An automated morphological classification of ferrite-martensite dual-phase microstructures

Abstract

In this study, a simple classification scheme based on image processing is proposed to categorize optical microstructures of dual-phase steels with varying morphology (i.e., shape, size and distribution) of ferrite-martensite phases. Dual-phase microstructures with varying morphologies have been developed by employing different heat treatment schedules; namely, intercritical annealing (IA), intermediate quenching (IQ) and step quenching (SQ) using a low carbon micro-alloyed steel. The images of optical microstructures of the developed steels have been first segmented using Otsu thresholding technique and then, the ratio of the black (martensite) and white (ferrite) run-lengths for the phases have been calculated. The mean and median values of these ratios have been considered further, and it has been demonstrated that the mean values are more appropriate than the median values for the classification purpose. The mean and standard deviation of the former parameter for IA, IQ and SQ microstructures are 0.679 ± 0.040, 1.540 ± 0.090 and 0.989 ± 0.119, respectively. The simple classification technique is found to be advantageous from different aspects.