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Casting is an old metal forming process. Iron liquid is injected into different cavities and forms various casting shapes after being cooled. Heat treatment of castings is a kind of heat treatments of castings. Anneal, normalization, quenching and tempering are widely applied. 

 

The elementary compositions of castings are similar to those of steel. Therefore, all of heat treatments which are used for common carbon steel also can be used for nodular cast iron. However, nodular cast iron contains graphite and graphite and has higher content of carbon and silicon. Distinction also exists in other microelements. So, heat treatment for castings has its own features. 

 

1. Heat treatment can only change matrix structure of metals. But it cannot change shape and distribution of graphite. 

2. Nodular cast iron is a multicomponent alloy, mainly containing iron, carbon and silicon. Eutectoid transformation is processed at a range of temperature. At the range of eutectoid temperature, ferrite, austenite and graphite coexist. And under different temperatures of the range, relative quantity of ferrite and austenite is different. So, different tissues and properties of organisms can be acquired through changing temperature. 

3. Heat can make some of graphite dissolve in austenite. For this, when regulate quantity of graphite dissolving in austenite through changing heating temperature, organisms containing different carbon contents can be acquired after being cooled. 

4. Graphite has poor thermal conductivity and it is difficult for austenite dissolving in it. So, when heat treat nodular cast iron, heating temperature should be higher than that for carbon steel and heat preservation should also be longer.