AISI / Alloy Steel 8720

Chemical Analysis
C% Carbon
0.18 – 0.23
Mn% Manganese
0.70 – 0.90
P% Phosphorus
0.035 max
S% Sulfur
0.040 max
Si% Silicon
0.20 – 0.35
Ni% Nickel
0.40 – 0.70
Cr% Chromium
0.40 – 0.60
Mo% Molybdenum
0.20 – 0.30

General characteristics of Alloy Steel 8720

Alloy steel 8720 is a case-hardening low-alloy steel containing nickel, chromium and molybdenum as alloying elements.


This alloy may be used in the production of medium-strength parts such as forged camshafts, fasteners and gears.


This alloy is forged at a start temperature of around 2250ºF (1230ºC) and could be forged down to approximately 1700ºF(925ºC.) The alloy is air cooled after forging.

Heat treatment

Annealing: For optimum machinabilty, an as-forged structure is normally sufficient for this grade of alloy steel. If this proves not to be the case then an iso-anneal from around 1650ºF (900ºC) to 1225ºF (660ºC) will improve machinability.

Normalizing: 1700ºF (925ºC) and air cool. This is another method of improving machinability in this grade; normalizing might also be used prior to case hardening.

Hardening: The alloy will be austenitized at around 1550ºF (840ºC) and oil or water quenched depending upon section size and intricacy.

Tempering : to desired hardness, using temperatures based on past experience, following water or oil quench.

Machinability:This grade of alloy is readily machined following suitable heat treatment.

Weldability: This steel may be welded by normal fusion methods, but prior to any heat treatment that will modify the steel’s properties.

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