Chromoly

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v • d • e Iron alloy phases
Austenite (γ-iron; hard) Bainite Martensite Cementite (iron carbide; Fe3C) Ledeburite (ferrite - cementite eutectic, 4.3% carbon) Ferrite (α-iron, δ-iron; soft) Pearlite (88% ferrite, 12% cementite) Spheroidite
Types of steel
Carbon steel (≤2.1% carbon; low alloy) Stainless steel (steel with chromium) HSLA steel (high strength low alloy) Tool steel (very hard)
Other iron-based materials
Cast iron (>2.1% carbon) Wrought iron (contains slag) Ductile iron

Chromoly is an abbreviation for "chromium-molybdenum steel" (sometimes spelled "cro-mo"). Chromoly is a range of low alloy steels used, for example, to produce tubing for bicycle frames and race-car 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 chromoly steels is 4130 steel, composed of 0.28 to 0.33% carbon, 0.4 to 0.6% manganese, 0.8 to 1.1% chromium, 0.15 to 0.25% molybdenum, 0.04% phosphorus, 0.04% sulfur, and 0.2 to 0.35% silicon, in addition to iron. 4130 chromoly is an ideal material for BMX bicycle frames and AK-47 receivers because of its high tensile strength and high strength-to-weight ratio.

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

Chromoly is also a popular material used in manufacturing aftermaket clutch/flywheel components for cars with standard transmissions.