Alloy Steel 4320

Principal Design Features

This is an oil hardening chromium, nickel, molybdenum low alloy steel of good strength and toughness, with relatively low carbon content for good weldability.



Machinability is good in the annealed condition, but difficult to machine once the alloy has been hardened by heat treatment. In the hardened condition it is best to use grinding operations.


Forming characteristic are good in the annealed condition.


Weldability of 4320 is good by all conventional methods.

Heat Treatment

Heat treatment response is best if the alloy is first normalized at 1650 F and air cooled. It then can be heat treated at 1500 F followed by an oil quench and tempering to desired hardness.


Forge at 2200 F down to 1900 F.

Hot Working

Hot working may be done at 1900 F down to 1600 F.

Cold Working

The alloy is readily cold worked, in the annealed condition, by conventional methods.


Anneal at 1600 F and slow furnace cool.


Not applicable to this alloy.


Tempering temperature depends upon hardness desired. Temper at 400 F to 1300 F. A 400 F temper will give a hardness of approximately 450 Brinell and a 1200 F temper will give 250 Brinell.


See “Heat Treatment” and “Tempering”. Also hardens by cold working.

Density: 0.28

Specific Gravity: 7.78

Specific Heat: 0.114

Melting Point: 2590

Thermal Conductivity: 23


MoETensile: 30


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