Duplex weld micro structure anomaly

[Liuk]

Dear colleagues,

Could your help me evaluate/understand micro structure anomaly (please find attached)?

This is DSS weld cup microstructure (photo TV31, TV32) and SDS one (photo SDD_weld) . Welded joint is in solution annealing condition.

It seems sigma phase formation, but very coarse (magnification was 500x). I have etched it by NaOH 15 sec (for attached photo). Etching by NaOH during 2 sec have given the same result as well as etching by Beraha's (white "island" in blue ferrite).

Am I right? I observe structure like this in the first time (we examine DSS/SDS in different condition very often...)

What is reason of formation this microstructure?

Thank you in advance

 

[OGMetEngr]

I'm only seeing one file uploaded. Can you upload the others as well? And what happened to that first micrograph? Are you saying that is a weld cap?

 

[Liuk]

Hello,

I can attach only one picture.

Tv32 is cup (last run) weld metal microstructure.

 

[jwhit]

Is that your electrode contact point? The discoloration and circular shape point me in that direction. If so the microstructure has been distorted by localized heating.

 

[EdStainless]

Or is there some localized contamination?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Liuk]

I have attached photo of SDD weld.
If the first photo is weld surface, the second and this one is in 2 mm from weld surface. Welds was performed by SAW.
It is local microstructure changing.

 

[Guest102023]

Sigma phase would not appear in a normal weld cycle.
My first impression was a very small arc strike, very unlikely with SAW.
Looks like a spherical inclusion. You may not see it again in another 100 tests.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[kjell123898]

hi,

I'm seeing only a normal structure formation consisting of austenite/ferrite in a normal distrubution (spacing) with no traces of neither sigma nor chi phases on this image, but where are the other ones??

Kjell Grønvold

 

[Liuk]

I have attached photo for DSS weld. Etching time 2 sec (NaOH), magnification 1000. I think intermetallic phase is seen clearly.

Hardness in this point was 305HV10 vs 245HV10 for BM.

 

[kjell123898]

hi again,
These images are misinterpreted because the circular spot placed as a burned on layer outside austent / ferrite structure is probably something deposit after the initial polishing and etching was performed.
So from my point of view it seems to be a drop of transfer that is stuck on an already micro processed duplex structure

Kjell Grønvold

 

[Guest102023]

Aha, possibly an arc strike from the electrode used to electrolytically etch?

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[jwhit]

Brimstoner is describing exactly what I was trying to describe, but did a better job of it. I've seen it many times, in various stainless steels. If that is where the electrode made contact, discount that area as being a valid structure. I found that drilling into the side of the mount to a depth that contacted the specimen would allow me to place the electrode against the specimen without interfering with the etched surface. Gives a much more uniform etch.

 

[Liuk]

What is interesting assumption!

We use LectroPol5 (Struers) for etching (no "direct contact" examined section with electrode). We examine about 5-10 sample in day. Other sections were without any surprises.

I think it can't be caused with etchant problem, but I can understand reason of formation this structure.

Two "points" were on examined section of DSS weld: one near surface, other in 2 mm from weld cup surface and 10 mm between points...

 

[Liuk]

And one more comment: voltage 2B, current 0,18 A. No any jump on current/time curve.