iron oxide analysis

[fusitexa]

hi, all,

we have an un-abnormal corrosion happened on the surface of a SS400 plate, and i would like to ask you guys to give me an instruction on how to analyze the oxide. i will post a few photos of the oxides to you for your reference. the corrosion plate was returned from the customer and what i know is no higher temperature and dry atomsphere condition. thanks in advance.

BR

 

[fusitexa]

one more photo. the morpholoyg of oxides is unexpected to me.

 

[mrfailure]

This certainly looks like hematite based on what we see visually. You can certainly scrape the deposits and have them evaluated using energy disppersive spectroscopy (EDS) to see if there is more than just iron oxide and elements expected from your steel alloy. You can also check the alloy using PMI (aki portable XRD) to make sure your steel really is 400SS. Destructive examination, if allowed can get you more information such as quantitative chemistry and morphology of corrosion attack.

 

[EdStainless]

I would really be looking for the Cl or S in the rust that caused it.
Do you know the parts history? What has been dripping onto it?
Are there a bunch of these in identical service? Is this the only rusted one?
Are you certain that it was properly passivated before it went into service?

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P.E. Metallurgy, Plymouth Tube

 

[mrfailure]

My bad - I meant to say portable XRF when I mentioned PMI.

 

[fusitexa]

mrfailure, and ED, thanks for your reply.
the part has not been used in service, it was just fixed to the customer's equipment. and the time is no longer than 1 month. as for what dripping on the part, sorry, i dont know it and i guess the customer really didn't know. what i will do is as mrfailure said, EDS, chemcial test of the body.
thanks again.

 

[fusitexa]

i made the cross section examined with SEM/EDS method. and i found that there is a Ni-P plating, however, it didn't protect the body from corrosion. and i also EDS test the oxide layer on the surface, and its mainly elements is O and Fe, and its AT% is about 78% and 21%, and no S and Cl was detected. attached photo is SE photo of the cross section.

 

[mrfailure]

What about the substrate? You should be able to confirm this was a 400-series steel by an EDS check of the base metal, though a full quantitative chemistry would be better.