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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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304L Acid Etching Problem
Q. 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, Arizona
2003
2003
A. 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?
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
Q. 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
2003
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