- Stress relieving is intended to reduce/stabilise residual stresses, either inherent in the base materials or induced by prior manufacturing processes such as casting, machining, cold work and welding.
- It is normally restricted to relatively low temperatures and carried out to keep changes in material structures and mechanical properties to a minimum.
- Stress relieving is normally carried out after rough machining but before final finishing (machining or grinding).
- Conventional stress relieving applied to carbon/low alloy steels and cast iron is typically carried out between 500°C and 680°C.
- Stress Relieving can be applied to almost any metal. Choice of temperatures and time needs to be appropriate to the material being treated.
- Stress Relieving is carried out so as to produce minimal changes in material structures or mechanical properties.
- Without stress relief, subsequent processing may give rise to unacceptable distortion, cracking and associated service problems.
- Stress relieving can aid substantially in subsequent machining and forming, reduce the risk of instability problems in service and aid in subsequent heat treatment processes such as carburising by minimising distortion or size change. As residual stresses can exacerbate some forms of corrosion, stress relieving can often reduce or eliminate these effects.
- Stress relieving can reduce tension in welded structures.
- Source material that has been purchased in Harden and Temper condition must be stress relieved at a temperature around 50°C below previous tempering temperature to avoid reduced hardness.
- Whilst stress relieving can be carried out over a wide temperature range, when applied to ferrous materials it most commonly falls into two main temperature range categories:
- Welded steel structures are often stress relieved at 600°C to balance/stabilise welding stresses and reduce deleterious weld heat affected zone hardening effects.
- It is important that heating and cooling rates are appropriate to the process being undertaken and, for example, most ferrous metals need charging in the furnace at low temperatures, heating very slowly to the treatment temperature, soaking for a time sufficient to ensure through heating and optimum relief of stresses and then very slow cooling to a set maximum temperature.
- Heating and cooling too quickly may cause additional thermal stresses, thus defeating the object of the process.
- Components up to 1120mm diameter and 1730mm long can be treated vertically using special jigging. Weight up to 2000Kg
500°C -680°C provides a virtually complete stress relieve from machining, welding etc.
150°C -200°C partially relieves peak stresses normally introduced after hardening without significantly reducing base hardness.