anything to know about welding chromoly tube?

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I'm looking to build a motorcycle frame in chromoly.It will be a trellis frame, something like this:

that's just a quick photoshop to give a rough idea. I've built frames in 1018 before, but not in chromoly. Is there anything special to know/do when welding chromoly as opposed to mild steel? What would be best choice for filler rod? Is argon sufficient or will I need a different gas/mix? Will I need to heat treat the frame after welding to relive welding stresses?It will be tacked with MIG and finish welded with TIG.Any links or references that may help me out?Or should I just stick to 1018 that I have more experience with?Cheers.Last edited by gr8twhite; 3 Days Ago at 07:43 PM.
Reply:I bought a bunch of various filler a while back and 4130 was labeled chrom- moly I think it needs post heat treatment???I could be wrong Ive used it for mild steel welding and it held up fine.Miller 211Hypertherm PM 451961 Lincoln Idealarc 250HTP 221  True Wisdom only comes from Pain.
Reply:They use in aircraft a lot of chromoly tubing and welding with torch.The only tubing I use is EMT and that I brazing the mid steel tubing. Dave

Originally Posted by gr8twhite

I'm looking to build a motorcycle frame in chromoly.It will be a trellis frame, something like this:

that's just a quick photoshop to give a rough idea. I've built frames in 1018 before, but not in chromoly. Is there anything special to know/do when welding chromoly as opposed to mild steel? What would be best choice for filler rod? Is argon sufficient or will I need a different gas/mix? Will I need to heat treat the frame after welding to relive welding stresses?It will be tacked with MIG and finish welded with TIG.Any links or references that may help me out?Or should I just stick to 1018 that I have more experience with?Cheers.
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Originally Posted by John T

I bought a bunch of various filler a while back and 4130 was labeled chrom- moly I think it needs post heat treatment???I could be wrong I've used it for mild steel welding and it held up fine.
Reply:I think Er80 is the better match for 4130 non hardened weldments. In fact the only filler AWS will offer a SWPS for 4130 is Er80S-B2. But ER80s-D2 is more common and easy to use. ER70 was recommended for non heat treated weldments until Er80 was formulated. Basically they added some 4130 to the Er70 to achieve a better match without a great deal of base metal dilution. If you are going to heat treat your weldment then you must use 4130 filler. Only advise though is make sure you have a good cup size and lengthy post flow and when terminating the arc keep the rod and puddle in the gas stream. Otherwise the weld and rod end will contaminate and bubble up horribly upon restart. Then is is hard to get rid of the foaming without grinding out the puddle or using stainless. And if you do think you fried the rod end clip it off. You will find out eventually but beware. Actually 4130 is a joy to weld. Clean and the puddle is not watery. The filler is nice and stiff and goes where you put it. If your wall thickness is 1/8" or less no prehieat or stress relief is required. More than that preheat and post weld stress relief is recommended.Weld like a "WELDOR", not a wel-"DERR"

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Reply:Enjoyed the videos. Thank y’all for this threadRetired Old GuyHobart 210Lincoln AC/DC 225/125 Tombstone Evolution 14” Saw
Reply:Its probably a fact there is a lot to know about it, how much it all matters I bet has a lot of opinion,  Seen a lot of dirt bike stuff welded up fugly with 6011 that actually worked as long as the factory stuff. OA too.  Wire feed even better.www.urkafarms.com