Chemical banding revealed by chemical etching in a cold-rolled metastable stainless steel

• Published in: Materials characterization Vol. 84; pp. 142 - 152
• Main Authors: Celada, C., Toda-Caraballo, I., Kim, B., San Martín, D.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.10.2013; Elsevier
• Subjects: Applied sciences; Austenitic stainless steel; AUSTENITIC STEELS; Chemical banding; COLOR; Color etching; Cross-disciplinary physics: materials science; rheology; ELECTRON MICROPROBE ANALYSIS; EPMA measurements; ETCHING; Exact sciences and technology; FERRITE; Forming; MATERIALS SCIENCE; Metals. Metallurgy; MICROSTRUCTURE; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; PRECIPITATION HARDENING; Production techniques; Rolling; SEGREGATION; Solidification; STAINLESS STEELS; Austenitic stainless steel; Chemical banding; Segregation; Color etching; EPMA measurements; Cold rolling; Forming processes; Austenitic steels; Cold rolled sheet; Chemical etching; Microstructure; Stainless steels
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2013.07.018

The current work describes the metallographic characterization of the initial microstructure of a cold rolled precipitation hardening semi-austenitic stainless steel (12Cr–9Ni–4Mo–2Cu–1Ti, in wt.%). The use of the Lichtenegger and Blöch (L–B) color etching solution has been shown to reveal not only the phases present in the microstructure, but also the existence of chemical banding along the rolling direction. The L–B reagent has been found to color the microstructure in bands depending on what alloying elements have segregated to each band. Two-dimensional electron probe microanalysis (EPMA) maps have shown that Ni, Cu and Ti segregate together in the bands, while Cr has an opposite behavior. Mo has a mixed segregation behavior although much weaker than the other elements and more prompt to segregate like Ni does. A direct comparison of light optical micrographs with the EPMA maps of the same area of the microstructure has enable to establish a direct relationship between the alloying element band concentration and the resulting etching color contrast obtained with the L–B reagent. Thermodynamic calculations predict that solidification in this steel takes place with ferrite as the primary phase. Equilibrium partitioning coefficient calculations seem to support the observed segregation patterns. •A cold rolled metastable stainless steel has been characterized thoroughly.•EPMA shows that Ni, Cu and Ti segregate together; Cr in an opposite way.•L–B color etching is sensitive to the segregation of these chemical elements.•This chemical banding has been reduced by applying a homogenization heat treatment.•Partitioning coefficient calculations agree with the observed segregation patterns.