ETCHING

Etchant Composition Concentration Conditions Comments
Kalling’s No:1 Distilled water CuCl2 33 ml Immersion etching at 20° C For etching martensitic stainless steels. Martensite will be dark and the ferrite will be coloured
HCl 1,5 grams
Ethanol 33 ml
Kalling’s No:2 CuCl2 5 grams Immersion etching at 20° C For etching duplex stainless steels and Ni-Cu alloys and superalloys
HCl 100 ml
Ethanol 100 ml
Kellers etch Distilled water 190 ml 10 –30 seconds immersion. Use only fresh etchant Excellent for aluminium and alloys immersion for 10 – 20 seconds; titanium alloys immersion for 10-20 seconds
Nitric acid 5 ml
HCl 3 ml
HF 2 ml
Kroll’s Reagent Distilled water Nitric acid 92 ml 15 seconds Excellent for titanium and alloys. Swab specimen upto 20 seconds.
HF 6 ml
2 ml
Nital Ethanol 100 ml Seconds to minutes Most common etchant for Fe, carbon and alloys steels and cast iron- immerse sample up from seconds to minutes; Mn-Fe, MnNi, Mn-Cu, Mn-Co alloys, immersion upto a few minutes.
Nitric acid 1-10 ml
Marbel’s Reagent CuSO4 10 grams Immerse or swab for 5-60 seconds For etching Ni, Ni-Cu and Ni-Fe alloys and superalloys. Add a few drops to H2SO4 to increase activity.
HCl 50 ml
Water 50 ml
Murakami’s K3Fe(CN)6 10 grams Pre-mix KOH and water before adding K3Fe(CN)6 Cr and alloys (use fresh and immerse) iron and steels reveals carbides. Mo and alloys uses fresh and immerse; Ni-Cu alloys for alpha phases use at 75°C; W and alloys use fresh and immerse; WC-Co and complex sintered carbides.
KOH 10 grams
Water 100 ml
Picral Ethanol 100 ml Seconds to minutes Do not let etchant crystallize or gry-expolisive Recommended for microstructures containing ferrite and carbides.
Picric Acid 2 – 4 grams
Vilela’s Reagent Glycerol 45 ml Seconds to minutes Good for ferrite- carbide structures (tempered martensite) in iron and steel.