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· When a steel is normalized
it is taken into the temperature range where austenite
is stable and allowed to transform.
The product is then removed from the furnace and air cooled. This relatively
rapid cooling gives rise to a fine grained pearlitic
structure.
· Many processes cannot justify the cost of
furnace reheating to obtain a given microstructural or stress state. For these
processes, modification of the cooling profile to provide temperature holds
above the martensite
start temperature can produce a reduced stress
condition and different
microstructure.
· Two cooling
trajectories which satisfy these requirements are known as "Martempering"
in which a lower internal stress martensite is produced and "Austempering"
in which forms a bainititic
microstructure.
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