PWHT of 4140
PWHT of 4140
(OP)
I am preparing to perform a PQR for a WPS for the welding of 4140 casing. The WT of the coupon is .5". Processes used will be GMAW ER80S-D2 root and SMAW E10018M (H4) fill (butt weld). Pre-heat will be 450F. The "PWHT" that has been recommended is 950F +/- 25. The base material was quenched and tempered at 1173F. It has also been instructed that we put the coupon into the oven as soon as possible after welding, I think they are worried about cracking after welding. It's my belief that the worry about cracking stems from the how the production pieces are to be welded. There are components that will be welded to the external surface of the casings with 2 - 6" long, one pass 1/4" fillet welds.
There are a few issues that we feel are at play here. One is 950 is not really a PHWT temperature for this material, it's more of a "bake out" for hydrogen considerations. Another is that we're worried about not allowing the material to go through it's microstructure transformations as it cools after welding.
Opinions and advice?
There are a few issues that we feel are at play here. One is 950 is not really a PHWT temperature for this material, it's more of a "bake out" for hydrogen considerations. Another is that we're worried about not allowing the material to go through it's microstructure transformations as it cools after welding.
Opinions and advice?





RE: PWHT of 4140
RE: PWHT of 4140
RE: PWHT of 4140
To further this, we plan on doing either a hot wire GTAW or pulsed GMAW WPS once we've met the requirements of the first procedure. Since both processes have almost no hydrogen present and the current PWHT is not high enough to stress relieve, would the 950F PWHT not even be required because there is no hydrogen present? Of course this is all hinging on if the PWHT is ACTUALLY currently being done at 950F. This is a detail that hasn't been shared as of yet with us as of yet.
If it is being completed in the 1100-1150F range then this part of the question is moot.
RE: PWHT of 4140
No.
I think the 950 deg F PWHT was selected because someone wanted to remain well below the original tempering temperature, I have seen this before. I don’t believe this is a hydrogen bake because hydrogen can diffuse at or above 450 deg F. Don't believe any welding process is hydrogen free, hydrogen can be introduced from the wire; yes the wire manufacture, and surrounding atmosphere.
RE: PWHT of 4140