*3.4. Characterization Methods*

Samples from the as-received heats, grain coarsening studies and hot compression studies were analyzed using optical microscopy Nikon FX-35WA (Nikon Corp., Tokyo, Japan). Standard metallographic techniques were employed by mounting in Bakelite, grinding samples using waterproof abrasive silicon carbide papers gradually from grit 180 to 600 and polishing using alumina powders of 1 and 0.05 μm. The prior austenite grain boundaries were revealed using a special reagent consisting of 100 mL of saturated aqueous picric acid with the addition of 1 mL hydrochloric acid (HCL) and 10 g of sodium dodecylbenzene sulfonate as a wetting agent at 70 ◦C. The mean austenite grain sizes were measured using ImageJ (1.52a, National Institutes of Health, Bethesda, MD, USA), by manually outlining the austenite grains and calculating the equivalent grain diameter for each grain. From each sample, at least 400–500 grains were measured. Additionally, selected as-received samples were characterized using Vickers hardness tester LECO LM310AT (LECO Corp., St. Joseph, MI, USA). At least 5 Vickers hardness measurements with a load of 300 Kgf were taken from each direction in each of the selected samples. Further, in this study, EBSD Mapping was done in FEI Scios FIB/SEM Dual Beam (Thermo Fisher, Hillsboro, OR, USA) equipped with EDAX EBSD camera and TEAM software (V4.3, EDAX Inc., Mahwah, NJ, USA). Thin foils were examined under transmission electron microscope (TEM) using JEOL JEM2100F operating at an accelerated voltage of 200 kV.
