Alloy Steel vs. Carbon Steel Bars: What’s the Difference?

It is why you will typically see an alloy grade used in the frame of an airplane or the structure of an oil well and a carbon grade in construction equipment or automotive parts. But why? Let’s dig into the chemical makeup of these two products.

What is the Difference Between Carbon Steel and Alloy Steel?

Carbon steel contains mostly iron and carbon (less than 2%) as its primary alloying elements, while alloy steel contains such elements as manganese, nickel, chromium, vanadium, and molybdenum, among others.

These additional elements help improve the strength, hardness, hardenability, and toughness of alloy steel. This makes it ideal for use in more high-performance applications like those in aerospace, defense, and oil and gas.

In addition, these elements also improve the corrosion resistance, heat resistance, and wear resistance of alloy steel.

Is Alloy Steel Stronger than Carbon Steel?

Alloy steel is stronger than carbon steel, due to various levels of manganese, nickel, chromium, vanadium, and molybdenum, contained within these steels.

The specific strength range depends on the specific composition of an alloy. The level of strength of alloy steel is further enhanced by the processing and heat treatment methods used on the material.

For example, thermal treatment of quench and tempering can be applied to many alloy grades, which improves the strength of the material.

What are Some Common Alloy Grades?

4140/4150 are widely used alloy grades. They are considered to be the ultimate “general purpose” grades and are low in cost. The typical composition of these grades is roughly .95% chromium and .20% molybdenum.

A broad range of strength and toughness is attainable through variations in heat treatment. These grades also exhibit good hardenability, strength, wear resistance, toughness, and ductility.

In terms of fee-machining alloy bars, 41L40 is among the most common. This chrome-molybdenum alloy contains .40 carbon and .15/.35 lead. It can be quenched and tempered to a broad range of strength levels.

8620 is the most widely used of all case hardening alloys. Considered to be “general purpose” 8620 is low in cost and contains good properties. Its composition is well balanced, nominally .55% nickel, .50% chromium, .20% molybdenum.

4340 is a highly alloyed steel, nominally 1.80% nickel, .80% chromium, and .25% molybdenum, assuring deep hardness when quenched and tempered, with high strength characteristics attained throughout the section. This grade can be used for heavily stressed parts operating under heavy-duty conditions.