Following this question, I am trying to understand how/if the choice of acid we might use during the pickling and passivation of certain metals, can influence the severity of hydrogen embrittlement. To my best understanding, all etchants will induce some hydrogen ions into the surface during the etching process. However, some believe Citric acid is a better choice than Nitric acid when it comes to this issue.

I tried doing some research but I can not find any relevant reference who has studied this specifically. So my question is how different acids used for P&P of metals can cause different hydrogen diffusions into the surface? My goal eventually is to find the best etchant to remove the wire EDM recast layer on STAVAX (modified AISI stainless steel series 420).


1 Answer 1


The primary cause of hydrogen cracking is a susceptible matrix . Typically a carbon or low alloy steel that is hard ( > HRC 25) untempered is the primary problem. The martensitic chrome steels were very rarely a problem. What is the required hardness ? Likely the simplest remedy is to temper or stress relieve; ideally to below HRC 24. Another remedy is to bake out hydrogen after etching ( one hour above 400 F after etch for thickness less than one inch.)

  • $\begingroup$ thanks for the response. 1. we already know that atmospheric hydrogen should not be a problem for this material (ref) 2. we also know that ~100C bake-out is the canonical way to get rid of hydrogen diffused into the subsurface. 3. the core question at this moment is whether the choice of etchant has any impact on this issue or non at all. $\endgroup$
    – Foad
    May 10 at 8:09

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