Chromium carbide of 321 stabilized stainless steel

[kowngs]

I've had a exprimental test for 321 stainless steel plate and welds if chromium carbides of 321 stainless steel can be removed by solution annealing.
I chose specimens that thickness is 52t plates and welded as per ASME code.
And the specimens were exposed 450 deg for 4 hours to create chromium carbides.
After exposing sensitized temperature (450 deg), microstructure showed chromium carbides in grain boundary.
Then, the specimens were solution heat treated in 1,060 deg. for 2 hours (according to ASM recommandation).

As I know from ASM code, heat treamtnet above 1,000 deg. will removes chromium carbides.
But, result shows that chromium carbides in welds are not removed.
Yes, chromium carbide of base metal and some of chromium carbides in welds are gone, but lots of them in welds is still not removed. Finally, it fails A262 test practice E.

Here is my question comes up. If 321 stainless steel with welds are sensitized (with chromium carbides), chromium carbides can be removed by solution annealing? Is there other ways to remove?
Or just it can not be removed?

 

[kowngs]

Dear Martinos

As I said before, weld material is AWS A5.4 E347.16, and C composition of weld material is 0.06%.
That C content is not low in my opinion.

So, you think those globular particles are not NbC? or CrC?

 

[Martinos]

Dear,
carbon content 0.06% is definitely too low to reach such coarse carbides. Moreover, chromium rich M23C6 carbides typical for low carbon stainless steels are not only very fine, but also mostly on the grain boundaries after slow cooling. After rapid cooling they are within the grains and in that case they are practically invisible by magnifications like these. In your case, after solution annealing with rapid cooling, carbides like Cr-rich M23C6 have to be within the grains, but very fine.

Regarding chemical composition only M23C6 carbide or complex carbonitrides can be expected in matrix. The globular particles as I saw are definititely too coarse to be M23C6 in steel with 0.06% of carbon. Carbides with size like in your photomicrographs can be seen after spheroidizing of carbon steels...

 

[Guest102023]

TiCN particles are also orange or gold in colour, making them easy to spot.
There is not necessarily any connection with grain boundaries in my metallographic experience.

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