Welding Chromoly to Mild Steel

[Buzz]

I am restoring and upgrading a 60's Front engine Dragster frame. I was wondering if it is possible to TIG weld Chromoly to Mild Steel without running into stress or any other problems. The portion to be TIG welded will be the front MS tubes inserted into the Chromoly frame tubes.

[Paul Seaman]

Buzz: haven't forgotten ya my partner hasn't called back with the answer this is his specialty. In a word yes it can be done but the particulars is what I called for help with filler, gas mix, amperage, whatever. He does alot with cromoly and mild, dirt racecars chassis cromoly and sub-structures mild so they bend and take up energy. I'll let ya know later, maybe the weekend before I hear.

[Rob]

Buzz,

Sounds like a fun rebuild! No problem mating mild and CM tubing, as long as each is sized correctly and the joint is designed properly. If it's an insert joint (one tube slid inside the other), cut the outer tube at an angle (30-40 deg). Be sure any existing tubing meets your sanctioning body's reg's and that it is free of significant corrosion, expecially on the inside. Also inspect the existing tubing for fatigue cracks.

I typically use ER70S-2 filler for mild/CM joints. The only gas I use to tig is 100% Argon.

As you can see, this is a pretty typical mild and low alloy set-up. You've probably done most if not all the above, if you run into specific questions, just post.

Hope this helps.
Rob

[ASKANDY]

Buzz,

If you are looking for a little more strength, the ER80S-D2 is a great filler. In any case, try to keep your arc length low and don't overheat the joint. Chrome moly is sensative to too much heat. You may wish to stress relieve the joint after welding. Take a 900deg temp marker and mark about 3/4 to 1 inch from the joint and use a torch with a neutral flame around the welded area. About 1100deg is good for tubing applications. Make sure to keep the torch moving to avoid hot spotting.

Hope this helps.

andy

[Paul Seaman]

Buzz turns out rob is dead on Er70s-2 and argon and keep the heat to a minamum with short arc. good luck

[Blondie_486]

Buzz,

I would strongly recommend stress relieving as Andy stated! Also don't let it cool too quickly either.

Blondie_486

[Buzz]

Thanks for the replies guys. On the same lines, I did a spark test on the tubing in question plus using a piece of Chromoly scrap as a reference. The sparks from the tubing on the dragster and the scrap appeared to be the same. Is there another way of telling the difference?