Study on kinetics model of bainite transformation under stress
The kinetics of bainite transformation and its modelling have always been a hot research topic.The kinetics model of bainite transformation of a medium-carbon ultrafine-grained bainite steel was studied in detail.Firstly,the kinetics model of bainite transformation proposed by van Bohemen and Sietsma was used to fit the experimental data.It was found that the fitted autocatalytic parameter was less than zero,which did not comply with physical laws.The main reason is that plastic deformation brings about additional nucleation sites,which are preferentially consumed as favorable positions,resulting in a decrease in nucleation rate over time.Based on this mechanism,the van Bohemen and Sietsma models were modified by adding a function g(t)in the original model of bainite nucleation to describe the decrease in nucleation rate.g(t)was defined in two forms:power function and exponential function.Finally,an improved bainite transformation kinetics model was obtained.The autocatalytic parameter obtained by fitting the improved model is greater than zero,which conforms to physical laws.In addition,when g(t)is a power function,the calculation accuracy is higher and the model form is more concise.
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