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.)
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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