4340 Steel vs S7 Steel – What’s the Difference

4340 Steel VS S7 Steel

The world of metallurgy is a fascinating one. For anyone working in industries that rely on steel for their operations, it’s always important to understand the differences between the various types of steel available. Among the many different types of steel, S7 and 4340 steel are among the most popular. They offer properties ideal for different applications, and understanding their differences is crucial for making the right choice. In this blog post, we will take a closer look at these two types of steel, their differences, and where they excel.

What is 4340 Steel?

Have you ever wondered what kind of metal goes into making high-performance automotive and aerospace parts? Look no further than 4340 steel. This alloy steel contains nickel, chromium, and molybdenum, making it incredibly tough and durable. Its high tensile strength and ability to withstand extreme temperatures make it a popular choice in manufacturing.

What is S7 Steel?

S7 steel is a high-carbon steel known for its strength and durability. It is a popular choice for tools and machinery parts due to its ability to withstand high impact and stress. S7 steel gets its name from its composition: it contains 7% chromium. This element provides a high level of toughness and hardness, making S7 steel ideal for applications requiring a sharp edge or high resistance to wear and tear.

Difference Between 4340 Steel and S7 Steel

4340 steel is a high-alloy Chromium-Molybdenum steel, and S7 steel is an extremely hard air or oil-hardened tool steel. 4340 has higher tensile strength, hardness, and much better fatigue strength than S7. However, S7 can be easily machined to close tolerances and has exceptional impact resistance even at subzero temperatures.


One of the key differences between S7 and 4340 steel is their composition. S7 is a shock-resistant tool steel that contains 0.45% carbon, 3.25% chromium, and 1.75% tungsten. It also has minor amounts of vanadium and molybdenum. 4340 steel, on the other hand, is a nickel-chromium-molybdenum alloy steel that contains 0.40% carbon, 0.80-1.10% chromium, 0.15-0.25% molybdenum, 1.65-2.00% nickel, and traces of sulfur and phosphorus. The chemical composition of these two steel types gives them their unique properties.


S7 steel has properties like high shock resistance, high wear resistance, and excellent toughness. Due to its composition, S7 is excellent for applications that require high-impact resistance, such as stamping dies, cold work tools, and shear blades. In contrast, 4340 steel has high toughness, flexibility, and strength. It has excellent fatigue resistance and is ideal for applications that require high strength and toughness, such as gears, pins, and aircraft landing gear.

Heat Treatment

S7 and 4340 steel require specific heat treatment processes to achieve their desired properties. S7 needs to be heated to 923°C to 954°C, quenched in oil, and then tempered at 177°C to 260°C. This process ensures that S7 steel has the proper shock and wear resistance properties. For 4340 steel, it needs to be soaked at 843°C, quenched in oil or water and then tempered at 149°C to 538°C. This heat treatment process hardens the steel and imparts high strength and toughness.


S7 and 4340 steel have different machinability properties, an important factor in certain industrial applications. S7 can be machined easily, but the tungsten in the steel can make the cutting tools wear out quickly. 4340 steel is hard to machine because of its high hardness and requires carbide tools to do the job correctly.


Finally, the cost is always a consideration when choosing between different types of steel. S7 is more expensive than 4340 steel because of its composition and the special heat treatment process it requires. However, S7 is a good investment for industrial operations requiring high shock and wear resistance.


In conclusion, if you are trying to choose between S7 and 4340 steel, it is essential to understand their differences and properties. Both are excellent choices for specific applications, and your choice will depend on your specific needs. S7 steel is perfect for high shock resistance applications, while 4340 steel is ideal for high strength and toughness applications.