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Tempering should be
carried out as soon as possible following completion of quenching.
Heat
to within the 550°C / 650°C range soaking at temperature for one to
three hours according to section. A second temper holding at
temperature for at least one hour is essential and care must be taken to
ensure that the tools cool to room temperature between cycles. For
applications where thermal fatigue is of prime importance a third
tempering operation is recommended. The curve given provides
typical hardness values obtained on air cooling from 1020°C and double
tempering. |
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