Alloy Steel 4130


4130 Chromium-Molybdenum Steel


4130 (Chromoly) Normalized Alloy Steel

Minimum Properties Ultimate Tensile Strength, psi 97,200
Yield Strength, psi 63,100
Elongation 25.5%
Rockwell Hardness B92

4130 (Chromoly) Annealed Alloy Steel

Minimum Properties Tensile Strength, psi 81,200
Yield Strength, psi 52,200
Elongation 28.2%
Rockwell Hardness B82
Chemistry Iron (Fe) 97.3 – 98.22%
Carbon (C) 0.28 – 0.33%
Chromium (Cr) 0.8 – 1.1%
Manganese (Mn) 0.4 – 0.6%
Molybdenum (Mo) 0.15 – 0.25%
Phosphorus (P) 0.035% max
Sulphur (S) 0.04% max
Silicon (Si) 0.15 – 0.35%

Principal Features

AISI 4130 is a low alloy steel containing molybdenum and chromium as strengthening agents. The carbon content is nominally 0.30% and with this relatively low carbon content the alloy is excellent from the fusion weldability standpoint. The alloy can be hardened by heat treatment.


Typical applications for 4130 low alloy steel include. structural use such as aircraft engine mounts and welded tubing applications.


This alloy is readily machined by conventional methods. Machinability is best with the alloy in the normalized and tempered condition. Although the alloy may be machined in the fully heat treated condition, machinability becomes more difficult with increasing strength (hardness) of the alloy.


Formability is best in the annealed condition for which the ductility is very good, Bend radii of 1t on annealed sheet material may be made.


4130 alloy is noted for its weldability by all of the commercial methods.

Heat Treatment

Heating at 1600 F followed by an oil quench will harden the 4130 alloy. For best results a normalizing pre-hardening heat treatment may be used at 1650 to 1700 F followed by the 1600 F soak and oil quench.


Forge at 2200 F maximum down to 1750 F.

Hot Working

4130 in the annealed condition has excellent ductility. Thus it is usually not necessary to do hot working to form parts. If hot working is needed it can be done in the range of 2000 F to 1500 F.

Cold Working

Cold working by conventional methods is readily accomplished on this alloy.


4130 (and most of the other low alloy steels) may be annealed at 1550 F for a time long enough to allow thorough heating of the section size. It should then be cooled in the furnace at a rate of less than 50 F per hour down to 900 F, followed by air cooling from 900 F.


Not applicable to this alloy.


Tempering is done to restore some of the ductility that may be lost after the hardening heat treatment and quench. Alloy 4130 is tempered at between 750 F and 1050 F, depending upon the strength level desired. The lower the tempering temperature the greater the strength.


Hardening is accomplished by heat treatment or by cold working — see “Heat Treatment”.

Other Comments

The 4130 alloy is a through hardening alloy and should not be case hardened.

Physical Properties:

Density (lb / cu. in.) 0.283
Specific Gravity 7.8
Specific Heat (Btu/lb/Deg F – [32-212 Deg F]) 0.114
Melting Point (Deg F) 2610
Thermal Conductivity 22.3
Mean Coeff Thermal Expansion 7
Modulus of Elasticity Tension 29