Welding CDS, T45, chromoloy etc.

[offroad 68]

Looking to build another buggy like the one I race but with some improvements, would like to make the space frame lighter than my current one thats made from 3.2mm steam tube so thinking of using Cold drawn seamless or T45 or even chromoloy/ renolds type tube but a massive worry for me is getting cracks in the welded areas, I read on the internet about pre heating or heat treating areas but there are so many conflicting opinions I do not know what to think.
Does any one know for deffonate having had first hand experiance of working with these kinds of materials?
Thanks Lee.

 

[''Left a Bit'']

Get the area clean to start with, and don't put too much heat into the tube (i.e, if you don't get the weld quite right, you're better off putting a new piece of tube in if you can, rather than grinding it off and re-welding), the weld itself should be ductile if you're just using normal ER70 wire in a MIG or similar (and you'll have a fillet weld on the tube which is much thicker than the tube itself, so you don't need a high strength weld material, or heat treating, the material isn't thick enough to warrant it), but the area directly outside it will harden a little from the rapid cooling, so if you have to re-do a weld it just gets harder and harder and you end up with a stress concentration that snaps the tube just outside the weld itself.

Tbh, if you're any good with a MIG/TIG you should be fine just cleaning up and welding as usual, you're better off making one pass with the TIG rather than a root and capping pass, obviously.
If you're not quite happy with the heat you've put in on something that you can't really replace, a thin plate gusset welded in a couple of inches either side of a tube corner/meeting will take some of the stress outside the main HAZ area.

You're better of with T45 rather than 4140 chromoly either way, it's not effected by welding heat quite as much.

 

[offroad 68]

Bit of a catch 22 then, not enough heat/power no penitration too much could crack :-\ so if I had built a chassis from 3.2mm blue band steam tube with no problems what thickness could I get away with building it out of in (same od)t45.

PS are you at the NORC event sunday left a bit?

 

[''Left a Bit'']

Bit of a catch 22 then, not enough heat/power no penitration too much could crack :-\ so if I had built a chassis from 3.2mm blue band steam tube with no problems what thickness could I get away with building it out of in (same od)t45.

PS are you at the NORC event sunday left a bit?

Not sure, I'm going past so I'll call in if I have time, but we've some repair work on our buggy to sort out, Kirton battered the underfloor to death (there's a couple of holes punched clean through the skid pans), engine cage is bent, and a rock put the windscreen through...

T45 sizes are restricted by the MSA cage sizes/thickness obviously, but I would have no qualms at all going with 2mm thick main hoops/structures in T45