Forging Alloy Steel 4320

Chemical Analysis
C Carbon
0.17 – 0.22
Mn Manganese
0.45 – 0.65
P Phosphorus
0.04 max
S Sulfur
0.04 max
Si Silicon
0.20 – 0.35
Ni Nickel
1.65 – 2.00
Cr Chromium
0.40 – 0.60
Mo Molybdenum
0.20 – 0.20

General Characteristics of AISI 4320

AISI 4320 is a nickel-chromium – molybdenum case – hardening steel that displays good strength, hardenability and toughness.

Forging Applications

AISI 4320 is used in the manufacturing of forged gears and pinions and other heavy-duty machinery components.

AISI 4320 Forgings

AISI 4320 would be forged at a temperature of around 2200 – 2250ºF (1205 – 1235ºC) and might be forged down to a temperature in the region of 1650 – 1700ºF (900 – 925ºC) and subsequently air cooled.

Heat Treatment

Annealing: AISI 4320 might be processed through case hardening and subsequent heat treatment operations without the need for annealing. Its microstructure as forged will be suitable for such treatments, but in the case of small sections where a very fine structure may result from forging, a normalizing treatment would be recommended prior to further heat treatment.

Normalizing: AISI 4320 is normalized at a temperature of around 1700ºF (925ºC.) Air cooling follows heat treatment. It should be noted that experience alone will determine the normalizing temperature for a specific part following given forging conditions.

Hardening: AISI 4320 should be austenitized following carburizing at a temperature in the region of 1525 -1550ºF (830 – 845ºC) followed by oil quenching.

Tempering: The alloy will be tempered at a temperature that will most probably be based on past experience, according to required mechanical properties.

Machinability: The alloy is readily machinable in the forged – depending upon section size – condition or following normalizing. Finish machining following harden and temper is applicable.

Weldability: AISI 4320 is readily weldable by all normal methods. The alloy should however be welded in the as-forged or normalized conditions only, and not following harden and temper.

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