[MW:8891] MW:8886- Duplex S.S - How to reduce ferrite content in HAZ

Mr. Srini,

 

I highlighted some text on the attachment, which I'm sure would be of great interest to you. As the issue is with HAZ I would think the prime  cause/causes are heat input vs. cooling rate.

 

The heat input in the PQR is 42Kj/Inch or 1.7Kj/mm, which is slightly on the higher side, may not a lot. However  a strict interpass of 80 deg C means the cooling rate high which is not allowing the ferrite to transform into austenite.Note Duplex S.S will have high temperature  ferrite phase (see the arrow in page -2) , the primary mode of solidification is ferrite and the cooling rate throughout the transformation zone controls the ferrite : austenite ratio.

 

I would think at the above heat input rate if  the interpass temperature is controlled between 100-125 deg Max, you'll be able to get around 55-65% ferrite in the HAZ.You may check the proper chemistry of the BM and welding consumable, the required level of Nitrogen in addition to Cr,Ni and Mo would help to balance the phases(ferrite and austenite).

 

Thanks.

 

Pradip Goswami,P.Eng.,IWE.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net


-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Srini
Sent: Wednesday, December 22, 2010 11:13 AM
To: Materials & Welding
Subject: [MW:8886] Re: Duplex S.S - How to reduce ferrite content in HAZ

Yes. i am proceeding with G48A to asertain pitting resistance.
However, is there any thing more i can do to fine tune the process itself to get the ferrite in HAZ down?

Thanks
Srini

On Dec 22, 3:16 am, p_chavda...@mail.bg wrote:
>  Dear Mr. Srini,
>
> Two things:
>
> 1. According to me it is strange that you have measured so high  ferrite content, taking into consideration the weld method and the obtained heat input. Are you sure that the ferrite content in the HAZ 71% is.
>
> 2. From what I am reading I am not convinced that there is no loss in  the resistance to pitting corrosion. ASTM C is a good procedure in  terms of determining the loss in the resistance because of  precipitation of intermetallic phases, but not in general. Take into  account, that sometimes even when there are no intermetallic phases,pitting corrosion could appear because of local depletion of Cr, Mo or N, i.e. locally the PREn is less than required. By such high ferrite content, you could expect at least precipitation of Cr2N (there is no enough austenite to dissolve the nitrogen), so I suggest you to perform additionally the G 48 test in order to ascertain that there is no loss.
>
> Regards
>
> Parvan Chavdarov
>
> ----- Цитат от Srini (sethu.sr...@gmail.com), на 21.12.2010 в
> 21:44 -----   Can you please advice some thoughts how to reduce ferrite in HAZ and bring into range of 60% max. This is an weld  procedure development and ferrite was as high as 71% (E562 - Metallography method) in HAZ. Ferrite in parent metal 50%, ferrite in weld metal was 50 to 55%. The details of the processa are as below.
>

Material Dual S32205/S31803. Thickness 1.25" (32mm). Process- SAW. Double butt joint. Parameters 450A/30V/20". Heat input was 42Kj/inch. After each pass i let the part cool naturally to about 80° and then  welded the next pass. i continued the same to keep the cooling rates  consistent. May be i have put too much control and resulted in faster cooling rate and hence high ferrite in HAZ. No intermetallic phases found. ASTM 923 C - no corrosion loss, but the customer would not accept 71% ferrite in HAZ. has to be less than 60%  to avoid pitting corrosion.
>
> Thanks for any help in advance.
>
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