Double Annealing

: The Working Of Steel

Water annealing consists in heating the piece, allowing it to cool

in air until it loses its red heat and becomes black and then

immediately quenching it in water. This plan works well for very

low-carbon steel; but for high-carbon steel what is known as the

double annealing treatment must be given, provided results are

wanted quickly. The process consists in heating the steel quickly to

200 deg. or more above the upper critical, cooling in air down through

the recalescence point, then reheating it to just above the critical

point and again cooling slowly through the recalescence, then quenching

in oil. This process retains in the steel a fine-grained structure

combined with softness.