Etching process.
how to eliminate dark spots in the microstructure.I etched with glyceregia and acetic acid mixed with HCL and nitric acid.
Dear Preetish,
you could have put a photo graph of the micro structure, the problem is not defined fully. What do you want to visualize in the micrstructure , pl go thru the link attached, I think it will bring more clarity.
Dear Preetish,
For this steel grade I would suggest the electro-etching method in diluted hydrochloric acid (10 % HCl in Ethanol). I achieved with about 6 V very good results. But keep in mind that the dark spots you mentioned could also stem from suboptimal polishing.
BR
Dear Preetish,,
you can try alternately polishing and etching.
For etchant try:
Table 3 Electropolishing techniques for wrought heat-resistant alloys
Electrolyte composition Comments
1. 37 mL H3PO4, 56 mL glycerol, 7 mL H2O For Inconel 625, use 1.2-1.6 A/cm2 (8-10 A/in.2); for Incoloy 800, use 3.1 A/cm2
(20 A/in.2); platinum cathode
2. 25 mL H3PO4, 25 mL HNO3, 50 mL H2O For Inconel 600 and X-750, use 17.8 A/cm2 (115 A/in.2), 5-10 s; platinum cathode
3. 144 mL ethanol, 10 g AlCl3 (anhydrous
aluminum chloride), 45 g ZnCl2 (anhydrous
zinc chloride), 16 mL N-butyl alcohol, 32 mL H2O
For cobalt-base superalloys; use 23-25 V dc at room temperature with successive
1-min periods
(volume 9: Metallography and microstructures)
Best regards
Electrolytic etching using 5% Nital at 5V is giving me good microstructure without dark spots.
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