Whats stronger: a bend or a weld?

[Ender]

Just for explaination's sake, material in question is 1.500"x0.375" mild steel bar. I want to put two opposing 90* angles in the piece. Would a bend be stronger, or would cutting the pieces and properly welding them at 90* be stronger. Just curious.

Where I'm at right now, I don't have the equipment to bend the piece (no O/A setup) so I was planning on making three horizontal cuts about half way into the depth of the piece on the side opposite the bend, allowing it to sort of fold, and then welding up both sides for good measure. Is this a no-no? Is this acceptable. Piece is not a structural element, but I'd really it rather not break and be whichever of the two options is the strongest.

Thanks,
Ender

[WelderBoy]

Depends on the steel and how well the weld is placed. A weld would be stronger, but the HAZ surrounding the weld would be the weak point.

Most engineers only allow one bend on a piece of reinforcing bar because it reduces it's strength so much. But they never allow welding on it in my experience, so a bend may be better if done properly.

[MoonRise]

It depends.

It depends on the properties of the steel, the bent steel, and the welded steel.

In your case, with mild steel 3/8 thick, I'd say to cleanly cut it and then weld it. Skip the partial cuts. Weld it from both sides and get full penetration and do a good welding job and the welds should be stronger than the original material.

[e_racer1999]

i would say it also depends on what forces are placed on the final product.... l

[tanglediver]

Bending flat stock is usually fine, because the grain in the metal usually runs the length of the piece. When you start bending cut peices of plate it becomes important to bend at right angles to the grain.

[David R]

Cut and welded inside corner and out side corner will be strongest.

MY opinion, I aint no engeneeer.

David

[riley mcmillan]

If the material is cold rolled flat bar (1018), it will break if you bend it. Hot rolled flat bar (A36) will bend nicely. I would't use anything less than a 1/2 inch inside radius. I don't really know which would be stronger but I think David R is correct on that.

[pulser]

I just finished doing alot of thinking and typing on this question, and then lost the response when I hit the submit button and had to re-login again, what a pita!

So, something to think about, what kind of strength are you talking about, ultimate tensile, yield, fatigue, fracture toughness, impact strength, wear resistance, etc.? How it is welded or bent can improve and/or degrade the various strength properties.

My guess is that a properly done cold bend would have overall better properties in most strength categories than a properly done weld. Assuming there are no weld defects like voids or undercut, the welded piece will still have a large microstructure and strength transition from the base metal, through a coarse grain/"weakened" HAZ, to a higher strength weld metal. The cold bend should have less of differential in microstructure and strength between the base metal and the strengthened "work hardened" bend area.

[TSOR]

Originally Posted by pulser

I just finished doing alot of thinking and typing on this question, and then lost the response when I hit the submit button and had to re-login again, what a pita!

That happens a lot! I've learned to highlight and copy my responses before I hit submit. That way, if it gets lost, I can just hit edit/paste and try again.

[Supe]

If you're only looking at strength, then a weld will be stronger than a bend in mild steel assuming the electrode has a higher tensile strength than the base metal.

[pulser]

Yep the weld is stronger, but what about the HAZ?

The bend is also stronger than the base metal, it is work hardened.

[Joe H]

I think that if you want a sharp 90* bend, a weld would be better. A bend would be ok for a bigger radius. This is an observation from experience, with no data to back it up though.

[Seven Gables]

Originally Posted by Joe H

I think that if you want a sharp 90* bend, a weld would be better. A bend would be ok for a bigger radius. This is an observation from experience, with no data to back it up though.

Yes. For a sharp bend Fully cut it and weld it. For a properly radiused bend, 3t to 4t, it would not matter as the material strength would be the weak point.

Originally Posted by WelderBoy

...Most engineers only allow one bend on a piece of reinforcing bar because it reduces it's strength so much. But they never allow welding on it in my experience, so a bend may be better if done properly.

Reinforcing bar can be bent as many times as required; stirrups for example have from 2 to 5 bends. But, you can not heat bend any reinforcing. Only cold bending to the proper inside radius is permitted. This will not appreciably affect the strength of the bar. The current design procedures take this slight reduction into account in the design.

Welding can be performed on A706 reinforcing bar; not on A615, standard reinforcing bar. This is due to the fact that the A706 chemical composition is designed to permit welding. A615 will be weakened substantially by heat bending or welding. It is possible to break a #11 bar by hand that has been heat bent.

Derek