I have recently read a very informative article on passivation at www.pfonline.com, however I did not recall seeing anything specific to 420 stainless. Will proper passivation prevent oxidation of this material? K.W.
You can passivate 420 stainless steel. Since it has a relatively low chromium content (12-14%) and elevated carbon to aid in machining (greater than 0.15%), you should use a passivating solution that contains a small amount of sodium dichromate to ensure the bath does not start to etch the parts. A recommended starting solution of about 20% by volume nitric acid and 5% by weight sodium dichromate could be used. You will need to use caution with this mixture due to its corrosivity, oxidizing potential and the toxicity of the chromate. Make sure that the process complies with workplace and environmental regulations.