g is just to relieve
strains, slow heating is not necessary, but the steel must be brought
up to a temperature not much less than a forging or rolling heat
and gradually cooled. Covering in this case is only necessary in
steel of a carbon content of more than 40 points.

ANNEALING IN BONE

Steel and cast iron may both be annealed in granulated bone. Pack the
work the same as for case-hardening except that it is not necessary
to keep the pieces away from each other. Pack with bone that has
been used until it is nearly white. Heat as hot as necessary for
the steel and let the furnace cool down. If the boxes are removed
from furnace while still warm, cover boxes and all in warm ashes
or sand, air slaked lime or old, burned bone to retain heat as
long as possible. Do not remove work from boxes until cold.

ANNEALING OF RIFLE COMPONENTS AT SPRINGFIELD ARMORY

In general, all forgings of the components of the arms manufactured
at the Armory and all forgings for other ordnance establishments
are packed in charcoal, lime or suitable material and annealed
before being transferred from the forge shop.

Except in special cases, all annealing will be done in annealing
pots of appropriate size. One fire end of a thermo-couple is inserted
in the center of the annealing pot nearest the middle of the furnace
and another in the furnace outside of but near the annealing pots.

The temperatures used in annealing carbon steel components of the
various classes used at the Armory vary from 800 deg.C. To 880 deg.C. or
1,475 to 1,615 deg.F.

The fuel is shut off from the annealing furnace gradually as the
temperature of the pot approaches the prescribed annealing temperature
so as to prevent heating beyond that temperature.

The forgings of the rifle barrel and the pistol barrel are exceptions
to the above general rule. These forgings will be packed in lime
and allowed to cool slowly from the residual heat after forging.

CHAPTER VII

CASE-HARDENING OR SURFACE-CARBURIZING

Carburizing, commonly called case-hardening, is the art of producing
a high-carbon surface, or case, upon a low carbon steel article.
Wrenches, locomotive link motions, gun mechanisms, balls and ball
races, automobile gears and many other devices are thereby given
a high-carbon _case_ capable of assuming extreme hardness, while
the interior body of metal, the _core_, remains soft and tough.

The simplest method is to heat the piece to be hardened to a br