmented. On the basis of the thermodynamic calculation, the incubation period and the actual start temperature of the phase transformation from austenitic to ferritic, pearlite were predicted using Lange incubation period model and the Scheil additivity rule. The deviations between the measured results and calculated ones satisfy the accuracy requirement.(3) The continuous cooling transformation curves for two high strength low alloy experiment steels were achieved through thermal simulation tests. The calculation results of thermodynamic and kinetic data are in good agreement with the measured results.