5140 Steel vs 4340 – What’s the Difference

5140 Steel VS 4340 Steel

When it comes to choosing the right type of steel for your project, you have a lot of options to consider. Two of the most popular types of steel are 5140 and 4340. Both of these alloys are excellent materials, but they have a few key differences you need to be aware of. This blog post’ll look at 5140 steel and 4340 steel. We’ll discuss their mechanical properties, uses, and everything you need to know.

What is 5140 Steel?

5140 steel is a low-alloy steel that contains chromium and molybdenum. This steel has excellent hardenability, making it an excellent choice for applications that require high tensile strength and resistance to wear and tear. This steel is commonly used to make gears, automotive parts, and machine components. It can be heat-treated to increase its hardness and durability. This steel has a low carbon content, making it ideal for applications where welding or machining is required.

What is 4340 Steel?

4340 steel is a high-strength alloy that contains chromium, nickel, and molybdenum. This steel is known for its toughness and high tensile strength. It is commonly used in applications that require high stress and fatigue resistance. This includes aircraft landing gear, crankshafts, and other high-performance parts. This steel is also heat-treatable, which makes it ideal for applications that require high durability and toughness.

Difference Between 5140 Steel and 4340 Steel

5140 steel is a low-alloy, chromium-manganese steel with good toughness and strength. It has excellent machinability and can be hardened through oil quenching. 4340 steel is made from a nickel-chromium-molybdenum alloyed grade of steel, which has high hardenability and good fatigue strength at relatively high strength levels. Both steels offer excellent wear resistance and mechanical properties, making them suitable for many applications in the automotive industry.

Chemical Composition

5140 steel is an alloy containing chromium, manganese, and molybdenum as strengthening agents. Its carbon content is 0.40–0.45%, making it a medium-carbon steel. 4340 steel is an alloy steel that contains nickel, chromium, and molybdenum as strengthening agents. It has a carbon content of 0.38–0.43%, which makes it low-carbon steel.

Mechanical Properties

Both 5140 and 4340 have excellent mechanical properties, but some differences exist. 5140 steel has a lower tensile strength compared to 4340 steel. However, 5140 steel is easier to machine and weld due to its lower carbon content. On the other hand, 4340 steel has a higher tensile strength and is more resistant to fatigue and wear. It is also more expensive and harder to machine compared to 5140 steel.


As mentioned earlier, 5140 steel is commonly used in the automotive industry, construction, and machine components. This steel is great for applications that require high wear resistance, toughness, and strength. It is also easier to machine and weld compared to other low-alloy steels. Meanwhile, 4340 steel is commonly used in high-performance applications that require extreme toughness and durability. This steel is ideal for aircraft landing gear, crankshafts, and other high-stress applications.


Choosing the right steel for your project depends on a lot of factors. You need to consider the application, the environment, and the type of stress the material will be subjected to. 5140 and 4340 steel are excellent materials, but they have different properties that make them ideal for certain applications. Knowing the differences between these two alloys will help you make an informed decision when choosing the right material for your project.