What Makes Tool Steel So Tough?

Behind tungsten, steel is considered one of the toughest metals in the world, making it a perfect material for tools and heavy duty parts that are put through repeated service. However, not all steels are created equal when it comes to toughness. To understand what makes some steel so tough, it’s important to delve into the difference and relationship between wear resistance and toughness.

Wear Resistance vs. Toughness

Wear resistance refers to a material’s ability to withstand abrasion and erosion, particularly when in contact with other surfaces. Toughness, on the other hand, is a measure of a material’s ability to absorb energy and deform plastically without fracturing. These two properties are essential when it comes to tool steels, as they are subjected to intense mechanical forces during their use.

The relationship between wear resistance and toughness is a trade-off. As the wear resistance of the steel increases, its toughness decreases. This trade-off occurs due to the microstructural changes that take place in the steel when attempting to enhance one property at the expense of the other.

Let’s take a closer look at different types of tool steels to understand this relationship better.

Common Tools Steels in Heat Treating and Beyond

Among the most commonly heat-treated tool steels, two stand out for their exceptional toughness: S7 and H13. These steels possess remarkable strength and durability, making them ideal for demanding applications. They strike a balance between wear resistance and toughness, offering reliability even under harsh conditions.

On the other hand, steels like A2 and D2 exhibit very good wear resistance but are not as tough as S7 and H13. The difference lies in their carbon content, with A2 and D2 containing significantly more carbon (around 2%). Higher carbon content leads to the formation of carbide within the steel’s matrix, which enhances wear resistance and decreases toughness.

Carbon is the Key

Carbon content plays a crucial role in determining the toughness of tool steels. S7 and H13, with their lower carbon content below 0.77%, possess good toughness because they do not have an excessive amount of carbide within their matrix. This composition allows them to maintain a balance between wear resistance and toughness, making them reliable choices for a wide range of tooling applications.

More Episodes to Check Out

Check out Metallurgy Minute 004: How cooling effects carbide in steel  and Metallurgy Minute 001: How can steel be used to cut steel? to learn more about heat treating steel.