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[MW:15173] Defects in the MIG welding of F91+F91 -reg

By Materials & Welding
Dear friends,

I am working the leading valve manufacturing company in Coimbatore ( INDIA) i ma facing quality issue in the MIG welding of Er 90S-B9.
We have product in ASTM A182- F91 forged steel valve ( Equivalent to C12A casting or P91 pipes),during welding of body+Bonnet we are facing the crack in the crater area.
Our welding parameters are as below:
Joint type = Circumferential Fillet welding, Current = 215 - 235  Amps, V = 25 - 27 Volts, Shielding Gas = Ar+CO2 ( 80+20 % mixture), Gas flow = 20 - 25 LPM, Pre heat temp =  210 - 230 Deg C, Inter pass temp= 320 - 380 Deg C
>After welding ,the joint was inspected by M.P test andcrack found on crater area.
> Removed the welding by turning, then re- test carried out with increased
the post flow timings of shielding gas, but no improvement in the test, same
crack appeared on crater area.

What will be the reason for this defect? Can you suggest me suitable method
to over come this problem?
What will be the reason for this crack?
Kindly send your recommendations to solve this issue.

Advance thanks and regards,
Sankaran.SP
 

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