The inadequacy of the geometric features of MA islands in relating bainite microstructures to composition and processing conditions

TL;DR

This study investigates whether geometric features of MA islands in bainite steels can reflect processing conditions, finding that these features are largely invariant and thus inadequate for such analysis.

Contribution

It provides a comprehensive statistical analysis of MA island geometries across various bainite steels, highlighting their limited correlation with processing parameters.

Findings

Geometric features show minor variation across different conditions.

Distribution of MA island forms is nearly identical regardless of composition.

Geometric features are inadequate for relating microstructure to processing conditions.

Abstract

Achieving desired properties in bainite steels with MA islands demands understanding the affect of processing conditions and composition on their size and morphology. Generally, this understanding is gained by studying the change in the size and morphology of the MA islands with composition and the processing conditions. In the present work, around 8500 MA islands dispersed across of approximately 1500 bainite microstructures are investigated to comprehend the influence of composition and heat treatment cycle on the geometric features. The geometric features considered in this study include polygon area metric, compactness and aspect ratio. A thorough statistical analysis of these features across bainite steels of different compositions and processing conditions unravel that, though there are minor changes, no characteristic variation is introduced in the size and morphology of the MA islands. In other words, the distribution of the various forms of MA islands are almost identical in bainite steels of different chemistry and heat treatment, thereby indicating the inadequacy of geometric features in explicating the affect of processing conditions on microstructure.