Ed Huntress wrote:

The next step down is flame-hardened gears. These are made from
high-carbon steel, or a quick-quenching high carbon alloy. This flame
hardening requires a fixture and a quenching system that surrounds the
gear all at once -- a spray-type or an agitated oil bath.

So spin the gear on a mandrel with just the teeth in the O/A flame until
red hot and then quench it in some carbon rich used diesel oil?