4130 Procedure & Filler Material

[CRG]

I own a 1946 Republic RC-3 that had a filet weld failure on the landing gear torque tube assembly. In 1961 there was a manufacturer’s Service News letter that stated if the weld was cracked to:

grind off all existing weld down to parent metal and arc weld with nickel steel rod, building up the bead around the fitting

There was never an AD issued regarding this problem and the above quote is all the information given in the Service letter regarding repairs: No filler material specified, no preheat, no stress relieve procedure, etc., just the vague reference to nickel steel rod. Looking at the broken pieces (¼” plate actuation arm welded perpendicular to a 3” tube with a fillet weld), it is obvious that the problem with the existing weld was the joint design and incomplete penetration. The weld method the factory employed was SMAW.

ER80S-D2 would seem to be a reasonable filler material for the 4130 base metal for GTAW or GMAW; however, it is not a nickel steel material as vaguely described in the manufacture’s Service News letter. This aircraft is not supported by the manufacturer and because it was only made in 1946 & 1947 there are only a small number of them around. Hence, limited used parts and very few people experienced with the model can be found.

What filler specific filler material could the Service News letter be describing? What is the advantage / disadvantage of SMAW verses GTAW for this type of weldment (length of weld is 1.5”). How can I find a welding procedure that is appropriate for the application?

 

[metengr]

I would guess that that the filler metal was either E80XX -C1 or C2 or M or an E90XX-C5 or M. The nickel containing low alloy steel weld rod results in a tougher and more ductile weld deposit that can better absorb shrinkage/thermal stresses during welding. It is very forgiving to work with.

If I were going to make this fillet weld today, I would probably use a local preheat of 400 deg F with a maximum interpass temperature of 650 deg F. I would probably select the GTAW (TIG) process over the SMAW process for the main advantage of grain refinement in the base metal heat affected zone in the 4130 tube and base plate for increased toughness, and to reduce susceptibility to hydrogen cracking. Use tight stringer beads to complete the weld joint. To improve the weld joint design over a simple fillet weld, I would bevel the 3" tube end to provide a full penetration strength weld with a 1/4" external fillet to the actuator arm base plate.


As far as filler metal selection, a closer match to what was originally specified would be an SFA 5.28 ER80S-Ni1 for the GTAW process. After the welding is completed, I would perform a post weld bake at 550 deg F for 2 hours, slow cool to ambient temperature, and have a nondestructive test performed to assure acceptable weld quality.