Modeling of grain growth kinetics in complexly alloyed austenite

Abstract

A quantitative model is presented to describe the kinetics of grain growth in complexly alloyed austenite. The model assumes that the activation energy of grain growth is proportional to the activation energy of bulk self-diffusion, which is calculated as a function of the chemical composition of the solid solution using the previously obtained formula. The empirical parameters of the model are determined on the basis of experimental data on the kinetics of isothermal grain growth in steels with the chemical composition varying in a wide range: C (0.05 ÷ 0.32), Mn (0.30 ÷1.88), Si (0.01÷ 0.29), Ni (0.0 ÷ 4.0), Cr (0.0 ÷ 2.0), Mo (0.0 ÷ 0.5), Nb (0.00 ÷ 0.05) available in the literature. The model allows one to obtain good agreement with the experiment for the considered steels in which the minimum (~ 79.7 kJ / mol) and maximum (~ 243.7 kJ / mol) values of the activation energy of grain growth differ by 3 times. The average absolute value of the relative error in calculating the grain size is about 11 % that is comparable to the measurement error. Taking into account the influence of the chemical composition on the activation energy of grain growth, implemented in the developed model, it is possible to obtain agreement with the experiment without accounting for the solid-solution pinning of moving boundaries (the solute drag effect) requires a large number of additional empirical parameters (two exponential parameters for each alloying element). This result deserves further consideration from the physical viewpoint and verification on both simple carbon steels and steels with various quantities of Mn, Mo and Nb, which, according to literature, exert the strongest solute drag effect.

MODELING of static recrystallization IN alloyed austenite with account of recovery

“…With allowance for the physically motivated correlation between AESD and the activation energy of recrystallization, we will presume proportionality of these parameters where the former depends on chemical composition of steel [7]. This presumption has been previously verified [8] by successful modeling of the normal grain growth in austenite of complexly alloyed steels.…”

Integral Computer Model for Simulating Microstructure Evolution during Thermomechanical Processing and Heat Treatment of Steels and Predicting their Final Mechanical Properties

“…Grain growth model. This model [8] assumes proportionality of the grain growth activation energy to the activation energy of bulk self-diffusion dependent on chemical composition of solid solution in accordance with a previously obtained formula [9]. Empirical parameters are determined on the basis of experimental data available in literature on kinetics of isothermal grain growth for 10 steels in a wide range of chemical composition: C(0.05÷0.32), Mn(0.30÷1.88), Si(0.01÷0.29), Ni(0.0÷4.0), Cr(0.0÷2.0), Mo(0.0÷0.5), Nb(0.00÷0.05).…”

“…Our approach to the ferritic transformation differs from existing analogues by the novel formulation of complex alloying effect on the nucleation rate of ferrite grains and mobility of α/γ−boundaries. Moreover, the model takes into account the effect of alloying by substitutional elements on the carbon diffusion coefficient of in bulk austenite [15]. The bainitic transformation model is briefly described in [4].…”