Microstructural manifestations in color: Some applications for steels

The interpretational advantages of colored microstructures over conventional black-and-white images is recognized in view of the natural response of the human eye to color variations. This applies well for steels, where ambiguities in phase and feature discrimination can often arise from intrinsic lack of contrast or otherwise subtle grey-level differences of the observed microstructural constituents. Although staining techniques are advantageous from this standpoint, their use, even today, is rather limited in routine metallography. Textbook instructions and standard reagent formulations alone cannot guarantee optimum results unless sample preparation is meticulous and the etching technique is perfected. Moreover, the etch response of different steel chemistries being unique to each grade demands experimentation as a prerequisite for obtaining optimum results. This article provides a pictorial insight into the fascinating world of microstructures obtained in a gamut of plaincarbon, dual-phase, low-alloy, stainless, and high-alloy tool steels investigated in our laboratory. Issues concerning the revelation of anodic matrix and second phases and crystallographic orientation aspects of microstructural features, such as grains, twins, and colonies, are also elucidated and discussed.