Yesterday I was making a strut tower bar out of chromoly and had a 20-30 minute argument with an older fabricator as to why I <U>should not</U> clean the surface before welding. (Cleaning the scaling using a 80 grit and paper wheel to scuff the surface). So my question is when you guys weld 4340 together, are you prepping the surface other then brake clean, and exposing the bare metal?

Also what filler rod would you all recommend?

 

I use 80s-2 rod for that. what was his argument towards not cleaning?

 

Well the one valid point he had was that you have to re-finish it after its done (powdercoat, paint etc) and that the welds hold fine if they didnt he'd be dead because of a rollover incident he had in an ATV w/ a cage lol.

But either way I'm pretty meticulous about welding and have a certain process with welding anything. If I'm welding a stainless manifold to a mild head flange (if the flange has surface rust or scaling) i'll usually set the flange in a tub of concrete etch for 30 minutes or so before i weld it

Not only that but people that don't know what they are looking at see a nice header with a couple spots of rust on it and they think its going to fall apart.

 

you don't usually want to use sand paper. it will leave contaminates behind. i use laqor thinner.

 

after it's sanded it's wiped down, I just use an abrasive on metals with scaling on them.

 

I always buff the area with a medium 2" roloc disc before welding chromoly, then wipe with alcohol. That's what has got me the cleanest welds so far.

 

you mean 4130 right?

filler rod:
4130 to 4130 no heat treat, use 80s-d2
with heat treat, use 4130 rod
4130 to mild, use 70s-2

4340 is usually made in stock form and used for shafts and the like.

i take off the dark coating on a deburring wheel then clean with acetone. its nice because it doesnt remove material and doesnt scuff like sandpaper. sandpaper is used when something cant be taken to the wheel. removing the coating also reduces fumes. after welding 4130 for a day without removing the coating, and the ventilation wasnt working my lungs hurt pretty bad for another day.
so remove it and ventilate.
theyre about 40-60$/wheel though, but you can use them on a ton of stuff.