Guide To Chromoly Steel | Materials Talk Series

Chromoly Steel is the focus of our first "Materials Talk" video series! This type of cold roll steel is used in everything from bikes, to roll cages and rifle barrels. Chromoly is one of the most common and popular choices in steel types.
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Transcript:
Welcome to the Online Metals “Materials Talk” series
This video focuses on Chromoly, which is an abbreviation for chromium molybdenum steel, generally referred to as 41 series alloy steel.
Chromoly is a range of low alloy steels, commonly used in structures ranging from bicycle frames to flywheel components.
It offers the advantages of high tensile strength and malleability but cannot compete with its lightweight aluminum counterparts in terms of weight and provides less corrosion resistance than stainless steel.
In comparison to standard 1020 steel, Chromoly provides a considerably stronger and more durable product due to its higher yield strength. While it rates high in weldability, it should undergo pre and post weld thermal treatment to avoid cold cracking.
4130 is an alloy that is most commonly seen in structures for bicycle frames and is required for certain racecar roll cages. This product can also be annealed, which softens the material and offers a more malleable form.
4150 is one of the materials accepted for use in M16 rifle and M4 carbine barrels by the United States military. Due to increased carbon content, this material is less prone to fatigue and failure for burst fire.
While Chromoly typically refers to material alloys in the 41 family, 8620 and 4340 alloys share many characteristics with the 41 series alloys.
8620 Chromoly is a triple alloy carburizing steel with good toughness and ductility. It also boasts increased hardness penetration and hardenability, giving it strong core with high case hardness. This means that it will have an excellent strength and durability, but the softer core prevents it from becoming brittle. Used for gears, shafts, and crank shafts.
4340 is a nickel chromium molybdenum alloy, a steel also known for its toughness and ability to attain high strengths in the heat-treated condition. It is good for highly stressed parts.
4340 and 4130 chromoly are both normalized alloy steel but have varying strengths hardness and chemistry.
4340 is commonly referred to as aircraft grade and is used in aircraft landing gear. It is offered in air melt and vacuum melt.
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