Multiple etchings methodology: A new approach in multiphase steel characterization.

Following the first and second generation, the challenge in obtaining a better balance between strength and elongation is still the main characteristic of the third generation of Advanced High Strength Steels (AHSS). With this, the use of multiphase microstructures has increased over the last few years. It can be difficult to characterize all the phases with only Optical Microscopy (OM), so the use of Scanning Electron Microscopy (SEM) is essential for accuracy in cases where researchers lack experience. In order to expand the possibilities, this research proposed a new approach that would allow experienced researchers to characterize multiphase steels using only OM. A high silicon steel was austempered slightly below Ms temperature for three different time periods in order to obtain different quantities of martensite, bainite and retained austenite. X-Ray Diffraction (XRD) was carried out in order to confirm and obtain retained austenite volume fractions, and the results indicated that shorter holding times were not enough to enrich and stabilize retained austenite. Then, each samples was etched with four different etchants. Results showed that the new Multiple Etchings Methodology (MEM) allowed a better visualization of all the phases when viewed together. Beraha Martensitc revealed non-tempered martensitic microstructures. Sodium Metabisulfite revealed retained austenite. LePera and Nital were the best at revealing the evolution of the microstructure over time, even with the changes which occurred due to martensite tempering. SEM images confirmed the results obtained via MEM.im This article is protected by copyright. All rights reserved.