4140 Alloy Steel Data Sheet

  4140 is an alloy steel that is supplied in either the annealed or prehardened condition. The prehardened condition is heat treated to a medium hardness (HRC 28/32) and is designated as 4140 HT. 4140 annealed is supplied in the soft condition and can be hardened to RC 54. 4140 annealed is designated as 4140 Ann or simply 4140. 4140 HT is supplied in many forms such as hot rolled or turned, ground and polished rounds and block or DCF plate to be used as a holder material for high strength structural components.
Typical Chemistry
Carbon 0.42%
Silicon 0.30%
Molybdenum 0.20%
Manganese 1.00%
Chromium 1.00%
Typical Applications
  Support Plates Filler Blocks
  Punch Holders Structural Parts
  Clamps Base Plates
  Gages Molds
  Brake Dies Jigs
  Fixtures Tool Holders
  High-Strength Parts

Annealed Hardness: BHN 185/200.

Thermal Treatments.
Annealing: 1550F (840C), hold 2 hours, slow cool 50F(30C)/hr. max. to 1200F (650C), then air or furnace cool. Hardness BHN 185/200.

Stress Relieving:

Annealed Material: 1100-1300F (595-740C), hold 2 hrs, air cool.

Hardened Material: 50-100F (30-55C) below last tempering temperature, hold 2 hrs, air cool.

Straightening: Best done warm 400-800F (205-425C)

Hardening: (Atmosphere or Vacuum Furnace)

Preheat: 1250-1300F (675-705C), equalize

High Heat: 1550-1600F (840-870C), 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 (650C). Temper immediately. Water quenching from 1550F (840C) may be used for simple shapes and larger sections. Note vacuum furnaces must have oil quench capability to achieve comparable results.

Temper: Tempering at 400-1200F (205-650C) for 1 hour per inch (25mm) of thickness at temperature is recommended (2 hrs min). Air cool to room temperature.


Medium carbon steel filler material.

Annealed Material:
Preheat: 400F (205C)
Postheat: 500-600F (260-315C)

Hardened Material:
Preheat: 50F (30C) less than last tempering temperature.
Postheat: 50F (30C) less than last tempering temperature.

Physical Properties
Modulus of Elasticity .......................29 psi x 106(200 GPa)
Specific Gravity ......................................................(7.81)
Density ........................................0.282 lb/in3(7810 kg/m3)

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