Chrome carbide diffusion?

[nawlins]

Why would a piece of 3166ss have a 26% chrome content after it has corroded? Is this what is known as chrome carbide diffusion.

 

[JoeyV87]

Well, it depends what you mean by "have a 26% Chromium content". It could be that you are analysing what is left over after severe corrosion, which is likely to be regions of higher Chromium content. It could also be your analysis technique, or it could be that you have sampled a spot of sigma phase or similar.

 

[nawlins]

All of the areas like that read the high chrome content. These areas are also a dark red like a dark colored rust but it is in tact and hardness values are in the 600 vickers areas.

 

[weldstan]

Are you sure the material is 316 SS? This level of hardness is inconsistent with 316SS. Was it nitrided?

 

[IRstuff]

unless you've exposed the steel to very high temperatures, I can't see any metal moving around in the lattice. see:

http://appliedthermalcoatingsusa.com/images/Chrome-DiffusionStudy.pdf

for temperatures involved in getting even a surface chrome treatment.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[nawlins]

Thanks all