A friend used to do this.
He had 2 propane fired tanks, one hot water, one solution.
Bluing ran about 320F, so lots of steam and humidity.
Also fairly dangerous if not careful.
Heat de-greased parts in hot water
Shake off ALL water
In hot tank till blue
Rinse in hot water
Dry, and oil
Sorta like that.....


Dumb, but learning...Prof Em, BSc(ME), CAE (FYI)