Summary for astm a967 nitric 1 Discussion
Passivation of 300 series steel with ASTM A967 Nitric 1 is discussed in the context of Figure X1.1, which lists Nitric 2 and 3 as the recommended methods for austenitic 300 series grades. John Wooldridge asked why Nitric 1 is not recommended and whether it could be detrimental, noting he only had an approved vendor for Nitric 1. The reply says there is no specific knowledge of the rationale behind the different nitric baths, but warns that mixing the wrong grade with the wrong bath can destroy parts and even trigger a runaway reaction with toxic fumes. The practical advice is to test the parts in Nitric 1 and proceed only if the results are acceptable. The answer also notes that citric passivation is an alternative for 300 series stainless and avoids the concern of using the wrong bath.
August 28, 2013
Q. Figure X1.1 of ASTM A967 shows Nitric 2 and 3 as being the only recommended methods for austenitic 300 series grades of steel. Currently, I do not have an approved vendor for either Nitric 2 or 3 processes, only Nitric 1. My very limited research seems to indicate that Nitric 1 would merely be overkill for 300 series but not necessarily detrimental. What is the rationale behind Nitric 1 being not recommended for these grades of steel? Could it be detrimental?
Thanks in advance.
John Wooldridge
– Maumelle, Arkansas
A. John,
I don’t have specific knowledge of the rationale behind the different nitric baths. I do know that playing mix and match with the wrong grade in the wrong bath can result in destroyed parts and/or a runaway reaction that produces a cloud of toxic fumes.
If you can test your parts in the Nitric 1 bath and are happy with the results, then go right ahead with it.
Of course citric passivation is always an option too, and you’ll never have to worry about having the “wrong bath” with 300 grades in citric.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
September 24, 2013