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Sign In Chromoly - Chromium-Molybdenum Steel with more strength than mild steel
11/12/2024
Written by Dr. Juergen Abrams on November 12, 2024.
Chromoly steel is a low alloy steel which finds its uses in many different industries due to its high degree of strength and toughness.
The name Chromoly refers to the main alloying supplements Chromium and Molybdenum.
This steel group can be identified by the numbering 41xx like the 4140 steel, 4142, or the 4130.
Chromium-Molybdenum steel has more strength than mild steel, a higher tensile strength, and is easily hardened.
WHY IS IT CALLED CHROMOLY STEEL?
The term Chromoly is a combination of Chromium and Molybdenum, showing the main alloying elements of this kind of steel.
Chromium can increase corrosion resistance, though in these steel grades it is not high enough to make it a stainless steel grade.
Here it improves hardness penetration and toughness with a moderate corrosion resistance.
It enhances the heat-treatability of these steels for improved tensile strength and hardness without getting brittle.
Molybdenum increases strength at high temperatures and creep resistance.
It enhances hardenability and fatigue resistance as well as reducing the risk of cracking during welding.
This is due to the ability to resist the formation of carbides at the grain boundaries.
COMMON GRADES OF CHROMOLY STEELS
4140 / 4142 and 4140PH / 4142PH
The 4140 / 4142 and 4140PH / 4142PH are low alloy chromium molybdenum steels, also known as chromoly steel or chrome moly steel/CrMo-steel. They are heat-treatable steels which can be hardened fully through and to make the surface even harder, can be nitrided, depending which suits the application it is used for.
Due to its high toughness chromoly steel can be used to make flanges, crankshafts, clutch parts, connection rods, gears and bandages for example.
CHROMOLY VS. MILD STEEL PRICE DIFFERENCE
Mild steel, a non-alloyed steel, is compared to a chromoly steel, a low alloyed steel, on the lower end of the pay-scale. Any added alloy to the basic combination of iron and carbon adds extra costs. Alloy prices vary and depend on the amount that has to be used within a steel grade. So by adding Chromium and Molybdenum naturally adds extra costs.
The more alloys that are added or the higher the amount of one particular alloy will increase the costs of that steel grade and make some steels more expensive than others. Having chromium and molybdenum as an alloy in these steel grades gives it better toughness and durability making it usable in applications mild steel might not endure making the price difference justified.
KEY CHARACTERISTICS OF CHROMOLY STEEL:
Here are some key characteristics and uses of chromoly steel:
Characteristics
Strength to weight ratio and tensile strength:
Cromoly steel grades have a very high tensile strength, this means that less material can be used to make parts in comparison with other steels, for example mild steel. This can make parts lighter than when they were made from other steels.
Fatigue resistance:
It can withstand repeated stresses without cracking or fracturing. This means tools and parts made from these materials have a longer work life than if they are made from other steel like unalloyed or lower alloyed steels.
Heat treatability and wear resistance:
Chromoly is easily hardened by heat-treatment as well as work hardening. By nitriding these kinds of steels they can be surface hardened to give them an even harder surface for better wear resistance.
Hardness:
Due to its higher carbon and chromium content this steel group has a better hardness than mild steel and also has the ability to be nitrided to increase the surface hardness even more.
Toughness and shock resistance:
Chromoly steels have a high toughness which is a benefit for applications where high impact loads are applied to tools or parts made from this material.
Weldability:
In its annealed condition the weldability for chromoly steel is good. In its hardened condition the hardness these grades can achieve can be challenging though, cracking and breaking through thermal shock can be avoided by preheating the material evenly.
Uses
Automotive Industry:
Gears, crankshafts, axles have to withstand high mechanical stresses, chromoly steel can give high strength, fatigue resistance and wear resistance for these parts.
Aerospace Industry:
Landing gear components, engine parts or structural parts which require durability as well as high strength and heat resistance.
Oil and Gas Industry:
With good wear resistance , excellent toughness and moderate corrosion resistance chromoly steel can be used for drill collars, drill components or pressure valves in moderate corrosive environments.
Machinery:
Its wear resistance makes it ideal for gears, shafts and industrial equipment. Heavy duty equipment and machinery can handle heavy loads due to its strength and toughness and with the correct heat treatment hardness and toughness can be fine tuned for application requirements.
Mold and tool manufacturing:
Chromoly steel can, with the appropriate heat treatment, achieve a hardness which is needed for cutting tools. Its impact resistance makes it possible to absorb shocks and impacts that accrue during stamping for example.
Bicycle or Motorcycle Frames:
With a high strength to weight ratio and toughness, durable frames that can withstand impacts and fatigue, can be produced for bicycles and motorcycles.
Properties
Tensile Strength: Around 720 MPa.
Density: Approximately 7.85 g/cm³.
Melting Point: About 1415°C - depending on the carbon and alloy content.
Advantages
High strength: The combination of carbon, chromium and molybdenum makes it useful for applications which need to withstand heavy loads.
Hardenability: Easy to harden by heat treatment like quenching and tempering for advanced mechanical properties or for a harder surface it can be nitrided.
Cost-Effective: Economical for applications that need durability and fatigue strength.
Readily Available: Widely produced and available.
Sustainability: 100 % recyclable.
Repair and maintenance: With the correct expertise and techniques chromoly steel can be welded and machine repaired.
Disadvantages
Corrosion: Though it has some corrosion resistance it is not fully resistant to corrosion. Added protection and regular maintenance might be needed.
Prone to cracking: With improper thermal treatment this kind of material is prone to cracking, to reduce the possibility of cracking pre- and post heat treatment as well as controlled cooling rates can be required.
Weldability: With the correct preparation welding is possible but due to the high carbon content and hardenability complex. (see above “Prone to cracking”)
Workability: Heat treated and hardened this kind of steel becomes difficult to machine and might require specialized tools.
How to prevent corrosion of chromoly steel
To prevent corrosion and extend the lifespan and structural integrity of chromoly steel products they can be painted, galvanized, electroplated, oiled or passivated.On top of the former mentioned protections, regular maintenance and inspections can help spot potential weak points.
ABRAMS Industries® Chromoly steel
As a steel supplier with no minimum order quantity or value we have been supplying steel to a wide variety of industries and manufacturers in Germany since 2003, Europe since 2011 and now since 2020 across the U.S.A. and Canada.
We pride ourselves in supplying you with precision in tool steel, high speed steel, stainless steel, heat-treatable steel and case hardening steel in 44 steel grades with more than 53,000 dimensions.
As a chromoly steel supplier we saw, mill and grind for you in our Warehouse in Illinois.
Customized chromoly steel
Chromoly steel plates
Chromoly steel rods
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