Color Light Metallography Versus Electron Microscopy for Detecting and Estimating Various Phases in a High-Strength Multiphase Steel

In this study, fresh attempts have been made to identify and estimate the phase constituents of a high-silicon, medium carbon multiphase steel (DIN 1.5025 grade) subjected austenitization at 900 °C for 5 min, followed by quenching low-temperature bainitizing (Q&B) 350 200 s. Several techniques were employed using different chemical etching reagents either individually (single-step) or in combination two more etchants succession (multiple-step) conducting color metallography. The results showed that complex microstructures comprising fine mixture bainite, martensite retained austenite selectivity stained/tinted with good contrasting resolution, as observed via conventional light optical microscopy observations. While carbon-enriched martensite-retained (M/RA) islands revealed cream-colored areas double-step technique 10% ammonium persulfate Marble’s reagent, dark gray-colored bainite packets easily distinguishable from brown-colored regions. However, high-carbon M/RA could be differentiated only after resorting triple-step 2% nital, solution then warm reagent 30 °C. This orange-colored contrast constituents, besides presence laths bainitic matrix. A quadruple-step involving successive solution, finally Klemm’s Ι 40 even better comparison technique, particularly distinguishing RA martensite. Observations advanced like field emission scanning electron (FE-SEM) back scatter diffraction (EBSD) failed differentiate untempered, matrix, respectively. Transmission (TEM) studies successfully distinguished martensite, noticed islands. volume fraction estimated EBSD, XRD point counting method on micrographs etched samples agreement.