Sunday, December 26, 2010

Re: [MW:8948] Duplex S.S - How to reduce ferrite content in HAZ

Dear All,
 
I just keeping the continuation of past query about ss. when we did PMI at HAZ and weld joint,found dissipating in Nickel and Chrome percentage. what is the reason for this? high heat input may change the chemical percentage,we not sure about this.
 
kindly give your feedback on above stated.
 
regards


 
On Thu, Dec 23, 2010 at 1:21 PM, joshi jaydeep <jaydeep.p.joshi@gmail.com> wrote:

The ferrite in weld metal  and HAZ is controlled by  either chemical composition or cooling rate (Thermal  condition).Higher cooling rate gives higher % ferrite in HAZ.(Refer D.J.kotecki  book for ref.)

·         Addition of N,Ni like Austenite stabilizers in DSS help  to  promote austenite transformation and phase balance. So in your case go through the composition of Plate,Wire and flux used.

·         Recommended heat input is below 1.50 KJ/mm, but technical papers says that there is not much effect of high heat input on mechanical and corrosion properties.

·         General observation of ferrite % is the  value is nearly same  in HAZ and  Weldments, but in your case it is too  high.

·         So it needs to cross verify  the ferrite check by point count, Image analyzer or if possible then by ferritoscope (magna gauge).

·         FN to %( percentage) Ferrite ratio is nearly  70% (Example If 100 FN nearly equal to 70% Ferrite)

·          Your sample should be recheck for ferrite value and better to  see then microstructure for getting the actual  idea ,that  what  happen in HAZ.

·         You should also follow all recommendation given by Plate mfg. wire and Flux mfg, before, during and after welding.Like precleaning, interpass temp.etc…

·         Please provide more information about testings and welding details( Consumable types etc.)

Regards,
Jaydeep

On Wed, Dec 22, 2010 at 1:14 AM, Srini <sethu.srini@gmail.com> wrote:
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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