Heat treatment ofcast can’t change the shape of the graphite and harm of removing flake graphite，heat treatment of only used in removing casting stress of casting.
Aging treatment of gray iron cast:
Complex shaped castings emerge inner stress in the progress of casting ,due to wall thickness of each part is asymmetrical，make the castings be variant. Purpose of aging treatment is to eliminate this casting stress. Aging treatment is divided into natural aging and artificial aging . Natural aging is to put castings outdoors for several months , half a year or long time make the castings be out of shape relaxedly. Eliminate casting stress gradually. But this method long production period，casting stress can’t be eliminated incompletely，artificial aging is low temperature annealing ，Heat the castings to 520-550℃ with slower rate of temperature increase.
Graphitizing annealing of gray iron cast
When cool down the castings , due to the speed of cooling is more quick，the surface or cross-section is easy to appear chilling tissue，which make the hardness and brittleness of casting increase.
The passage above talks about parts of heat treatment of gray iron cast. This is for your reference only.