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Steel 4130 properties

AISI/SAE 4130 steel, UNS designation G41300, is a low-alloy chromium-molybdenum steel that achieves a tensile strength of approximately 560 MPa / 81200 psi in normalized condition. It belongs to the “cromoly” family of steels and is characterized by its excellent strength-to-weight ratio, good weldability and high toughness, making it a widely used material in aerospace, automotive, and structural component industries.

Chemical Composition

Section titled “Chemical Composition”

The chemical composition of 4130 steel is based on its controlled carbon content and the addition of chromium and molybdenum as hardening agents. Balance is iron.

Element Content (%)
Iron, Fe 97,03 – 98,22
Carbon, C 0,28 – 0,33
Chromium, Cr 0,80 – 1,10
Manganese, Mn 0,40 – 0,60
Silicon, Si 0,15 – 0,35
Molybdenum, Mo 0,15 – 0,25
Phosphorus, P ≤ 0,035
Sulfur, S ≤ 0,040

Physical Properties

Section titled “Physical Properties”

The physical properties of 4130 steel determine its behavior in service without considering the influence of external forces. Its typical density is 7,85 g/cm³ / 0.284 lb/in³.

Property Value
Density 7,85 g/cm³ / 0.284 lb/in³
Melting point 1432 °C / 2610 °F

Mechanical Properties

Section titled “Mechanical Properties”

The mechanical performance of 4130 steel varies significantly depending on the heat treatment condition and forming process. The machinability in annealed and cold drawn condition is 70 % relative to AISI 1212 steel.

Normalized and Annealed Condition

Property Normalized Condition Annealed Condition (Cold drawn)
Tensile strength 560 – 760 MPa / 81,2 – 110 ksi 590 – 760 MPa / 85 – 110 ksi
Yield strength 460 – 590 MPa / 66,7 – 85 ksi 480 – 590 MPa / 70 – 85 ksi
Young modulus 190 – 210 GPa / 27557 – 30458 ksi 190 – 210 GPa / 27557 – 30458 ksi
Elongation (in 50 mm) 20 – 30 % 20 – 30 %
Reduction of area 59,6 % –
Brinell hardness (HB) 217 –
Rockwell B hardness (HRB) – 90 – 96
Poisson’s ratio 0,27 – 0,30 0,27 – 0,30

Quenched and Tempered Condition

Oil or water quenching followed by tempering dramatically increases hardness and strength. Final values depend on tempering temperature and part diameter.

Diameter / Thickness (mm) Tensile strength (MPa / ksi) Minimum yield strength (MPa / ksi) Minimum elongation (%)
d ≤ 16 mm, t ≤ 8 mm / d ≤ 0,63 in, t ≤ 0,31 in 1100 – 1300 MPa / 160 – 190 ksi 900 MPa / 130 ksi 10 %
16 < d ≤ 40 mm, 8 < t ≤ 20 mm / 0,63 < d ≤ 1,57 in, 0,31 < t ≤ 0,79 in 1000 – 1200 MPa / 150 – 170 ksi 750 MPa / 109 ksi 11 %
40 < d ≤ 100 mm, 20 < t ≤ 60 mm / 1,57 < d ≤ 3,94 in, 0,79 < t ≤ 2,36 in 900 – 1100 MPa / 130 – 160 ksi 650 MPa / 94 ksi 12 %
100 < d ≤ 160 mm, 60 < t ≤ 100 mm / 3,94 < d ≤ 6,30 in, 2,36 < t ≤ 3,94 in 800 – 950 MPa / 116 – 138 ksi 550 MPa / 80 ksi 13 %
160 < d ≤ 250 mm, 100 < t ≤ 160 mm / 6,30 < d ≤ 9,84 in, 3,94 < t ≤ 6,30 in 750 – 900 MPa / 109 – 131 ksi 500 MPa / 73 ksi 14 %

Thermal Properties

Section titled “Thermal Properties”

Thermal conductivity and expansion values are critical for applications involving heating and cooling cycles. Typical thermal conductivity is approximately 42,7 W/m·K / 296 BTU·in/(h·ft²·°F) at 100 °C.

Property Value at 100 °C / 212 °F
Thermal conductivity 42,7 W/m·K / 296 BTU·in/(h·ft²·°F)
Specific heat 477 J/(kg·K) / 0,114 BTU/(lb·°F)

Heat Treatment

Section titled “Heat Treatment”

4130 steel responds effectively to conventional heat treatments to modify its microstructure and mechanical properties.

Austenitizing and Quenching Temperature

Austenitizing prior to quenching is typically performed between 830 °C and 870 °C / 1525 °F and 1600 °F. The quenching medium is usually oil, although thin sections can be quenched in water. The critical cooling rate is moderate, allowing uniform hardening in medium-thickness parts.

Tempering Curve

Tempering is performed immediately after quenching to reduce brittleness and adjust hardness. The typical tempering range is between 200 °C and 650 °C / 400 °F and 1200 °F. Tensile strength varies from 1300 MPa / 190 ksi with low tempering to 750 MPa / 109 ksi with high tempering, while ductility increases progressively.

Industrial Applications

Section titled “Industrial Applications”

4130 steel is used in sectors demanding high strength, guaranteed weldability, and structural reliability. It is used in both normalized and quenched and tempered conditions.

Industry Application
Aerospace Fuselage structural tubes, landing gear, engine mounts, and welded components subjected to vibration.
Automotive and racing Roll cages, racing chassis, driveshafts, lightened crankshafts, and flywheels.
Defense Armament parts and rifle components requiring case hardening by carburizing.
Oil and gas Drilling tools, valve bodies, and forged flanges for wellhead service.
Bicycles and motorcycles High-performance frames and seatposts welded with specific techniques (TIG), leveraging its lightness and fatigue resistance.

Comparison with Similar Materials

Section titled “Comparison with Similar Materials”

4130 steel offers an optimal balance between strength and ductility, with lower carbon content than other 41xx series steels, improving its weldability and toughness.

Material Carbon content (%) Tensile strength (normalized) Weldability Typical application
Steel 4130 0,28 – 0,33 560 – 760 MPa / 81,2 – 110 ksi Excellent, weldable with preheating and PWHT Structural tubes, chassis
Steel 4140 0,38 – 0,43 650 – 850 MPa / 94 – 123 ksi Good, requires stricter thermal control Shafts, heavy machinery gears
Steel 4340 0,38 – 0,43 750 – 900 MPa / 109 – 131 ksi Limited, difficult to weld due to high nickel content High-stress aircraft components, forged crankshafts
Steel 25CrMo4 (1.7218) 0,22 – 0,29 550 – 750 MPa / 80 – 109 ksi Excellent, behavior very similar to 4130 European equivalent of SAE 4130 per EN 10083

Sources Consulted

Section titled “Sources Consulted”