Cronidur 30 Etch
Cronidur 30 Etch
(OP)
I have a part that came in for a metallurgical inspection made of Cronidur 30 (aka N360 Iso-Extra and AMS 5898). We have tried etching in both Nital and Vilella's, our standard etchants for most materials. Neither reveals much of a structure and the part also seems to have scratches afterward. Can anyone recommend a microstructure etchant for this corrosion resistant material?
Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast





RE: Cronidur 30 Etch
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I did not find much information regarding etchants for this HNS martensitic stainless steel. I would recommend you contact Buehler, specifically, George Vandervoort for etchant techniques/recommendations.
http://www.buehler.com/
RE: Cronidur 30 Etch
Thanks
Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast
RE: Cronidur 30 Etch
I'm not sure if you or metengr noticed, but the authors of the article from the above link described the etchant that was used (2nd to last paragraph on page 137). I have not personally used HF + molybdic acid (MoO3) as an etchant, so I cannot give any advice as to its usefulness for this alloy, but boiling HF is not your everyday lab chemical.
I don't think nital by itself will etch this alloy, but maybe adding some HCl to it would improve the response. I would try 5-10% nital + 5-10 mL HCl. Another option would be to revisit the Vilella's etch, but to use a different ratio, such as the one suggested by Struers in the following Application Note:
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One suggestion from GVV and Buehler for etching martensitic stainless steel is modified Fry's reagent (150 mL H2O + 50 mL HCl + 25 mL HNO3 + 1 g CuCl2). Here is a link to some of their technical information on etching:
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By the way, I am not sure that GVV works for Buehler any more. The latest issue of Industrial Heating has an article authored by him, but it shows his affiliation as a consultant to Struers. I haven't tried to contact him to confirm his whereabouts, so if anyone else does, please share with the group.
RE: Cronidur 30 Etch
5-10ml HCL (35%)
1-3ml selenic acid
100ml ethyl alcohol (95%)