Alloy Steel 9840

Chemical Analysis
C% Carbon
0.38 – 0.43
Mn% Manganese
0.70 – 90.90 max
P% Phosphorus
0.035 max
S% Sulfur
0.040 max
Si% Silicon
0.15 – 0.30
Ni% Nickel
0.85 – 1.15
Mo% Molybdenum
0.20 – 0.30
Fe% Iron
95.945 – 97.02
Cr% Chromium
0.70 – 0.90

General characteristics of Alloy Steel 9840

This is a nickel-chrome-molybdenum steel with excellent hardenability, strength and toughness.


This alloy is suited to production of highly stressed components of large cross section for aircraft, automotive and general engineering applications, such as forged propeller shafts, connecting rods, gear shafts, crankshafts and landing gear components.


This alloy would be forged between 2150 and 1700ºF (1175 and 925ºC.)

Heat treatment

Annealing: Austenitize at 1525ºF (830ºC) and slow cool from 1280 to 1200ºF (iso anneal) to give coarse pearlite structure for optimum machinability.

Normalizing: At 1600ºF (870ºC) followed by air cool.

Hardening: from 1525-1575ºF (830-860ºC) and oil quench for thin, intricate shapes, water quench for large, simple shapes.

Tempering: from 1000-1250ºF(540-680ºC) as per required properties.

Machinability: this alloy may be readily machined, preferably from a coarse pearlitic structure.

Weldability: pre-heat and post-weld stress relief are recommended for welding of this alloy. Welding should not be carried out in the hardened and tempered condition.

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