A Novel Approach for Analytical Description of the Isothermal Bainite Transformation in Alloyed Steels

Abstract

Abstract A novel approach for modeling the bainite transformation in alloyed steels during isothermal quenching is presented. The approach is based on the application of the logistic function with the logarithmic argument of the isothermal holding time. The proposed model involves two time-independent fitting parameters, a and b, where are specified for the given isothermal quenching temperature and other conditions (e.g., steel grade, austenite grain size, etc.). The adequacy of the modeling results is estimated using the sum of squared differences between the experimental and calculated bainite fraction formed at every time step Δτ during isothermal quenching. The logistic function was found to provide a fit between the experimental and calculated bainite transformation kinetics that was up to ten times better than that of the conventionally applied Kolmogorov–Johnson–Mehl–Avrami equation. An excellent agreement is achieved between the modeling results and the experimental data for commercially produced high-strength alloyed steels 300M, HY-TUF, and D6AC isothermally quenched in the temperature range of the bainite transformation. The obtained temperature dependences of the model parameters a and b reveal the potential for further theoretical investigation and verification of their physical meaning.