The heat treatment most frequently applied to gray iron,with the possible exception of stress relieving,is annealing. Annealing of gray iron consists of heating the iron to a temperature high enough to soften it,and/or to minimize or eliminate massive eutectic carbides, thus improving its machinability. This heat treatment reduces mechanical properties substantlally, however,it will reduce the grade level approximately to the next lower grade.

　　Gray iron commonly is subjected to one of three annealing treatments,each of which involves heating to a different range of temperature. These treatments are ferritizing annealing, medium(or full)annealing and graphitizing annealing .