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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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AMS 2700 Type II Passivation of Stainless Steel
Current question and answers:
Tip: Readers want to learn from your situation,
often just skipping abstract questions.
Q. Type 2 vs Type 6 per AMS2700
-Other than Type 2 containing Sodium Dichromate on Medium Temperature. What are other detailed differences between Type 2 and Type 6.
- Fullerton California
May 10, 2021
A. Hi Bobby
Usually type of passivation is selected per manual's request.
Also, type 6 has a little higher concentration of Nitric acid.
If you take a look on the last page of AMS2700, there is a list of recommended passivation types in accordance with type of alloy. Type 2 is recommended for almost any stainless steel or corrosion resistant steel, while Type 6 is not recommended (per AMS2700) for Ferritic, Martensitic and Precipitation hardened alloys.
- Winnipeg, Canada
May 13, 2021
A. The differences in the two types are as follows:
Type 2: 20-25% vol nitric, 120-130 F, 20 minute immersion time (plus 2-3% by weight sodium dichromate)
Type 6: 25-45% vol nitric, 70-90 F, 30 minute minimum immersion time
In our shop we use Type 6 as it's easier to maintain (less power to heat and only one chemical to deal with).
Hope that helps
- SLC Utah
May 14, 2021
⇩ Related postings, oldest first ⇩
Q. We are quoting passivation of a medical device manufactured from 17-4 H-900 stainless steel. Is anyone aware of any restrictions on the use of nitric acid w/ sodium dichromate to passivate medical devices.
We are set up for this process but not the high concentration-high temp nitric process.
- Colorado Springs, Colorado, USA
2007
A. Type II passivation works well with 17-4. I personally prefer the type VIII because I don't like mucking about with the sodium dichromate. Yet I never had any problems when we did use type II, and a few of our parts were H900 condition.
Lee Gearhart
metallurgist - E. Aurora, New York
2007
Q. REF: 416 SS passivate per AMS2700 Method 1, Type 2.
Hello, we've sent many parts to our different passivation vendors and keep getting parts that are "Flash attacked" or etched. This has been a hit and miss for us with the different companies. Is there anything we can do or suggest so that this doesn't continue happening?
Jessica Fritter- Fort Lauderdale, Florida, USA
September 28, 2016
A. Hi Jessica. I don't know if your company must comply with this job requirement or you are the author of the job requirements. If the latter, you can probably solve the problem by changing the spec to citric acid passivation, or electropolishing, or something else if you are the author of the requirements and you are not in aerospace.
If your vendors must comply with AMS2700 Method 1, Type 2, one suggestion is that the parts be cleaned better before passivation because some people claim that even minuscule traces of oils can cause this etching, perhaps by generating some sort of organic acid which etches the parts.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2016
Passivation, but not per AMS2700 E suggested type
Q. Hey,
I'm creating a passivation series of tests for this, I have to passivate various CRES steels. But I have a Problem with the steel 1.4034 (AISI 420/UNS Code S42000).
In the Standard AMS2700 E it's recommended to use Method 1 Type 1-3 (citric is no choice for us), to passivate the specimen. But our favorite choice would be Type 8. Do you have any experience in passivating parts unlike in the AMS suggestions? Do we have to expect degradation of the mechanical properties or something similar?
Greetings,
David
materials student engineer - Pfäffikon, Switzerland
November 4, 2016
A. David,
Go ahead and try a small piece of 420 in the Type 8 bath. You'll probably see for yourself why it's not a good idea. (Usually mismatching nitric bath types and stainless grades results in the part being ruined and/or emission of large quantities of toxic NOx gas.)
Citric passivation does have the advantage that if you set it up properly, you can use one bath to handle all your different grades.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
November 7, 2016
November 30, 2016
Q. Hey guys,
thanks to your input. I persuaded my Supervisor to at least try the citric solution for the 1.4034.
Our common passivation suppliers don't have much experience with citric acid and asked us for the desired bath temperature/immersion time, citric concentration and whether the bath Needs "additional wetting agents and Inhibitors as applicable".
Do you have any recommendations for us (a little bit more detailed specifications than these in the AMS2700 would be great)?
Thanks a lot,
David
materials student engineer - Pfäffikon, Switzerland
A. David,
The parameters you are asking about are given within the 2700 standard, though for 420 you're probably going to want to be at 20 minutes or more even at 65 °C. Of course testing with your parts against desired performance levels is recommended as well.
As far as the additives, they aren't absolutely necessary, but I like to think they do help quite a bit, since that's essentially what my product is. If you are interested, click the link next to my name and you can get my contact information, then I can direct you to my distributor in Germany.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
December 2, 2016
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