The process of hardening involves the following stages:
1. Heating: The steel to be heat treated is heated slowly in a furnace to atemperature 30C to 50C above the upper critical temperature i.e.,above the A3 line, as shown in Fig.2.8.
2. Soaking: The heated steel is held at this temperature for considerablelength of time to allow complete austenisation.
3. Cooling: The steel is cooled by quenching (in a water bath or oil bath) tothe room temperature. The cooling rate should be higher than the criticalcooling rate in order to get the completely martensitic structure.
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