 | Annealing, Hardening, Tempering - Course: Working techniques of heat treatment of steel. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 27 p.) |
 |  | 6. Tempering |
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6.1. Types of Tempering
Tempering from outside:
The cold workpiece is slowly heated by means of appropriate heat sources and after having reached the tempering temperature (between 200°C and 500°C) it is cooled down.
Tempering from inside:
The workpiece is shortly quenched after having been hardened so that only outer layer is cold. The residual heat penetrates from inside, after having reached the tempering temperature it is cooled down.
The same effect can be reached when the workpiece is cooled down only on one side and the heat contained in the other part runs after again.
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After hardening the point to be tempered must be finished quickly by means of polishing linen cloth in order to recognize the temper colours! |
The approximate value for the tempering time for compact workpieces:
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1 to 1.5 hours for 20 mm thickness of workpiece |
Hints:
- The tempering effect is a combination of time and temperature. If the tune is enlarged, the temperature can be decreased.- For tools, longer tempering at lower temperature is better than shorter tempering at higher temperature.
- High-alloy steels require longer tempering times than unalloyed steels.
What is the purpose of
tempering?
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Which influence is exercised by the tempering temperature onto
the useful
hardness?
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Why it is possible to determine the temperature by means of
tempering
colours?
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