8670 is very easy to work with and it is forgiving in heat treatment. It has very good toughness as well. My recommended heat treatment is 1500°F for 10 minutes, quench in fast or medium oil, and temper between 300 and 450°F depending on the desired hardness. This article also has recommended forging, annealing, and normalizing temperatures and some guidance on heat treatments to avoid such as underaustenitizing or overaustenitizing.
One of Dr. Larrin’s more technical pieces.View Linked Article