T.O. 1-1A-9
2-62. SOAKING PERIODS. The period of soaking is governed by both the size of the section and the nature of the
steel. Table 2-1 indicates in a general way the effect of size on the time for soaking. This table is intended to be used as
a guide only and should not be construed as being a mandatory requirement. It applies only to plain carbon and low alloy
steels.
TABLE 2-1. SOAKING PERIODS FOR HARDENING NORMALIZING AND ANNEALING
(PLAIN CARBON STEEL)
TIME OF
HEATING TO
DIAMETER
REQUIRED
TIME OF
OR
TEMPERATURE HOLDING
THICKNESS
(APPROX)
(APPROX)
INCHES
HOURS
HOURS
1 and less
3/4
1/2
Over 1 thru 2
1 1/4
1/2
Over 2 thru 3
1 3/4
3/4
Over 3 thru 4
2 1/4
1
Over 4 thru 5
2 3/4
1
Over 5 thru 8
3 1/2
1 1/2
2-63. HARDENING. Temperatures required for hardening steel are governed by the chemical composition of the steel,
previous treatment, handling equipment, size and shape of piece to be treated. Generally, parts of heavy cross section
should be hardened from the high side of the given temperature range.
2-64. TEMPERING (DRAWING.) Tempering consists of heating the hardened steel to the applicable temperature
holding at this temperature for approximately 1 hour per inch of the thickness of the largest section, and cooling in Air or
quenching in oil at approximately 27 to 66 C (80 to 150°F). The temperature to be used for tempering of steel
depends upon the exact chemical composition, hardness, and grain structure obtained by hardening and the method of
tempering. The tempering temperatures given are only approximate, and the exact temperature should be determined
by hardness or tension test for individual pieces. The final tempering temperatures should not be more than 111
C
(200 F) below the tempering, temperature given. If the center of the section is more than 1/2-inch from the surface, the
tensile strength at the center will in general be reduced; therefore, a lower tempering temperature should be used for
sections thicker than 1 inch in order to obtain the required tensile strength.
2-65. ANNEALING. Annealing consists of heating to the applicable temperature, holding at this temperature for
approximately the period of time given, and cooling in the furnace to a temperature not higher than 482
C (900 F). The
steel may then be removed from the furnace and cooled in still air.
2-66. NORMALIZING. Normalizing consists of heating the steel to the applicable temperature, holding at this
temperature for period of time, removing from furnace and cooling in still air.
2-67. CARBURIZING. Carburizing consists of heating the steel packed in a carburizing medium, in a closed container,
to the applicable temperature and holding at this temperature for the necessary period of time to obtain the desired depth
of case. 1020 steel will require 1 to 3 hours so a carburizing temperature of 899-C (1650F) for each 1/64 inch of case
depth, required. Parts may be cooled in the box or furnace to a temperature of approximately 482
C (900 F) then air
cool. This treatment leaves the alloy in a relatively soft condition and it is then necessary to condition by heating and
quenching, first for core refinement, followed by heating and quenching for case hardness. Alloy may be quenched
directly from the carburizing furnace, thus producing a hard case and a core hardness of Rockwell B67. This treatment
produces a coarse grain in some types of steel and may cause excessive distortion. Usually there is less distortion in
fine grain steels. The core treatment outlined above refines the grain as well as hardens.
2-12
