What Is It: Red Oxide(?) Coating for Steel?

Hardened steels (particularly tool steel) will frequently turn red when subjected to the black oxide process. This may be a deliberately enhanced version.
 
Black oxide will turn reddish when applied to case hardened surfaces, especially at higher than normal temperatures. It is an oxide, that's why evaporust removes it.
They did not go to more expense to make it that way, trust me.....that's just the way it turned out and they went with it.
 
Back around the year 2000, give or take a few years, U.S.Steel was experimenting with a finish that came from the chemistry of the steel. It was intended at the time for structural steel but may well have been adapted to other grades.

The finish would self generate, sort of like a thin layer uf rust. Once the surface was thick enough to keep air (oxygen) away, it wouldn't go any deeper. A scratch would corrode again, until it was covered, then stop. I think the idea was to eliminate the need for painting. It could be painted, but for cosmetic purposes only. Sandblasting prior to painting would be a whole different issue.

I do remember the color being a red(dish) brown. I worked in a slab mill where the steel was eventually rolled into sheet stock. So I never got a chance to see or be involved with the process, as it was intended for structural stock. We cast sheet slabs and pipe billets for the petroleum industry. It is quite possible the concept has been adapted to "crucible", or tool, steels or maybe even stolen. U S Steel has an interest in several mills in western Asia.

This is pure speculation on my part but would provide a plausable explanation for the finish.

.
 
We had a big(for us) stadium made from rust stop metal, it was a total fiasco here in Hawaii, sheets of rust would fall off of the girders, it did not work well at all.
 
Last edited:
The steel you're referring to, @Bi11Hudson, is often referred to as weathering steel (or by the trade name COR-TEN).

Pretty slick stuff. I see it used a lot for bridges and high-mast light poles (like next to highways).

I don't think that's what you've got on your tools though, @darkzero. Weathering steel just looks rusty when it builds up it's protective oxide layer, not the nice shade of red you've got.

Could be a similar process, I suppose, but a different oxide.
 
I've seen red-ish & brown colors from poor black oxide processes before. These don't look like that. The red color on these looks intentional.
 
What if it is a dye? I can't second-guess the Chinese, so it's possible they did something different than black oxide. Black dyes are either red-based or blue-based, and the base color shows through until it reaches black. I would fully expect Evaporust and ospho-rust to strip either coating. I'm not sure which solvent would be good to test die vs. oxide with, but I'd probably start with trichloroethylene, which would attack a dye but not an oxide.
 
Aukai said:
We had a big(for us) stadium made from rust stop metal, it was a total fiasco here in Hawaii, sheets of rust would fall off of the girders, it did not work well at all.
Click to expand...
ah, yes, the Aloha Stadium

" There have been numerous discussions with Hawaii lawmakers who are concerned with the physical condition of the stadium. There are several issues regarding rusting of the facility.... Much of the rust is due to building the stadium with weathering steel. It was intended to create a protective patina that would eliminate the need for painting. However, the designers reckoned without Honolulu's ocean-salt laden climate. As a result, the steel has never stopped rusting. "

en.wikipedia.org

Aloha Stadium - Wikipedia

en.wikipedia.org en.wikipedia.org
 
pontiac428 said:
What if it is a dye? I can't second-guess the Chinese, so it's possible they did something different than black oxide. Black dyes are either red-based or blue-based, and the base color shows through until it reaches black. I would fully expect Evaporust and ospho-rust to strip either coating. I'm not sure which solvent would be good to test die vs. oxide with, but I'd probably start with trichloroethylene, which would attack a dye but not an oxide.
Click to expand...

Hmm, possible I think. I don't have any experience with dyes for metal, I have only dyed plastics. Are metal dyes more like a paint or act like an oxide coating? Well aluminum anodizing uses dyes for coloring so I suppose that answers my question.

Trichloroethylene, is that what is used to chlorinate cutting fluids like the old Tap Magic formula? If yes I have the original formula AlumTap which is chlorinated. Not sure how much is in it & would be enough to affect this finish but AlumTap doesn't affect it. Anything else I could try? I don't have trichloroethylene.

I'm sure it's not a paint cause the solvents I tried won't dissolve it, no residue wiping it as if it were a paint. Alcohol, acetone, & brake fluid doesn't affect it. Evaporust is not supposed to remove paint but it does remove this & is why I suspect some type of oxide process. I'd say Evaporust removed it just as fast as cold blue. Well for that one blade I did anyway. Real black oxide takes longer to remove with Evaporust in my experiences.
 
You must log in or register to reply here.
Back
Top