Stress Relieving

Internal stress in cast material is very common because every casting undergoes cooling which is non-uniform. After certain time period has passed, these internal stresses tend to be relieved almost spontaneously. Such self-relieving of stresses may cause changes in dimensions which may not be permitted for working of parts of machine. Therefore, it is imperative that cast material (parts) must be stress relieved before bringing such parts in service. Cast iron is stress relieved by heating it to a temperature in the range of 400-500oC and kept at this temperature for a few hours. The cooling is done slowly or as per the rate for a particular structure. Stress relieving of cast iron is referred to as seasoning of casting.