[buildsjets]

For reference, here is a ring which is believed to have come from China's Long March BuNo Y77. Note the similar scale, and similar discoloration. https://spacenews.com/india-examining-crashed-space-debris-s...

I design and build all sorts of hardware relating to air-breathing (jet) propulsion, including gears. I agree with mkl. Those are not gear teeth. They have flat flanks, and no involute profile. No one makes gears with a gigantic U shaped root. They appear to me to most likely be clearance slots, to go around protruding bolt heads on a mating part. I have designed similar counterbore features myself.

What makes you claim that this part is steel? The article does not say that. Is that a fact, or are you guessing?

[mkl]

The appearance of rust on the surface of the article's main photo suggests steel. I guess heat from reentry may lead to that appearance on other materials?

[buildsjets]

Inconel looks just like that after exposure to heat, and is much more likely to have been used to build an aerospace vehicle than carbon steel. Most jet aircraft exhaust systems are made of Inconel and oxidize to a dull brown at 1200F or so. Like on this 737NG:

https://aviation.stackexchange.com/questions/90974/what-are-...

The exhausts that turn iridescent purple for a while due to heat are titanium, for example this 787. So I would suspect the debris is not titanium based on lack of heat marking.

https://www.reddit.com/r/aviation/comments/b77f5x/b787_its_s...

So if I were to guess what kind of metal it was solely based on coloration and suspected use case, I’d say Inconel.

But I wouldn’t make a guess at all, because it’s naive to assume that you can identify a type of metal based on a grainy freeze-frame of a cell phone video that has been re-encoded an unknown number of times before publication.