Steel alloy 4130 also known as ST4130, AISI 4130 or Chrome Moly is a general-purpose alloy steel containing molybdenum and chromium as strengthening agents. This alloy is widely used by the aviation and motorsports industries due to its weldability (due to its relatively low carbon content) fabrication, and mild hardenability in all offered forms/shapes (tubes, bars, sheets and plates). The alloy can be hardened by heat treatment. Typical uses include structural such as aircraft engine mounts and welded tubing applications.
Available in two different material states, also called conditions (Normalized and Annealed) depending on the process of how the material is heated and cooled. The cooling rate of normalizing (sometimes referred to as "Condition N") is slightly faster than that of annealing (sometimes referred to as "Condition A"), and the degree of supercooling is larger. Also, the structure obtained after normalizing is relatively fine, and the strength and hardness are higher than that of annealing.
The choice between Normalizing and Annealing
Machinability
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.The hardness after normalizing is significantly higher than that of annealing, and it is difficult to perform cutting processing. Normalizing relieves internal stress on steel and improves toughness in steels that may harden after the cold working process. The Annealed condition is the softer and formable condition and is best used when forming and improved machinability is needed. Annealing relieves internal stresses, softens and makes the material more ductile.
Forming
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. The harder and stronger Normalized condition is best used when forming is not needed.
Welding
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.
Forging
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.
Annealing
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.
Tempering
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
Hardening is accomplished by heat treatment or by cold working.
Properties
4130 (Chromoly) Normalized Alloy Steel
Ultimate Tensile Strength, psi 97,200 (min)
Yield Strength, psi 63,100 (min)
Elongation 25.5% (min)
Rockwell Hardness B92 (min)
4130 (Chromoly) Annealed Alloy Steel
Tensile Strength, psi 81,200 (min)
Yield Strength, psi 52,200 (min)
Elongation 28.2% (min)
Rockwell Hardness B82 (min)
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