6. Quench.
7. Reheat to 250-500 deg.F. and cool slowly.

_Heat Treatment M_

After forging or machining:
1. Heat to 1,450-1,500 deg.F.
2. Quench.
3. Reheat to 500-1.250 deg.F. and cool slowly.

_Heat Treatment P_

After forging or machining:
1. Heat to 1,450-1,500 deg.F.
2. Quench.
3. Reheat to 1,375-1,450 deg.F. slowly.
4. Quench.
5. Reheat to 500-1,250 deg.F. and cool slowly.

_Heat Treatment Q_

After forging:
1. Heat to 1,475-1,525 deg.F. (Hold at this temperature one-half hour,
to insure thorough heating.)
2. Cool slowly.
3. Machine.
4. Reheat to 1,375-1,425 deg.F.
5. Quench.
6. Reheat to 250-550 deg.F. and cool slowly.

_Heat Treatment R_

After forging:
1. Heat to 1,500-1,550 deg.F.
2. Quench in oil.
3. Reheat to 1,200-1,300 deg.F. (Hold at this temperature three hours.)
4. Cool slowly.
5. Machine.
6. Reheat to 1,350-1,450 deg.F.
7. Quench in oil.
8. Reheat to 250-500 deg.F. and cool slowly.

_Heat Treatment S_

After forging or machining:
1. Carbonize at a temperature between 1,600 and 1,750 deg.F.
(1,650-1,700 deg.F. Desired.)
2. Cool slowly in the carbonizing mixture.
3. Reheat to 1,650-1,750 deg.F.
4. Quench.
5. Reheat to 1,475-1,550 deg.F.
6. Quench.
7. Reheat to 250-550 deg.F. and cool slowly.

_Heat Treatment T_

After forging or machining:
1. Heat to 1,650-1,750 deg.F.
2. Quench.
3. Reheat to 500-1,300 deg.F. and cool slowly.

_Heat Treatment U_

After forging:
1. Heat to 1,525-1,600 deg.F. (Hold for about one-half hour.)
2. Cool slowly.
3. Machine.
4. Reheat to 1,650-1,700 deg.F.
5. Quench.
6. Reheat to 350-550 deg.F. and cool slowly.

_Heat Treatment V_

After forging or machining:
1. Heat to 1,650-1,750 deg.F.
2. Quench.
3. Reheat to 400-1,200 deg.F. and cool slowly.

RESTORING OVERHEATED STEEL

The effect of heat treatment on overheated steel is shown graphically
in Fig. 65 to the series of illustrations on pages 137 to 144. This
was prepared by Thos. Firth & Sons, Ltd., Sheffield, England.

[Illustration: FIG. 65.--Chart of changes due to heating and cooling.]

The center piece Fig. 65 represents a block of steel weighing about
25 lb. The central hole accommodated a thermo-couple which was attached
to an autographic recorder. The curve is a copy of the temperature
record during heating and cooling. Into the holes in the side of
the block small pegs of