Thread: Gas forge for heat treating?

Originally Posted by jfk742

Also have watched your video on recalescence. So the darker area is boundary between perlite and martensite?

Pearlite and austenite. The transition from ferrite/pearlite to austenite is endothermic and the transition from austenite to ferrite/pearlite is exothermic. Pearlite is a layered structure of ferrite and cementite, hence the ferrite/pearlite. Martensite forms when austenite is cooled below the martensite start temperature ~425 F or so.