Post deleted by grape creek

What is the condition of the tube to start with ? What rod are you going to weld with ? In any case I would temper after welding.

There are surely some "Homebuilt Aircraft" sites on the web that could answer this.

I would be scared of hot bending and welding without getting into hydrogen embrittlement.

What welding process are you planning on using?

Grape Creek,

4130 steel has about the highest carbon level I would recommend for a novice to weld. If you bend the rod, you must consult forming tables so you can get a free bend without kinking. There is more flexibility if you do this hot or in a restricted mandrel.

Before welding, select a low carbon weld electode or weld wire. Almost, recommend a skilled welder due to the effects of buildin notches you can introduce through welding flaws. Remember, your welded structure must endure impact loading and low cycle fatique in a cold environment.

When welding, I would guess the 4130 tube or rod would have to held in a fixture to allievate weld cracking. Immediatley following welding, cool slowly or even reheat to allievate residual stresses.

Now, you should know the hardness (strength level) of the original tube so a proper temper or stress relieving temperature can be assigned. If a high level of strength and toughness is required, then austenitize, oil quench, and temper the entire structure.

What I have listed is just a few rudimentary basics for you to to inquire about this with someone familiar with welding and metallurgical procedures up there.

Good luck!

Dak