Stress relieving is carried out on metal products in order to minimise residual stresses in the structure thereby reducing the risk of dimensional changes during further manufacturing or final use of the component. This treatment can actually be applied to the full range of steels or a combination of.
What are the applications and benefits?
Stress relieving is applied to both ferrous and non-ferrous alloys and is intended to remove internal residual stresses generated by prior manufacturing processes such as machining, cold working and welding. Without it, subsequent processing may cause unacceptable distortion and/or the material can suffer from service problems such as stress corrosion cracking. The treatment is not intended to produce significant changes in material structures or mechanical properties, and is therefore normally restricted to relatively low temperatures.
How does the process work?
Material is loaded into the furnace at a low temperature that is then raised slowly so that thermal stresses are not induced. Once up to temperature the material is held there before cooling slowly to once again avoid the induction of thermal stresses. Finally the steel is still air cooled outside of the furnace to ambient.
The residual stress level after stress-relief will be maintained only if the cool down from the soak temperature is controlled and slow enough that no new internal stresses arise. New stresses that may be induced during cooling depend on the cooling rate, the cross-sectional size of the workpiece, and the composition of the steel. For plain carbon and low-alloy steels, the temperature to which the specimen is heated is usually between 450°C and 650˚C, whereas for hot-working tool steels and high-speed steels it is between 600°C and 750˚C.
The final product exhibits a dusty red finish easily removable by shot blasting. As an alternative to shot blasting the heat treatment can be processed in sealed retorts to minimise the scaling effect.
Which materials can be treated?
Typical steels treated include: AISI 4130, AISI 8630, F70, F22, F65, F52, AISI 4140
How can Con Mech Engineers help?
At Con Mech we can follow any thermal profile extremely accurately both in raising and lowering the temperature. Tight temperature tolerances must be followed so as not to diminish any mechanical properties in the steel. This is particularly important when dealing with already hardened and tempered products.