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.


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