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The OnlineMetals Guide to (chromoly) Alloy Steel 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. Chromoly contains chromium but it does not have the corrosion resistance of stainless steel. 8620 is a triple-alloy carburizing steel with good toughness and ductility, increased hardness penetration, and hardneability to a strong, tough, core, with high case-hardness. Weldability is rated as excellent. 4130 (chromoly) Alloy Steel (available in Round, Sheet, Tube) 4340 (chromoly) Alloy Steel (available in Round) 8620 (chromoly) Alloy Steel (available in Round) 4130 (Chromoly) Normalized Alloy Steel Minimum Properties Ultimate Tensile Strength, psi 97,200 Yield Strength, psi 63,100 Elongation 25.5% Rockwell Hardness B92   4130 (Chromoly) Annealed Alloy Steel Minimum Properties Tensile Strength, psi 81,200 Yield Strength, psi 52,200 Elongation 28.2% Rockwell Hardness B82 Chemistry Iron (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 (chromoly) Normalized Alloy Steel Minimum Properties Ultimate Tensile Strength, psi 186,000 Yield Strength, psi 125,000 Elongation 12.2% Rockwell Hardness B100 Chemistry Iron (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 Properties Tensile Strength, psi 97,000 Yield, psi 57,000 Brinell Hardness 201 Elongation 25% Machinability 66% Chemistry Carbon (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 At OnlineMetals, we all failed shop class. Multiple times. As a matter of fact, our employment applications specifically ask to see people's grades for their high school shop classes. If they're too high, they go into the rejected pile. We're also not engineers, and cannot make any specific recommendations about the suitability of a given alloy, temper, or shape for your project or application. 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. This ends the part of the website that our pointy-headed lawyers made us put in.