Dual phase steel etchants-Chemical etching

Material: Dual phase steel etchants
Type: Micro
Method: Chemical etching
Etchant (electrolyte): 1.) Lawson et al. used: Solution a: 4 g picric acid in 100 ml methanol, Solution b: 8 g CrO3, 40 g NaOH in 72 ml water. Etch with a first, then b boiling. Martensite is black, "old ferrite" is gray, "new ferrite" is white. 2.) Rigsbee and Vander Arend used: 2 g ammonium persulfate, 2 ml HF, 50 ml acetic acid, 150 ml water. Martensite is darkened, retained austenite is lighter than ferrite. 3.) Arnie Marder and Arlan Benscoter used: Solution a: 2 ml nitric acid in 98 ml ethanol Solution b: 10 g sodium metabisulfite in 100 ml water Pre-etch with a 1-2 s, then immerse in b at RT for about 20 s. Martensite is dark, ferrite is off white, austenite is white.
Procedure: Please see the upper text.
Note: Duplex Stainless steels with ferrite and austenite.
Source: http://www.metallography.com.

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