Application
Annealing
Microstructure Improvement and Stress Relief for Better Workability
Annealing treatments are versatile heat treatment processes for targeted modification of the metallic microstructure. Depending on the goal (softening, grain refinement, stress relief or reversal of work hardening), temperature, holding time and cooling rate differ considerably.
NTH Therm supplies chamber furnaces and bogie-hearth furnaces with precise temperature control and programmable cooling ramps for all common annealing processes.
Annealing Processes Compared
| Process | Temperature | Purpose |
|---|---|---|
| Normalising | 800–950 °C | Grain refinement, uniform microstructure |
| Full / Spheroidising annealing | 680–860 °C | Maximum machinability, spheroidal carbides |
| Stress-relief annealing | 450–650 °C | Residual stress removal without microstructure change |
| Recrystallisation annealing | 500–750 °C | Reversal of work hardening |
| Diffusion annealing | 1000–1200 °C | Homogenisation of segregations |
Typical Materials and Components
- Carbon and low-alloy steels after forming, welding or forging
- Cold-rolled strip and sheet (recrystallisation annealing)
- Welded structures, castings, drop forgings (stress-relief annealing)
- Tool steels before further machining (spheroidising annealing)
Recommended NTH Therm Furnace Systems
- Chamber Furnace ICO: forced-air to 750 °C, for stress-relief and recrystallisation annealing
- Chamber Furnace ICF: to 1300 °C, for diffusion annealing and high-alloy steels
- Bogie-Hearth Furnace IWF / IWO: for large-format forgings, welded structures and castings
- Bell-Type Furnace: for coils, rolls and stacked charges
Frequently Asked Questions
What are the most common annealing processes in metalworking?
The most widely used processes are: normalising (grain refinement, 800–950 °C), full annealing/spheroidising (maximum machinability, 680–860 °C), stress-relief annealing (residual stress removal, 450–650 °C) and recrystallisation annealing (reversing work hardening, 500–750 °C).
Why is a controlled cooling rate important in annealing?
Cooling too rapidly can introduce new residual stresses or stabilise undesirable phases. Full (spheroidising) annealing requires very slow furnace cooling (< 20 K/h) to fully transform carbides into spheroidal form.
Can annealing be carried out under protective atmosphere?
Yes, particularly for bright or pre-treated surfaces we recommend bright annealing under N₂ or H₂. NTH Therm equips suitable chamber furnaces with atmosphere control on request.