Welding 50ksi Structural to Q&T Plate

[cnuk]

I am trying to redesign an existing piece of outdoor structural equipment and bring it in line with code. I have two options to rework a deficiency where a square HSS member joins to a plate with a fillet weld around the square HSS:

1. Replace an 1 1/4" A36 plate with a ~80 ksi plate. Likely will have to a quenched and tempered plate to get that strength.

Q: How difficult is it to weld a 50ksi plain carbon structural steel to a 80+ ksi Q&T plate? I suspect a detailed weld procedure (preheat, rod selection, etc) will be required.

2. Upgrade to a 50ksi plate but it will still be plain carbon steel. To get the increased strength add gussets/braces where required. Can continue to use the existing 7018 rods we are currently using. Will be heavier but "simpler" and maybe more cost effective in the end.

I suspect most will pick option 2 as the preferred option.

 

[metengr]

Q: How difficult is it to weld a 50ksi plain carbon structural steel to a 80+ ksi Q&T plate? I suspect a detailed weld procedure (preheat, rod selection, etc) will be required.

It is not difficult to weld carbon steel (A 36) to a low alloy quenched and tempered steel plate, certain precautions are required. Preheat will need to be reduced to 150 deg F or less, and the interpass temeprature would need to remain at or below 350 deg F (this is critical). Because you are dealing with a base material that has been heat treated by quenching and tempering, post weld heat treatment should not be performed.

I would suggest a E9018M filler metal if you are using the SMAW process. This filler metal is typically used for welding ASTM A 514 low alloy steel plate that is quenched and tempered to itself or to a lesser grade carbon steel.

I would strongly suggest you qualify a welding procedure for this base material combination.

item 2; yes.

 

[cnuk]

Thank you for the help by sharing your knowledge. Very helpful.

 

[HgTX]

I suppose it's hard to get A 709 HPS 70W in small quantities, but it's considered to be about as weldable as A 572 Gr. 50 steel if you can get your hands on some. Welding it to the Gr. 50, you'd use the same electrode you always use, but you'd need to use some preheat.

Hg

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