Stress relief annealing
| temperature | colour |
|---|---|
| 550 ° C | Dark brown |
| 630 ° C | Brownish red |
| 680 ° C | Dark red |
| 740 ° C | Dark cherry red |
| 780 ° C | Cherry red |
| 810 ° C | Light cherry red |
| 850 ° C | Bright red |
| 900 ° C | Good bright red |
| 950 ° C | Yellow Red |
| 1000 ° C | Light yellow bread |
| 1100 ° C | yellow |
| 1200 ° C | Light yellow |
| > 1300 ° C | Yellow white |
The stress-relief annealing is carried out with the purpose of the workpiece internal stresses degrade. In the case of steel, it is usually carried out in a temperature range of 550 to 650 ° C, whereby the material begins to flow plastically according to the stresses.
Definition according to EN 10052
Annealing at a temperature below the onset of austenite formation is in the material-dependent Z EIT T emperature U (also: mwandlungsschaubild TTT diagram ) to Ac1 (Fr .: A rrêt point c hauffage 1 hereinafter). The temperatures are mostly below 650 ° C, followed by slow cooling to reduce internal stresses without any significant change in the properties.
Purpose and application
The workpieces treated with this process experienced their stresses mainly as a result of uneven cooling after casting , welding , forging or other thermal processes. Heavy mechanical processing ( milling , turning , planing , deep drawing , cold forming , etc.) often requires stress relief annealing . Without this manufacturing step , such tensions would be released during further processing and subsequent heat treatments and lead to geometric deviations due to distortion . The strain hardening introduced by cold forming in the deformation zones, on the other hand, is removed by means of recrystallization annealing .
However, the stresses are not completely relieved (hence the term stress- relieved glow). The annealing reduces the yield point and maximum tensile strength temporarily (i.e. for the duration of the heating), which forces the material to flow plastically in accordance with the stresses. Tensions up to the size of the yield point remain at the annealing temperature.
Internal workpiece stresses are relieved by stress relief annealing before finishing. This reduces unwanted distortion in the final mechanical fine machining.
Stainless steels with niobium and tantalum components must not be stress relieved.
process
During stress relief annealing, the workpieces are heated slowly and evenly to around 580 ° C. This temperature is then held in the subsequent holding time. The decisive process is the slow and even cooling phase, which takes place in the annealing furnace. If it cools down too quickly, tensions and even cracks can arise in the material.
Advantages of stress relief annealing
- Low warpage processing
- shorter processing times due to a smaller allowance
- Proven longer tool life
- Avoidance of hardening cracks in the downstream heat treatment
- Advantages in automation, especially when using clamping systems
literature
- Hans-Jürgen Bargel, Günter Schulze u. a .: Materials science, VDI book. 10th edited edition. Springer, Berlin 2008, ISBN 978-3-540-79297-0 .
- Wolfgang Weißbach: Materials science and material testing. 15th edition. Vieweg, Wiesbaden 2004, ISBN 3-528-11119-4 .
Web links
Individual evidence
- ^ Ulrich Fischer: Metal table book . 41st edition. Verlag Europa-Lehrmittel Nourney, Vollmer, 2001, ISBN 3-8085-1721-2 , p. 128B.
- ↑ Stress relief annealing . In: www.meusburger.com. July 26, 2016, accessed August 1, 2016 .
- ↑ Advantages of stress relief annealing ( Memento from January 20, 2016 in the Internet Archive )