What is Alloy Steel?: Different Elements & Uses

Isn’t Steel an Alloy Already?

Yes, even “plain” steel is technically already an alloy primarily made of iron and carbon. However, alloy steel is used to describe steel compositions that include many more additional alloying elements beyond carbon and iron.

What is Alloy Steel?

Therefore, alloy steel is specifically a type of steel that incorporates more exotic alloying elements like chromium, phosphorus, molybdenum, or nickel. The objective of these tailored compositions is to adjust properties for different scenarios. For example, adding elements like vanadium or molybdenum to improve heat resistance for fire-prone buildings. Because of this, the name “alloy steel” ends up being fairly broad, focusing on the more complex chemical makeup of the steel rather than a specific composition or carbon content.

Alloy Steel vs. Carbon Steel

Speaking of carbon content, these levels are what classify carbon steel, compared to the alloying elements that give alloy steel its name. Carbon steel is generally more affordable and machinable, while alloy steel’s specialization makes it more expensive but also less brittle, more wear-resistant, and tougher.

Alloy Steel vs. Stainless Steel

For those familiar with stainless steel, the inclusion of chromium may have stood out. However, stainless steel contains upwards of 10% of chromium compared to only a few percent in other alloy steels. As a result, this makes stainless steel more corrosion-resistant than alloy steel (unless composed specifically for that purpose). This is why you’ll often see stainless steel used in kitchenware, medical instruments, etc. while alloy steel is used more commonly in industrial equipment and structural applications.

Alloy Steel Properties

Alloy steel’s versatility makes it incredibly valuable for complex projects that need specific characteristics to ensure long-term success. Whether adding chromium for better corrosion resistance or manganese for higher tensile strength, alloy steel provides incredible adaptability where traditional carbon steel isn’t enough.

Alloy Steel Composition

Low alloy steel contains higher percentages of carbon and iron (with lower amounts of additional alloying elements), while high alloy steel is made from a greater percentage of elements like chromium or nickel. A low alloy steel like 4140 is composed of:

• Carbon: 0.38%-0.43%
• Iron: ~97% (primary component)
• Chromium: Improves corrosion and wear resistance
• Molybdenum: Bolsters high-temperature strength
• Manganese: Contributes to better machinability

Because of their cost, high alloy steel is typically used in smaller applications like tools, such as M2 high speed steel used for drills and lathes:

• Carbon: 0.78%-0.88%
• Iron: ~80% (primary component)
• Tungsten: 5.5%-6.75%
• Molybdenum: 4.5%-5.5%
• Chromium: 3.75%-4.5%
• Vanadium: 1.75%-2.2%
• Nickel: 0.3%
• Silicon: 0.2%-0.45%
• Manganese: 0.15%-0.88%

Density of Alloy Steel

The density of alloy steel is highly dependent on its chemical composition. However, densities are usually between 0.27 and 0.29 lb/in³ with low alloy steel being higher in this range because they contain higher amounts of iron (which is a relatively dense metal). This is usually coupled with higher-than-average strength, toughness, or corrosion resistance depending on the makeup of the steel grade.

Weight of Alloy Steel

Weight depends on the size of an object, so you’ll need to measure its size and know the alloy grade’s density. To calculate the weight of an alloy steel product, use this formula:

Weight = Volume x Density

For example, an M2 high speed steel (0.294 lb/in³) piece that’s 2” x 2” x 4” (16 in³) would weigh about 4.7 lbs (0.294 * 16).

Alloy Steel Melting Point

Similar to density, the melting point will heavily rely on the composition of each alloy steel — 4140 alloy steel’s melting point is 2,580°F, while M2 steel’s melting point is significantly lower between 2,170°F and 2,250°F. Other alloy steel grades like H13 tool steel are designed to be hotter (2,600°F) for high-heat applications.

How is Alloy Steel Made?

Like other steels, alloy steel manufacturing begins with the procurement of iron, either through mining or recycling. Additional alloying elements are selected based on desired properties — chromium for corrosion resistance, manganese for toughness, molybdenum for heat resistance, etc. From there, raw iron is melted in an electric arc furnace with temperatures reaching more than 2,900°F. Refinement processes like Argon Oxygen Decarburization are used to remove impurities such as excess carbon or sulfur.

Alloying elements are also added through these steps, but the timing depends on the element. For example, manganese and chromium are added during the melting process because they’re integral to the formation of the steel matrix. Other elements like nickel and molybdenum are added later during the refining process to prevent losses during melting.

Further refinement processes like vacuum degassing or electroslag remelting may be employed to further enhance the final product. From there, the alloy steel can be cast into slabs, ingots, billets, and more before being rolled/forged and heat treated.

Alloy Steel Applications

Common uses for alloy steel include:

• Structural components: Beams, columns, and other framing components for buildings can use alloy steel for its strength and toughness.
• Automotive engine parts: In order to handle high temperatures and high stresses, crankshafts, camshafts, and more may use chromium-molybdenum steels.
• Gears and bearings: For similar reasons, gears and bearings that need to resist wear and prevent fatigue use tough alloy steel grades.
• Aircraft frames: Aircraft undergo intense loads and stress, so their frames can’t be brittle — low alloy steels that are more ductile can be incorporated here.
• Pipelines and oil storage tanks: Corrosive chemicals and high temperatures require resistant steels like those using high percentages of chromium and molybdenum.
• Drilling tools: High speed alloys like M2 are incredibly valuable for parts that experience extreme friction heat and wear, adding elements like vanadium.
• Railroad tracks: Another use that needs to resist continuous wear is infrastructure like rails, using manganese to prevent deterioration from decades of use.
• Surgical instruments: Certain high-end stainless steels are used for scalpels and orthopedic implants like joint replacements because corrosion can lead to infection.

Need High-Quality Steel Designed to Meet Specific Needs?

Alloy steel (especially high alloy steel) is typically not necessary for structural projects. However, it’s important to understand the flexibility of steel and how working with the right suppliers can get you cost-effective metal that suits your requirements. For example, our focus is on carbon steel for structural applications but we also carry a number of more niche steel grades that may be more tailored to the characteristics you need. Contact a sales representative today to see if we can supply the steel for your next project.