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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.