There’re some suppliers that don’t stress relieve grey iron castings, and there are some that do. The advantages of stress relieving castings: various cooling rates in various castings after they are released out of the mould (owing to complex geometry with different thicknesses, geometry curvatures/surface, thin sections, etc).

After a period of time—usually from several months to a year—castings left on their own will relax and stress will start to dissipate. In this relaxation period, the dimensions and the geometry of the casting will move steadily and finally stabilize. All said and done, it’s not recommended to cast and season, though it was the most widely used method with large castings decades ago. Thus its significance. This is particularly critical if machining operations need post-casting, usually with tolerances of sub-thousands (of an inch) in relational dimensions between the features.

It isn’t beyond our understanding that a casting that hasn’t been stress-relieved can satisfy all dimensional requirements at the industrial unit, and over time (while sitting on the shelf, transportation) can shift away from specifications. Therefore, stress relieving is a key process for all castings for maintaining dimensional stability over its useful life.

There are different options available for stress-relieving, including thermal stress relieving, ranging from small to medium-sized castings.

Usually, the best time to stress relieve is post-machining and just before final machining. There are times when cost considerations and logistical issues may tempt one to go about stress relieving raw castings and then carry out machining operations without any treatment. Nevertheless, machining operations can induce changing degrees of stresses into the part. When stress relieved immediately before final machining, both machining stresses as well as casting stresses can be removed to realize the best possible results. If casting demands precision requirements, it may be required to perform stress relieving two times, once when the casting is removed from the mould and then following rough machining.