I recently read someone asking for a "brine recipe" for hardening mild ie 1018 or a36.
we call it superquench in the smithing world
heres the recipe

4.5 (ish) gal of water
1 lb bag of salt
1 reg sized bottle of Dawn dish soap
1 lil bottle of jet dry
mix em all up.
i recommend the salt first
the principle behind this stuff is as follows
the salt raises the boiling point
the dishsoap cuts down on cavitation and water jacketing
the jet dry breaks surface tension down a tad
great stuff, but get a lid, it can be messy