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 overheated mild steel were inserted. One peg was withdrawn and quenched at each of the temperatures indicated by the numbered arrows, and after suitable preparation these pegs were photographed in order to show the changes in structure taking place during heating and cooling operations. The illustrations here reproduced are selected from those photographs with the object of presenting pictorially the changes involved in the refining of overheated steel or steel castings. Figures 66 to 79 with their captions show much that is of value to steel users. [Illustration: FIG. 66.--The structure of overheated mild steel from which all the pegs were made (magnified 25 diameters). The pegs withdrawn at 720 deg.C., or earlier, had this structure and were quite soft.] [Illustration: FIG. 67.--Peg withdrawn at 750 deg.C. (magnified 25 diameters). The structure is apparently unaltered, but the peg was hard and, unlike the earlier ones, would not bend double.]