welding Mild steel to Chromemolly roll cage

[FABMAN]

Got a question for you all.
My buddy has a race car that's an older build and we are adding some extra bracing to the roll cage with mild steel 1-5/8 tubing. We are pretty sure the cage is also mild steel, but if it were chromolly, would there any trouble in MIG welding the mild steel bracing to the chromolly, any special procedures before welding ? I have a millermatic 211 with 70s-6 .035 wire, would that be suffice ?
And any tips on how we can tell if the original cage is mild steel or chromolly ?
thanks for any help you guys can provide.

[OscarJr]

I'm no expert, but just about the only thing I would do is make sure the shop ambient temperature was at least 70°F. I would also make sure there are zero drafts that would aid in increasing the cooling rate of the joint.

Many chromoly tubes are labeled just that "4130 Chromoly-N", for those that are in the normalized condition. Is the cage painted?

[ryanjones2150]

If you're worried about it cooling too fast, just hit it with a torch before and after. I've welded plenty of 4130 to mild steel for drag car stuff. I'm not really the expert or anything, especially since we use whatever we can get our hands on to build the garbage we race and we're "roadkill approved" I might add. Ask Freiburger about it, he'll vouch for me. <br />
<br />
But, if you really are concerned about it, give it some preheat and tig it with er80sd2, which is my process of choice for roll cages. But if it was me, I'd probably just roll with what I had.

[FABMAN]

Thanks guys.. after looking at some pics of the installed roll bar, the welded joints are definitely mig welded and we are now 99% sure the cage is mild steel, so the supports we're adding which are also mild steel will get mig welded.. wish i could get my tig machine to his shop, but mig it is.. thanks again

[Michael ray]

Roll cage??? I Got a 46 willys jeep with just a rusty windshield frame and a boosted lt4 and t56. Looks like I gotta get on board with one of those...probably going to weld 4130 directly to my frame...got pIles of 4130 and been welding to mild for long time on many projects...only 1 failure but thats a whole different story... i weld about as good as I drive if that means anything

[ryanjones2150]

Well, are you a good driver?

[Michael ray]

See me standing in my old zookie...good enough for most maneuvers but have the occasional back fire from time to time

[Michael ray]

Quite often to be honest...

[racerx]

Not meaning to hi-jack this thread,but sense were on this subject of molly/mild steel.I need to weld a molly steering joint to a mil steel shaft.What gas/wire will this require?...........Thaxs

[Michael ray]

If it's steering I'd probably tig with pre and post heat..I do mig it all the time but on less important systems than steering. No problem with mig, I use 030 and 035 wire mostly. As for gas I just use 75 25 mix on the mig...pure argon on tig.
Shaft from column to box/rack or from unit to wheel knuckle? Forces are much lower on the column shaft so I wouldn't be afraid either way

[ryanjones2150]

Don't sweat it, not nearly as life changing as it sounds. Chromoly and mild steel are successfully welded all the time. The smaller the pieces, the less likely you'll need any pre or post heat. I'd say tig it for sure and take your time. The reason for pre and post heat is so it doesn't cool too rapidly. If the parts are small, it will most likely heat up the rest of the part away from the weldment that it won't be an issue. You can use whatever mild steel tig wire you have and pure argon. I have never migged chromoly to mild steel, but I'd imagine it's the same deal for that, normal mild steel wire and the appropriate gas for that wire.

[racerx]

Thaxs fellas got to refill the bottles tomorrow and get some wire from the supply store anyway, I have the small bottle for argon think i'm going to get a bigger bottle that little bottle does not last long.........Thaxs

[racerx]

Don't sweat it, not nearly as life changing as it sounds. Chromoly and mild steel are successfully welded all the time. The smaller the pieces, the less likely you'll need any pre or post heat. I'd say tig it for sure and take your time. The reason for pre and post heat is so it doesn't cool too rapidly. If the parts are small, it will most likely heat up the rest of the part away from the weldment that it won't be an issue. You can use whatever mild steel tig wire you have and pure argon. I have never migged chromoly to mild steel, but I'd imagine it's the same deal for that, normal mild steel wire and the appropriate gas for that wire.

I have actually flux core some molly/ms before(it's all I had at the time)and it held up fine.As a matter of fact this is the joint that's getting cut off and re-welded due to the new rack system being installed.

[ryanjones2150]

Kind of figured there wouldn't be much difference.

[Michael ray]

Tig it real nice then melt some brazing rod on it and tell your buddies you brazed it...see how many are willing to ride with you.