Modeling of Austenite Decomposition during Continuous Cooling Process in Heat Treatment of Hypoeutectoid Steel with Cellular Automaton Method

Abstract

The austenite decomposition during continuous cooling process in heat treatment of hypoeutectoid steel is studied with experimental method and numerical simulation. To investigate the phase transformation, quenching experiments are conducted and the microstructure evolution is investigated through metallographic examination. Dilatometric experiments are conducted as well and the experimental results are employed to analyze the phase transformation process during austenite decomposition. Subsequent studies of austenite decomposition in the steel are conducted using a numerical model based on cellular automaton (CA) method. In the simulation, the transformation of austenite into ferrite and pearlite is simulated, and the growth kinetics and average grain size of ferrite as well as the average interlamellar spacing of pearlite were obtained. The simulation results of the effects of cooling rate on the average grain size of ferrite and interlamellar spacing of pearlite agree well with the experimental results. Finally, integrated with a previously developed model for the austenization in heating process of heat treatment, the present model shows a capacity to investigate the effect of the prior austenite grain size on the final microstructure formed at the end of austenite decomposition.

Multi-Scale Modeling of Microstructure Evolution during Multi-Pass Hot-Rolling and Cooling Process

“…For the γ→α phase transformation in Fe-C-Mn alloys, the growth kinetics have been usually described by carbon diffusion and interface reaction based on the paraequilibrium condition, where only the interstitials are allowed to partition and reach the equality of chemical potentials between the α- and γ-phases, while the substitutional elements are not [ 34 ]. Several numerical simulation studies focused on the α-γ phase transformation during isothermal annealing [ 23 , 24 ], continuous cooling [ 25 , 26 ], continuous heating [ 27 , 28 ], and an entire anneal cycle [ 29 , 30 , 31 ] under the assumption of paraequilibrium. To account for the interaction of substitutional elements at the moving α/γ interface, Purdy et al [ 35 ] proposed a solute drag model, where the Gibbs energy dissipation due to the trans-interface diffusion of the substitutional solute was introduced.…”

“…As a result of inherent experimental difficulties, these studies cannot fully elucidate the physical mechanisms contributing to grain refinement, because one needs to consider the temporal evolution of the multi-pass processes of recrystallization and the γ→α transformation, With the development of technologies in computer science, numerical simulation methods have popularized and become an important tool for understanding the mechanisms of microstructure formation during material processes due to their capabilities to present the visual, temporal evolution of microstructures. Among different numerical models, the cellular automata (CA) approach, combining both computational efficiency and simplicity [8], has been commonly applied to investigate various phenomena such as recrystallization [9][10][11][12][13][14][15][16][17][18][19][20][21][22], phase transformation [23][24][25][26][27][28][29][30][31], and grain coarsening [32,33].…”

Influence of Graphite Nodules on the Microstructure and Mechanical Properties of Hollow Ductile Iron Pipe after Austempering Treatment

“…According to the Fe–C equilibrium phase diagram, the liquid was transformed to austenite and spheroidal graphite through a eutectic reaction, and then the austenite was decomposed to ferrite or pearlite in the following solidification. Both the graphite nodules and the cooling rate would have affected the phase constituents in the as‐cast ductile iron, in which the pearlite fraction decreased with the increase in graphite nodules but increased with the increase in cooling rate . Therefore, it could be inferred that cooling rate played the predominant role for ductile iron in the present study because the S‐550 sample with a fast cooling rate contained more pearlite.…”

The combined effect of chemical composition and cooling rate on transformation temperatures of hypoeutectoid steels

“…The model considers the effects of phase transformations latent heat, initial austenite grain size, deformation hardening of austenite, etc. Su, Ma and Han [20] simulated the decomposition of austenite into ferrite and pearlite during the continuous cooling of the hypoeutectoid steel with the cellular automaton method.…”