Areas of application
The objective of intermediate annealing is to optimise the crystalline structure of the material and thus improve its mechanical properties. Depending on the material and application, intermediate annealing can also help to increase corrosion resistance and resistance to high temperatures.
Intermediate annealing can be used directly during the production process of a workpiece, for example after case hardening. For this, after carburising or grain refining, the workpiece is heated below the lower transformation point for an extended period, and then slowly cooled.
The process is also used to extend the service life of previously used components, for example moulded steel components in die casting moulds. The temperature changes resulting from use have created stresses in the components, and these are now relieved.
In quenched and tempered steel parts , intermediate annealing corresponds, in principle, to a tempering treatment. The selected temperature is between 30 °C and 50 °C lower than the tempering temperature during production. The dwell time is between two and four hours. This type of intermediate annealing can be repeated after the component was used for a further period.
The advantages at a glance
Intermediate annealing offers various advantages for workpieces in production, and for components already in use:
- Reduced stresses
- Improved formability
- Improved workability
- No cracking, even in multi-stage transformation processes
- Longer service life
Recrystallisation annealing of steel
Recrystallisation annealing is performed after cold-forming, especially during the cold drawing and cold rolling of wires and sheets. The annealing at recrystallisation temperatures between 550 °C and 700 °C relieves stresses in the steel and repairs the crystalline structure. A α-ferrite-austenite phase transformation does not take place.
The objective of recrystallisation annealing is to achieve a fine-grain microstructure . This requires the microstructure to contain crystals to be as elongated as possible. This is the case only from a deformation degree of approx. 20%. If merely the critical deformation degree of 5% to 15% is reached, it is advisable to use normal annealing, because the low nucleus count during recrystallisation annealing would produce a coarse grain.
The recrystallisation temperature and duration depend on the degree of deformation and the melting temperature of the material. For thin parts, 10 minutes at 700 °C may be enough, while thicker parts usually require one hour at 600 °C to 650 °C.
Process locations
Härtha provides intermediate annealing at various locations. To learn more, refer to our interactive location overview.