S7 is a shock-resistant air hardening tool steel, designed for high impact resistance at relatively high hardness. It offers toughness to withstand chipping and breaking, combined with high attainable hardness and good wear resistance.
Preheat: 1100/1250F (595/675C), equalize, 1350/1450F (775/790C), equalize.
Austenize: 1725/1775F (995/895C), 30/45 minutes at temperature.
Quench: Air, positive pressure vacuum to 150F (65C), Interrupted oil to 150F(65C). Sections over 3″ thick may require oil quenching to attain full hardness.
Temper: 350/1000F (205/540C), hold 2 hours at temperature, air cool. Temper twice.
Cryogenic Treating: Refrigeration treatments may improve long term dimensional stability by transforming retained austenite. Refrigeration treatments should generally be performed after the first temper, and must be followed by a temper.
Hardness and Impact Toughness Data
Air cooled from 1775F(970C)
Tempering |
Toughness |
|||
| Temperature | Hardness | Charpy C-Notch | ||
| Deg. F | Deg. C | HRC | Ft. Lbs. | Joules |
| As quenched | 59 | - | - | |
| 300 | 150 | 59 | 85 | 115 |
| 400 | 205 | 57 | 125 | 169 |
| 500 | 260 | 55 | 125 | 169 |
| 600 | 315 | 54 | 115 | 155 |
| 700 | 379 | 53 | 105 | 141 |
| 800 | 425 | 53 | 1050 | 141 |
| 900 | 480 | 52 | 120 | 162 |
| 1000 | 540 | 51 | 150 | 203 |
| 1100 | 595 | 47 | 190 | 257 |
Because of the low tempering temperatures normally used, S7 is not typically suitable for nitriding or similar treatments.
A. Heat to 1550F (840C), hold 2 hours, slow cool 50F (30C)/hour maximum) to 1000F (540C), air cool.
OR
B. Heat to 1550F (840C), hold 2 hours, cool to 1400F (760C), hold 4 hours, air cool to room temperature.
Typical annealed hardness: 187/220 BHN.
Annealed Material: Heat to 1200/1250F(650/675C), hold two hours, cool in still air.
Hardened Material: Heat to 25F(15C) below original tempering temperature, hold two hours, cool in still air.
Use hot work tool steel filler material 4140 or 4150 type filler material may be satisfactory for small repairs or welds away from working surface of tool.
Annealed Material: Preheat to 400/600F(205/315C). Maintain above 400F(205C) during welding. Reanneal or temper 1400F(760C) for 4 hours after welding.
Hardened Material: Preheat to original tempering temperature (300F(150C) minimum). Maintain above 300F(150C) during welding. Cool to 150F(65C) after welding. Temper 25F(15C) below original tempering temperature. (300F(150C) Minimum)
Modulus of Elasticity 30psix10(6) (207 GPa)
Density 0.283 lb/in3 (7861 kg/M3)
Thermal Conductivity 16.5 BTU/hr./ft./F 29 W/m/ °K)
