Super Duplex - Where did the Nitrogen go?

[iam42]

Hi,

I have just completed a PQR for Super Duplex (S23750) using ER2594 GTAW wire, 100% Nitrogen backing gas and 100% Argon shielding.

Test coupon - 10" Pipe x 0.30" thk

The test results were good and shown below:

Tensile: 119,800 & 120,700 psi
Charpy Average @ -50°C: WM 119 ftlb, FL 76 ftlb, FL+2 90 ftlb, FL+5 134 ftlb, Base 130 ftlb (Subsize: .276" x .394")
Face & Root bends acceptable
Ferrite point count: HAZ Root 43.75, HAZ Cap 56.25, Weld Root 44.5, Weld Cap 56.13,
No evidence of Intermetallic phase
ASTM G48 A: No evidence of pitting, Weight loss 0.2746 g/m2
Hardness: Max Value 319 HV10 (weld metal root)

Now the problem I am seeing is with the Nitrogen level in the chemical analysis.

C: 0.012 Mn: 0.41 P: 0.017 S: <.001 Si: 0.40 Cr: 24.8 Mo: 4.00 Ni: 9.1 Cu: 0.06 N: 0.15

Base Metal N content = 0.2752
Weld Wire N Content = 0.25

Can someone help me understand why it is so low?

Thanks

 

[EdStainless]

Did you have all three analysis done by the same lab at the same time?
From the properties there obviously is enough N2.
Send all three samples to your lab and have them re-analyzed.


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P.E. Metallurgy, consulting work welcomed

 

[iam42]

Thanks Ed,

The mechanicals and chemical analysis were done about 2 weeks apart. They were carried out at the same Lab.

There was no analysis done of the base material or the weld wire, I am using the values from the MTR's

The analysis was only carried on on the finished weld.

It certainly has me scratching my head.

 

[EdStainless]

Light elements (N, O, B) are notoriously difficult to analyze.
We always rechecked them.
The values from the plate and wire are likely heat chemistries that were taken before casting.
Having good check chemistries is always nice.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed