Modification of Grange-Kiefer Approach for Determination of Hardenability in Eutectoid Steel

In this research work, an independent mathematical modeling approach has been adopted for determination of the hardenability of steels. In this model, at first, cooling curves were generated by solving transient heat transfer equation through discretization with pure explicit finite difference scheme coupled with MATLAB-based programming considering variable thermo-physical properties of 1080 steel. Thereafter, a new fundamental approach is proposed for obtaining CCT noses as a function of volume fraction transformed through modification of Grange-Kiefer approach. The cooling curves were solved against 50 pct transformation nose of CCT diagram in order to predict hardening behavior of 1080 steel in terms of hardenability parameters (Grossmann critical diameter, D (C); and ideal critical diameter, D (I)) and the variation of the unhardened core diameter (D (u)) to diameter of steel bar (D) ratio with diameter of the steel bar (D). The experiments were also performed to ascertain actual D (C) value of 1080 steel for still water quenching. The D (C) value obtained by the developed model was found to match the experimental D (C) value with only 3 pct deviation. Therefore, the model developed in the present work can be used for direct determination of D (I), D (C) and D (u) without resorting to any rigorous experimentation.