Problem with SS304L flange 1

[Naruwan]

Hi, our client had a problem in his solution annealing problem with his 304L flange. Size: 6inch diameter with 0.8inch thickness and 300 pound force. He stated that he heat treated his flange at 1050 degree celsius and held at that temperature for an hour.

However, looking at the cross section's microstructure (as attached), it seemed that the twinned grain grain size are not that equiaxed. Grain size seemed to be slightly bigger at sub-surface level. Is the solution annealing process done properly? Thanks!

 

[metengr]

No. It would appear the time at temperature for solution treatment was too short.
Did the client measure the time when the metal temperature reached 1050 deg C and held or when the piece was placed into the furance?
What kind of furnace was used?
How accurate was the temperature measurement in the furance?
How many furance TC's were used?

 

[Naruwan]

Hi metengr,
We were provided with very limited information about this flange by my client, therefore it's getting tough for us to investigate the whole matter. Let me ask again over the weekend.

Attached is another photo which I took. This photo was a picture of a part of the flange. This is a picture of the flange as received condition from our client. Do take notice
of the weird greenish colour and those black and white patches. Client claimed that all these came out after they did the solution annealing and water quench.

 

[metengr]

Naruwan;
It looks like the one side of the flange in your picture was subjected to welding. The local areas of discoloration on the surface appear to be areas of either direct flame impingement or areas where surface contamination was present when the flange was subjected to heat. It also appears the surface has small beads of weld spatter.

 

[EdStainless]

My guess for the surface discoloration is that the flange was not clean before annealing.
If the part was water quenched from anneal then it should have been pickled to remove the oxide that formed. That could be the green tint.

As to the micro, it may not be a great anneal but it meets all of the specifications. Unless there is a significant amount of delta ferrite or transformation martensite in the structure then it is fine.

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Plymouth Tube

 

[EdStainless]

I should add also free from grain boundary carbides, but it looks like they took care of that.

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Plymouth Tube

 

[Naruwan]

Talking about grain boundaries, I did a light polishing directly at the white spots are and this is what I got as attached. It seemed to be more like oxides (from heat treatment) than chromium carbides and these are happening on the white spots area. Furthermore, these black stuffs were not actually affecting the sub-surface microstructure, which was shown in my previous posts. I also noticed that the grains at the affected areas are not twinned. Is this a sign of improper heat treatment too?

 

[metengr]

Naruwan;
If these are indeed intergranular oxides, this would confirm some type of surface contamination was present prior to solution annealing or a poorly controlled furnace atmosphere.

As far as improper heat treatment, this depends on the end use of the flange. Overall, the solution anneal may be acceptable based on the appearance of the microstructure internally. If this flange is required to perform in a service environment where all exposed surfaces are required to be free of intergranular oxides, then you have a nonconformance and this needs to be addressed, either by surface machining to remove these areas or other approach.

 

[EdStainless]

Are you sure that those weren't oil spots and that you are looking at intergranular carbides from sensitization?

I am with my friend, you need to know how deep they go.

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Plymouth Tube