A New Approach for Color Metallography: Through Controlled Conditions to Objective Microstructure Analysis of Low-Carbon Steels by LePera-Etching

Abstract

Although metallography is a very old discipline, its importance is growing steadily. High-performance materials need an accurate evaluation of the microstructure to guarantee the ever-tightening specifications in the range of properties and to control the production process. With the continuously growing demand of well-tailored microstructures, in most cases with smaller and more complex constituents of defined geometry, the requirements for reproducible metallography are also more and more challenging. In this contribution, we want to show how new trends in metallography can help scientists and engineers ensure reproducibility in their daily work with etching routines governed by controlled and monitored systems. The presented setup keeps all critical parameters during color-etching constant. Thus the reproducibility and homogeneity of LePera etching on low-alloyed steel can be guaranteed. Furthermore, a parameter study for LePera was conducted not only to show the application range of critical parameters such as temperature and time but also to find the best parameter setting for an automated phase-separation toward image analysis and microstructural classification. With the help of a focused ion beam, quantitative correlations of the etching mechanism can also be derived.

Overview: Machine Learning for Segmentation and Classification of Complex Steel Microstructures

“…The combination of picric acid-based etching with DL segmentation allows for quantification of PAGS with unprecedented quality and robustness. Although established as a standard etchant for PAG analysis, picric acid-based etching still represents an additional effort compared to other steel etchants or is no longer used at all in some laboratories due to safety concerns [95]. Therefore, Bachmann et al [46] investigated in a case study to what accuracy the PAGS can be determined with a simple Nital etching.…”

Investigating the Kinetics of Layer Development During the Color Etching of Low-Carbon Steel with In-Situ Spectroscopic Ellipsometry

“…Penetration depth defines the measure of how deep a certain light component can penetrate a medium and is calculated as in Eq. (7).…”

“…Although the range of applications is relatively wide for different etchants, there have been only a few efforts to understand the kinetics of the etching process, especially for color etchants. In some cases, the chemical reactions were (at least partly) revealed, but etchants are used primarily out of habit without a proper understanding of the kinetics of the ongoing chemical reaction [7,8]. In addition, these studies focused specifically on the kinetics of etching of organic compounds or semiconductor materials but never on metallographically inspected alloys [9,10].…”