STUDY ON THE GRAIN REFINEMENT OF ATIBEARING INTERSTITIAL FREE (LF) STEEL DURING WARM DEFORMATION

Warm deformation was applied to an IF steel using warm torsion and ARB process at 500C. The maximum equivalent strain for both methods was 4.8 which were applied to ARB sample in 6 cycles. The microstructure evolution and grain refinement were studied using scanning electron microscopy equipped with Electron Back Scattered Diffraction (EBSD). Microstructure evolution is similar in both methods and the grains were elongated and become parallel in deformation direction and divided to sub-grains during deformation. The grains refine and misorientation angle increases with increasing strain gradually, but the this trend is stronger in ARB samples and they have finer grains and higher misorientation angle in compare to warm torsion due to higher strain rate and stored energy. At the large strains most of the grain boundaries are high angle boundaries (misorientation > 15) and the ultra fine grains (<1 um) appear in the microstructure. The Zener-hollomon parameter has a power law relationship with the grain size in deformation and normal to deformation directions. The grain size in ARB process can be predicted ifwarm torsion performed at the same conditions.

Keywords:

Warm Deformation , Grain Refinement , ARB , Torsion , EBSD , Ultra Fine grains