*2.3. Optical, Scanning Electron Microscopy and EDS—EBSD Analysis*

The microstructural characterization of the samples in the starting and after heat treated were prepared for optical (OM), scanning electron microscopy (SEM) and EDS analysis by using standard metallographic procedures. Specimens for EBSD analysis were subjected to standard sample preparation followed by vibro-polishing in a VibroMet® polisher (Pace Technologies, Tucson, AZ, USA) for 3 h with 0.05 μm nanometer alumina suspension.

The SEM analysis was conducted on a ZEISS Sigma 500 VP scanning electron microscope (ZEISS, Pittsburgh, PA, USA) equipped with Oxford Aztec X-EDS (Oxford Instruments, Abingdon, UK) with an operating voltage between 10 kV and 20 kV. Electron Backscattered Diffraction (EBSD) and Image Quality (IQ) analyses were conducted on a FEI Scios FEG scanning electron microscope (University of Pittsburgh, Pittsburgh, PA, USA) equipped with an EBSD system. An accelerating voltage of 20kV with a beam current of 13 nA were used. The details of dwelling time, tilt angle, distance, scanned area and step size and the details for the EBSD-IQ phase-microstructural analysis are also described elsewhere [10]. The EBSD-IQ approach was used to measure the volume fraction of the microconstituents formed during intercritical and supercritical annealing treatments. An area of 100 μm × 100 μm with a step size of 0.2 μm was employed.
