Etchants for Carbides in Steel

Figure 1: Etchants for carbides in steels.

Klemm’s I – Colors ferrite, limited to carbon and alloy steels.
Beraha’s “B0” – Darkens matrix in carbon, alloy steels, tool steels and martensitic stainless steels.
Beraha’s Sulfamic Acid No. 4 – Colors matrix in tool steels, martensitic and PH stainless steels.
Alkaline sodium picrate – colors M3C and M6C.
Murakami’s, 20 °C – colors M2C, Outlines and colors M6C, attacks M7C3, faintly attacks M23C6.
Groesbeck’s, 20 °C – colors M2C, outlines and colors M6C.
1%CrO3, 3 V dc – Outlines M2C, colors MC, outlines M23C6, outlines and attacks M7C3.
10% Ammonium Persulfate, 6 V dc – Colors M23C6 brown, not well documented.
Murakami’s outlined and colored M7C3 rather rather than attacking them.
Murakami’s M23C6 carbides rather carbides rather than faintly revealing.
Groesbecks’s did not attack, or reveal, M23C6 as claimed.
Groesbeck’s faintly revealed M7C3 and outlined and outlined M2C, rather than attacking them.
CrO3 outlined M7C3 (as claimed), but did not (as claimed), but did not attack them, as claimed.

Reference: George F. Vander Voort, et al., Use of Selective Etchants to Identify Carbides in Steel, Power Point Presentation, 2008.

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