How heat tints will affect passivation

[MagBen]

The thin (.005'') PH stainless strip got heat tints after H2 anneal. Material will be aged and then acid passivated.
Do the heat tints have a negative effect on passivation? Or, it does not matter because the acid could eventually clean up the tints?

 

[EdStainless]

Straight passivation (such as with 25% nitric acid) will dissolve free Fe from the surface allowing the stainless to naturally form a passive film.
This treatment will not remove the heat tint oxide.
How much this hurts corrosion resistance depends on how thick the oxide is.
If it is thin (yellow or gold and very shinny) then it won't hurt much.

The other question is what is wrong with your anneal?
Why is there any tint?
If corrosion resistance is an issue then you may need to use a light pickle to remove the oxide.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Ed, thanks for reply!
Material is too thin for acid clean. Material is slightly discolored (gold color), I will push back customer to try, otherwise I will have to scrap.
Pickling solution is mainly acid too (HF, HNO3 etc.), why do you think pickle can remove oxide, while passivation cannot?

By the way , this is custom 455 with >1% Ti that makes it very easy to be discolored. you cannot make the furnace perfectly with dry, pure H2. To remove TiO by anneal, say at 1000C, H2 need to be as dry as < -200F.

 

[EdStainless]

We pickle these alloys, just don't heat the pickle solution.
Maybe lower the Hf also.
You need the Hf to cut the oxide.
Yes it is hard to age these without any tint.
After all if corrosion resistance is a big deal they wouldn't be using C455.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube