AISI 4340
Alloy Steel
Typical Chemistry
Carbon 0.40%
Manganese 0.70%
Silicon 0.30%
Chromium 0.80%
Molybdenum 0.25%
Nickel 1.85%
Typical Applications
Arbors Forging Dies
Crankshafts Gears
Die Blocks Pressure Vessels
Fittings Shafting

Annealed Hardness: BHN 217/248

Thermal Treatments
Critical Temperature: 1380F (750C).
Annealing: 1550F (840C), hold 2 hours, slow cool 50’F (30°C)/ hr max. to 1000F (540C), then air or furnace cool. Hardness BHN 217/248.
Stress Relieving:
Annealed Material: 1100-1300F (595-740C), hold 2 hrs, air cool.
Hardened Material: 50-100°F (30-55°C) below last tempering temperature, hold 2 hrs, air cool.
Straightening: Best done warm 400-800F (205-425C).
Hardening: (Atmosphere or Vacuum Furnace).
Preheat: 1200-1250 (650-675C), equalize.
High Heat: 1475-1500F (800-815C), soak 10 to 30 minutes. For vacuum hardening, use the high side of the high heat range and soak times.
Quench: Oil quench to hand warm, 150F (65C). Temper immediately. Note: Vacuum furnaces must have oil quench capability.
Temper: Tempering at 400-1200F (205-650C) for 1 hour per inch (25mm) of thickness at temperature is recommended. Air cool to room temperature.

Physical Properties
Modulus of Elasticity .........................................30 psi x 106(207 GPa)
Specific Gravity ...................................................................................7.84
Density ..............................................................0.283 lb/in3(7840 kg/m3)
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