"Peter Grey" wrote in message
nk.net...
The oxide doesn't change back to steel.

Correct. It fumes off.

Whaaa?! You do realize ferrous oxide has a *melting point* in excess of
2,000°F, don't you?

That explains why the color disappears as the temerature of the piece
goes up.

Maybe under heavy reduction, where the hydrogen and, more importantly,
carbon in the flame are able to actively reduce the oxide from FeO to Fe
(such happens readily with copper metal), but not under any other
circumstances.

Tim

--
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