interpass temp

[sftyvlv]

If austenetic stainless develops carbide precip at 450C and up, why does my weld data sheet require my interpass temp to be 300F.
This is 304L sch 80 pipe. Gtaw 308L root, Smaw 308L fill and cap.
Thanks
Sftyvlv

 

[metengr]

sftyvlv;
To avoid excessive heat input in the weld region. This interpass temperature is typical, and has been proven by expierence to reduce susceptibility to carbide precipitation in 3xx stainless steels during welding.

 

[stanweld]

To avoid carbide precipitation at the grain boundaries (even in low carbon stainless), rapid cooling below 800F is required. Low interpass temperatures are effective means of obtaining that fast cooling rate. The thicker the material the more rapid the cooling given the same low interpass temp.

 

[sftyvlv]

Thanks, for the info. I'm new at metalurgy and I've hardly scratched the surface on the wide variety of topics that relate to this field.
I'm a red seal pipewelder in Ontario,working at a coal fired power station,and am curious to the "hows" and "whys" of welding metallurgy.
I have ASME section IX,II (all of),B31.1 and 31.3 to referance albeit a few years old.
I find this sight most informative and helpfull.
Thanks
Sftyvlv