Editing Metal casting (section)

===Cooling curves===
[[Image:Dendrite formation.gif|thumb|300px|Intermediate cooling rates from melt result in a dendritic microstructure. Primary and secondary dendrites can be seen in this image.]]
{{See also|Cooling curves}}

Cooling curves are important in controlling the quality of a casting. The most important part of the cooling curve is the ''cooling rate'' which affects the microstructure and properties. Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure. Below is an example cooling curve of a pure metal or [[eutectic]] alloy, with defining terminology.<ref>{{Harvnb|Degarmo|Black|Kohser|2003|pp=280–281}}</ref>

[[File:Cooling curve pure metal.svg|class=skin-invert-image|500px]]

Note that before the thermal arrest the material is a liquid and after it the material is a solid; during the thermal arrest the material is converting from a liquid to a solid. Also, note that the greater the superheat the more time there is for the liquid material to flow into intricate details.<ref>{{Harvnb|Degarmo|Black|Kohser|2003|p=281}}</ref>

The above cooling curve depicts a basic situation with a pure metal, however, most castings are of alloys, which have a cooling curve shaped as shown below.

[[File:Cooling curve alloy.svg|class=skin-invert-image|900px]]

Note that there is no longer a thermal arrest, instead there is a freezing range. The freezing range corresponds directly to the liquidus and solidus found on the [[phase diagram]] for the specific alloy.