Double Annealing
:
HARDENING CARBON STEEL FOR TOOLS
:
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.