Recommended passivation method for 303 SS

[dchu129]

What would be the best method to passivate 303 Stainless Steel?

In order to get a good clean on the material, it is placed in

1) electro chem (with current) to remove oil
2) phosphoric acid
3) passivate solution

however, the phosphoric acid will react with 303 leaveing a stain on 303; without phosphoric acid, part will have sign of rust in salt chamber.

 

[Metalhead97]

dchu129,

The phosphoric acid is there to act as a chemical polishing or etching solution depending on whether you get good leveling or not. It's used to remove material indiscriminately to prove a 'fresh' surface for the passivation solution to act on. Try adding an oxidizer such as nitric acid or H2O2 to help 'drive' your reaction so that all oxide films are unstable. Be careful H2O2 needs to be kept at room temperature or it will break down and create a dangerous mess!

metalhead

 

[swall]

Carpenter recommends 20% HNO3 with 22g/l of sodium dichromate addition. Time is 20-30 minutes.

 

[Metalhead97]

swall,

I think the question pertains to the chemical material removal step using perchloric acid, but I could be wrong.

metalhead

 

[EdStainless]

Are you doing the initial cleaning in an alkaline?
you then rinse well?
I would seriously look at using nitric acid for passivation.
20-25% just warm, not hot. (100-120F)
DI water rinse after.

You may always get some staining from the attack of the inclusions in the 303. The help machining but reduce corrosion resistance and mar the appearance.

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