Dynamic Recrystallization and Grain Refinement of Fe-P-C-Si and Fe-P-C-Si-N Steels

Grain refinement is an effective technique to improve the mechanical properties of steels. In the present work, single-pass hot compression experiments have been conducted on two different compositions of high phosphorous steels to study the microstructural evolution and ferrite grain refinement at various strain rates and deformation temperatures, i.e., 0.01-10 s⁻¹ and 750-1050 °C, respectively. Optical metallography has been employed to understand the physical processes that take place during hot deformation process. The results indicate that when these compositions of high phosphorous steels are worked at relatively low temperatures in the intercritical regions, a ferrite grain size of 5-7 µm is obtained. It is observed that the grain size decreases with an increase in strain rate and with the decrease in deformation temperature. Based on the values of stress exponent (n) obtained in the present work, dislocation creep is identified as the deformation mechanism. The activation energies for deformation of these two types of high phosphorous steels have been calculated. The effect of the alloying elements on the stress–strain curve, microstructure, and grain refinement has been discussed.