If you intend on painting the metal you will need to clean it.
If it is a large area, you can use a degreaser spray. Acetone on the immediate area to be welded.

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Thank you!
Anxious to get started.

 

Hot rolled steel has mill scale (very hard layer of impurities and oxidization that occurs from the near molten/very reactive metal being exposed to the air). Google mill scale and it is the hard as metal, black baked on looking coating.

Pickled (and oiled) steel will have that mill scale removed via acidic submersion (pickling).

Mill scale is your enemy for welding, as it has a higher melting temp than the steel and will affect your weld. Unfortunately it's hard to grind, but possible. I like ceramic media flap discs/fiber discs, but it can be done with a grinding hard rock wheel and the like.

It will likely come from the steel supplier oily/greasy, which can be cleaned with acetone, alcohol, or any good degreaser.

 

Thank you. I think perhaps Simple green can do the trick of de-greasing. I have tons of acetone and other organic solvents.

 

The internal oil can cause issues, too. The smell. It can boil/off gas and interfere with tig welding. It can also drain/seep after all exterior is clean and welder.

I have soaked stuff in a barrel or pvc drain pipe. There was a ww member who cut a large pvc pipe into a trough, cuts down on volume needed. Mine is just sealed at the end, but be careful because metal will go right through the bottom if it is allowed to slide.

leaving it in the sun will kill the oil, too.

 

what do you mean by internal oils?

 

NON CHLORINATED!!!

just make sure whatever you use to degrease is non chlorinated, as it creates a very harmful gas when heated. cheers

 

Oil that gets inside the interior surface of the steel. For example cutting a steel tube in half and the inside is still coated with oil though the outside is clean.

steel itself does not "absorb" oil", just fyi - And it's a more common question than you think. Oil and sludge can stay inside steel's nooks and crannies though and be very difficult to remove.

 

rarely is internal oil a problem for me on new steel, if it is i dip the end in some alcohol and then follow up with acetone on a cleaner rag/shop towel/paper towel/whatever.

An unprotected steel surface will begin to rust immediately, even if not noticeably it will be oxidizing on the microscopic level. Surface rust and the amount will depend on the time exposed, humidity and dew point changes where the steel is stored. Generally even a few weeks worth is nothing, unless it's soaking in salt water. If your project gets rusty wire brush it away, clean it up as well as you can and use a good rust friendly paint and primer.

 

If the millscale is removed, then depending on humidity and what not, yes the surface will begin to "flash rust", which is very light. If the steel is clean of all oils, but it still has millscale on the surface, then it won't rust as fast, but it will still rust. My two metal supply stores are completely different in this respect. One is actually my LWS, and they store everything outside in the sun, so it has surface rust, but no oil. The other stores everything indoors in a warehouse, so hardly any rust, but your hands will be black after handling anything from there, lol.

These are some coupons I cut up last night, left in the garage to dry, after letting them soak in a light phosphoric acid solution using Kleen Strip Metal Etch

As you can see, little bit of flash rust, but it's nothing a wire/bristle wheel can't take off.

 

that looks nice but arriving at this point ......

 

I used muriatic acid for 12 gauge hot rolled steel in a pvc pipe for 30 minutes and all the mill-scale was completely removed. I tried soaking a 1” plate in the stuff and I barely noticed an effect. I think the 1” plate had a much thicker amount of mill-scale.
I tried phosphoric acid for rust with mill-scale. I cant tell if the mill-scale went away because a black/grey residue was formed from the phosphoric acid. They say the phos displaces the oxygen so you end up with iron phosphate instead of iron oxide ( rust). The next claim is that this iron phosphate is both weldable and paintable, unlike rust. Is that true? Or do I need to grind that stuff off where I will weld?
I read that phosphoric acid is not good at removing mill-scale. So some people will let new hot rolled steel sit outside to rust away the mill-scale and then use phosphoric acid to remove the rust. Does anybody do that?


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Wow muriatic acid is dilute HCl , I think. Nasty stuff. Reactive with metals. Once the metal is in contact with the strong acid, it must be neutralized or rinsed off... more steps... what to do. Not into having to conduct metallurgy experiments to weld.... always somehing for a newby.