Hi George: There's a technique called 'bluing" http://en.wikipedia.org/wiki/Bluing_(steel) which is a controlled rusting process designed to protect against further rusting. Not sure if it's going to give you the kind of rust you want but FYI. John

I could be wrong, but it sounds as though there might be some pitting corrosion going on. If it's possible, I would try polishing the surface after your other preparation steps (it could be that scratches / defects caused by the abrasion with steel wool are initiating some pitting). If it is pitting, then polishing should reduce this.

I recommend to put the (degreased) part into a acidic solution of NaCl (10 %) in HCl (10%) for some minutes of course not as long as you see "bubbles of H2" :-)..) not too long , then take it out and rinse with water; let it sit for some days preferably in humid air :-)

Halides are catalysts for ferrous oxidation so they attack Fe°. Problem with manganese carbon steel is that it comes from a melt with a differential cooling effect: Outermost quenches first and foremost, Innards have greater growth of graphite, etc. Quenched surfaces are more uniform but quality is arbitrary and depends on processing conditions. The more you etch/rust the more inhomogeneities expose and differential oxidation. If you want a thin rusted surface, grit blast to requisite surface profile and just use peroxide coat and let dry. No halides, as they screw displace to make the surface micro-rough. In any event of chemical treatment when sufficient rust accumulates blast with deionized or distilled water, then blow dry with hot, dry air. Just depends on desired thickness and surface r.a. One really needs to know the final purpose of the film.

Same as you are doing but before immersion, spread uniformly over the surface some noble metal powder like Ni, Cu or Pt. Chek your half cell potentials depending on the ammount of rust you want.

Treat the surface with H3PO4, it will provide you with nice primer. Not is that the protection is absolute, but its is cheap, and somewhat helps.

Not sure how large this piece of CS you need to rust is and how thick of an oxide layer you need but a very controlled and uniform way to oxidize the surface of solids is to use oxygen plasma oxidation/cleaning. If you have access to such a device at your institution you should be able very controllably (i.e., down to molecular level) and consistently oxidize the surface exposed to the plasma cloud in the generating chamber. This will also remove by oxidation any organics that may have accumulated or been deposited onto the surface and so really no precleaning other than make sure free of dust and large debris is really necessary. Oxide/rust layer growth should be faster than simply leaving in open air but still may be slow and the device you use may have a maximum allowable time of continuous run due to overheating. You should also make sure depending on the type of plasma cleaner you have available to use that it is actually safe to place such a metal into it. If you can get access to this maybe check out the following reference (you can probably find others as well):

Plasma cleaning of metal surfaces; 0. F. OKane and K. L Mittal; Journal of Vacuum Science and Technology 1974, 11, 567-569

Hai George,

best way to get uniform corrosion film on carbon steel can be done by hydrothermal method. since the source for corrosion film is metal ( carbon steel ) itself. keep your specimens (1040 carbon steel) in static autoclave with water chemistry condition like alkaline solution with NaOH/NH3, with low dissolved oxygen by hydrazine. place the autoclave with specimens at 200-250C ( 4-8h) for getting corrosion film. one should expect a micron thick film on metal surfaces.

Hi George,

To answer to your question, it depends of which rust you want on your steel. Is it Lepdicrocite, Goethite, Magnetite, Maghemite, Hematite, Ferric Green Rust, Akaganeite, Ferrihydrite, Ferroxyhite, ....? What is the rust thickness do you need?

You can form the rust you want by polarization in an appropriate solution and with the appropriate potential or current.

Folks, I personally treat metal surfaces with 1 mole/L H3PO4. Metal Phosphate protection layer appears on the surface. That is CHEAP, no harm is done.