Aircraft 4130 Chromemoly Welding

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Dr. Majic and Dr. Young recommend RG45 for welding of 4130 tubes.  Dr. Young also likes coathangers.

For fun, I butt welded 4130 coupons together with coathanger (RG Black) and subjected them to the big hammer bend test. It passed. I never use them for serious work.

I keep 5 types of steel rod in my shop and I periodically round robin test them. For O/A I keep coming back to RG45. It fillets very nicely, doesn't spatter at you, and it is a deep penetrating rod compared to RG60. The tensile strength difference is compensated by:
  1. We don't grind weld beads (with rare exceptions, like where a bolt/nut needs a flat) so the bead is always thicker than the parent metal.

  2. Proper joint design for aircraft should never put a weld in pure tension. At least 50% of the load is carried in shear.  If we were pipefitters I would have a different opinion. As part of the cert process, the test coupons cut from your joint are ground/sanded flat, then tested in tension. RG45 might well fail the test on high strength steel pipe.

Lots of salesman push the E-rods for gas welding. That's a poor recommendation as the chemistry isn't right for gas welding. Too much sparking, spattering, and a nasty tendency to crater the end of the bead.

Dr. Joseph Maj 
The Dow Chemical Company
Analytical Sciences Laboratory

(Kent's note: Dr. Maj very kindly participated in our 5 hr. Instructional video on Aircraft Chromemoly .

He has been teaching at Osh for many years, and welds a very fine tubing cluster. "Dr." Young is Joe "The Polish Ace" Young, a veteran torch welder of 50 years' experience, and a veteran instructor at Osh.)