[MW:7473] Duplex 2205 welding - High ferrite

Hi Srini,

 

A change of backing gas from 100% to Ar+2% O2 or Ar+5%N2 could be beneficial. The ferrite required vs. ferrite obtained are not very far apart. The reasons for suggested change are as specified below:-

In a duplex stainless steel, nitrogen plays major roles such as  to contribute to the resistance to pitting corrosion. There's  loss of N in the weld surface, especially with GTAW and GMAW  method  when pure Ar is used as shielding gas, though pure argon is is satisfactory for most applications.

When pure Ar is used, the loss of nitrogen  is in the magnitude of 0.03–0.05%, typically at the surface of the root bead and at the parent metal 0–1 mm from the fusion line .When maximum resistance to pitting corrosion is required, nitrogen bearing shielding and root gases should be used to compensate for the loss of nitrogen. Typical recommended backing  gases  are  Ar + 2–3% N2 , or Ar + 5% N2. 

I would say a switch to Argon+5% N2 could lower the ferrite by pushing up the austenite in the weld/HAZ..

I extracted from  presentation on duplex s.s from Sandvik. Note the the effect of Nitrogen on the phase balance.

Thanks

Pradip Goswami,P.Eng.

Welding & Metallurgical Engineer/Specialist

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Sridharan Chandran
Sent: Saturday, October 09, 2010 1:57 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:7465] Duplex 2205 welding - High ferrite

Srini,

 

I would suggest 100% Nitrogen as back purging gas to achieve reduced root ferrite i.e. witihin acceptable limits.

 

Sridharan

Welding & Metallurgy - Consultant Engineer, Perth

On 9 October 2010 00:05, Srini <sethu.srini@gmail.com> wrote:

Hello, Need some help here.

Pqr was developed with GMAW STT root and FCAW fill. Filler metals were
ER2209 and E2209T1-4.
Shielding gas Mison 2C (98+2Co2) for STT, Mison 25C (98+25Co2) forFCAW. Impacts, Corrosion per A923 Method C passed. However when
metallographically tested for ferrite count per ASTM E562 we found the   ferrite content in root HAZ was as high as 69 - 70%. Typically we   would like to achieve 60 or 65% for better corrosion properties. Heat   input root pass= 25Kj/inch and fill passes=35Kj/inch. Backing gas was   100%Ar.

Any suggestions for reducing the ferrite content in HAZ of root is
welcome. Thanks in advance.

Srini

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