"回火过程" can be translated as "tempering process" in English.
Here, "回火" refers to the heat treatment process in metallurgy where a previously hardened metal is reheated to a specific temperature below its critical point, held there for a certain period, and then cooled, usually in air, to reduce brittleness and increase toughness. "过程" simply means "process." So, combining them gives "tempering process."