Alloy Steel Product Guide

Chrome moly is an abbreviation for “chromium-molybdenum steel” (sometimes spelled “cro-mo”). Chrome moly is a range of low alloy steels used, for example, to produce tubing for bicycle frames and racecar roll cages. It is not as lightweight as aluminum alloys, but has the advantages of high tensile strength and malleability. It is also easily welded and is considerably stronger and more durable than standard 1020 steel tubing.

One of the most common chrome moly steels is 4130. 4130 chrome moly is an ideal material for BMX bicycle frames and firearms receivers because of its high tensile strength and high strength-to-weight ratio.

Although chrome moly contains chromium, it does not have the corrosion resistance of stainless steel.

4130 (Chrome moly) Normalized Alloy Steel  
Minimum PropertiesUltimate Tensile Strength, psi97,200
Yield Strength, psi63,100
Elongation25.50%
Rockwell HardnessB92
4130 (Chrome moly) Annealed Alloy Steel  
Minimum PropertiesTensile Strength, psi81,200
Yield Strength, psi52,200
Elongation28.20%
Rockwell HardnessB82
ChemistryIron (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%
4340 (Chrome moly) Normalized Alloy Steel  
Minimum PropertiesUltimate Tensile Strength, psi186,000
Yield Strength, psi125,000
Elongation12.20%
Rockwell HardnessB100
ChemistryIron (Fe)96%
Carbon (C)0.37 - 0.43%
Chromium (Cr)0.7 - 0.9%
Manganese (Mn)0.7% max
Molybdenum (Mo)0.2 - 0.3% max
Nickel (Ni)1.83%
Phosphorus (P)0.035% max
Sulphur (S)0.04% max
Silicon (Si)0.23%
8620 (chrome-nickel-moly) Alloy Steel  
Minimum PropertiesTensile Strength, psi97,000
Yield, psi57,000
Brinell Hardness201
Elongation25%
Machinability66%
ChemistryCarbon (C)0.18 - 0.23%
Manganese (Mn)0.7 - 0.9%
Phosphorus (P)0.35% Max
Sulphur (S)0.4% Max
Silicon (Si)0.15 - 0.35%
Chromium (Cr)0.4 - 0.6%
Nickel (Ni)0.4 - 0.7%
Molybdenum (Mo)0.15 - 0.25% max

Alcobra Metals states that all technical data is for comparison purposes only and is NOT FOR DESIGN. It has been compiled from sources we believe to be accurate but cannot guarantee. Please consult an Engineer.

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