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Letter 20049
304L Acid Etching Problem not found in
the Archives [Arizona]
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We are having a problem with acid etching 304L Stainless Steel.
The etch mixture is 20%v/v HNO3 and 3%v/v HF, remainder DI Water.
When regular 304 Stainless is put in this bath, there are no
problems. But, when we put in 304L Stainless in the bath we find
micropitting, discoloration and some type of film is left on the
surface. There are no surface contaminants when the material is put
into this bath and the tooling used on this material in the machining
process is the same as for the 304 Stainless. I have searched the
archives and found nothing that addresses this issue.
Is this a problem that other metal finishing shops have??
Any input would help. Thank you in advance.
Ron Simpson
- Phoenix, AZ
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Ron-
With the 3% HF in there you will expect some microetching of 304
AND 304L. I am not surprised that the low carbon grade etches more,
but I do not have any data on this. There must be a metallurgist out
there that can explain it. Are you removing heat treat discoloration
with this mixture?
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Dear Ron,
I have a question regarding to your pickling process. Do you have
a recycle system or acid recovery system in your factory. Or what
kind of methods do you use to dispose the depleted waste acid and how
do you treat the sedimented metal such as Fe, Cr and Ni compounds?
Pinar Hasanoglu
- Turkey
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