MIL-DTL-12560K (MR)
3.2.2.1 Class 1 & 2. Class 1 and 2 steel shall have a CE of less than 0.80 wt% for plates less
than 2 inches in thickness. For plates 2 to 4 inches shall have a CE of less than 0.85 wt%. For
plates greater than 4 inches in thickness shall have a CE of 0.90 wt% or less.
3.2.2.2 Class 3. Class 3 steel shall have no CE limit unless otherwise specified in the contract or
purchase order (see 6.2).
3.2.2.3 Class 4a. Class 4a steel shall have a CE limit of less than 0.70 wt% unless otherwise
specified in the contract or purchase order (see 6.2).
3.2.2.4 Class 4b. Class 4b steel shall have no CE limit unless otherwise specified in the contract
or purchase order (see 6.2).
3.2.3 Heat treatment. All plates in each lot, including samples, shall receive the same heat
treatment except for such variations in tempering temperature as shall be necessary to produce
the prescribed hardness. The austenitizing temperature for production plates may vary within a
range of 50° above the temperature used for test plates, but in no case shall the plate surface
exceed 1800°F (see 6.6).
3.2.4 Condition. Unless otherwise specified in the contract or purchase order (see 6.2), plates
shall be in the as-heat treated condition. If descaling is required it shall be as specified in the
contract or purchase order (see 6.2). Plates shall not be pickled.
3.2.5 Processing controls.
3.2.5.1 Furnace survey requirements of heat treating furnaces. All furnaces that are used to heat
treat plates must be thermally surveyed. The initial survey is done once using the thinnest and
thickest gage plate. This shall be followed with annual surveys using any gage.
3.2.5.1.1 Thermal survey requirements of heat treating furnaces. Thermal surveys are conducted
as follows:
a. Three contact thermocouples must be used, both edges and in the middle across the
width of the plate.
b. A calibrated recording device and thermocouples must be used.
c. The test plate is run through the furnace using standard hold times.
d. Trial starts when plate exits heat-up zones, and ends when plate exits furnace.
e. Maximum temperature variability when plate is in soaking zones is +/- 25°F for
tempering furnaces and +/- 50°F for austenitizing furnaces.
3.2.5.2 Heating. Stress relieving the plates, local or general, shall be allowed after final
quenching and tempering at a maximum temperature of 50°F below the tempering temperature.
Plates shall not be stress relieved in a temperature range of 500-700°F. After stress relieving, the
plates shall be tested for hardness and shall meet the requirements of Table II.
3.2.5.3 Repairing.
3.2.5.3.1 Weld repair of mill defects after final heat treatment. Unless otherwise specified in the
contract or purchase order (see 6.2), weld repair after final heat treatment shall be permitted for
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