Welding then forming 409SS problems

[gilley29]

Weld seam cracks after roll forming a flange.

Process: Rolling a cylindrical tank with 14 ga 409SS sheet and
using SAW for the butt weld seam. Filler is ER309LSI and flux is
ST-100. After the seam weld, a .4" deep flange (rough cross
section below) is roll formed on the top edge of the tank. The
weld is so brittle it cracks at the stressed corners. I am getting
mixed info on pre- and post-weld heating. One says to use low
heat input during welding and form at room temp without
annealing. Another expert suggested pre- and post-weld
treatment. If heat treatment is recommended, can heating with a
dull grinder be effective? Any other suggestions? It would be
nice if a ductile filler for 409 and 304 could be found. Thanks in
advance. SCOTT

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[jackboot]

Scott:

Is 409 a Martensitic or Austenitic Stainless?

If Martensitic- try this:
1. Preheat to 400 F minimum
2. Heat treat or anneal the part (1550 to 1650F for two hours then slow cool at rate below 100F per hour).

You might see if you are cold working the material with your weld seam. Welding will input thermal stress which can be compounding the problem.

jackboot

 

[gilley29]

It's actually a ferritic grade. NIDI recommends no preheat for thin gauge. They recommend annealing at 1450F then slow cool to 1100F, than a rapid cool. Slow room temp cooling induces brittleness (i guess). Thanks for your response.