Chromoly

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Iron alloy phases
Austenite (γ-iron; hard) Bainite Martensite Cementite (iron carbide; Fe3C) Ledeburite (ferrite - cementite eutectic, 4.3% carbon) Ferrite (α-iron; soft) Pearlite (88% ferrite, 12% cementite) Spheroidite
Types of Steel
Plain-carbon steel (up to 2.1% carbon) Stainless steel (alloy with chromium) HSLA steel (high strength low alloy) Tool steel (very hard; heat-treated)
Other Iron-based materials
Cast iron (>2.1% carbon) Wrought iron (almost no carbon) Ductile iron

Chromoly is an abbreviation for "chromium-molybdenum steel". 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, and is 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.

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