| Microstructural modelling for prediction of the grain size of steels were reviewed and the approaches to obtain a fine grain structure were discussed based on the underlying physical metallurgy and the availability of various process control parameters. The control parameters which determine the ferrite grain size are the initial austenite grain diameter, the amount of retained deformation, the type of the nucleation site, the cooling rate and the transformation temperature. The ferrite grain size can be expressed in terms of the nucleation and the growth rates, but an exact evaluation of it seems to be difficult due to uncertainties involved in determining various physical factors, such as surface energy, diffusivity etc. Therefore, various regression equations are used for the grain size prediction. Large deformation and rapid cooling appears to be effective for grain refining. Attempts are made to estimate the obtainable grain size under a given processing condition. In addition, the effectiveness of the magnetic force are also discussed. |
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