Guide to the Different Types of Strength for Steel

May 3, 2022 | Categorized in: Properties

Steel is one of the strongest and most commonly used materials on the planet, but when we say that steel is “strong,” what does that actually mean? There are a number of different forces and situations that require different measurements of strength, so which ones are the most important to know?

Importance of using different strengths

Different steel products and different applications provide or require different forms of strength. For instance, strength against compression isn’t as important in a situation where the only forces acting on the steel are pulling outward. However, knowing the different types of strength and which grades or shapes of steel meet the requirements for a certain job is crucial for safety and reliability purposes.

Different types of strength measurements

“Strength” when referring to metals can refer to measuring resistance of a number of different forces. The most common strength measurements used in steel manufacturing are tensile, yield, and compressive strength. We’ll discuss these three, as well as some other examples that can be used to define a steel product’s characteristics.

Tensile strength

This measure of a material’s strength refers to its ability to resist tension, or forces pulling or stretching it apart. A material with low tensile strength would pull apart more easily than one with high tensile strength, such as steel. Applications like steel cables are a good representation of this strength, as these cables are usually under high levels of tension and need to resist this stress without breaking or stretching. A572-50, a steel grade that we frequently use for our structural shapes, has an ultimate tensile strength of over 70,000 psi (450 MPa).

Yield strength

Another common measure of a material’s strength is called yield strength, and is the amount of force that can be resisted before being permanently deformed. Essentially, this describes the maximum force that can be applied to deform a material, where it will still return to its original shape once the force is removed. Steel also has incredibly high yield strength, with another one of our common grades, A36, having a minimum yield strength of over 36,000 psi (250 MPa).

Compressive strength

The opposite of tensile strength, compressive strength measures how much a material can be squeezed together and reduced in size. This is often tested with a machine that applies an increasing load to the material until a certain amount of deformation or compression is reached. Materials such as concrete and ceramics tend to have very high compressive strength, but much lower tensile strength. Steel can not only match these materials’ compressive strength with a thinner profile, but also has very high tensile and yield strength.

Impact strength

As you might guess from the name, this type of strength measures a material’s ability to withstand a blow without breaking. It can also be thought of as the amount of energy that can be absorbed (without fracturing) when a sudden force is applied. Sometimes referred to as toughness, it’s most frequently measured by the Charpy impact test, which we discuss in more detail here.

Shear strength

This type of strength defines the resistance to unaligned forces pushing one part of the material in one direction, while another part of the material is pushed in the opposite direction. Shear force is how scissors cut, as a piece of paper is pushed down by one blade and up by another blade. Materials with high shear strength are difficult to cut with scissors and are more resistant to these opposing and parallel forces on an object.

Torsional strength

Defined as the resistance of torque, this measurement describes the ability of a material to withstand a twisting stress without rupturing. Hollow tubing (round, square, or rectangular) has incredibly high torsional resistance, while shapes such as beams have a comparatively lower torsional resistance and strength.

Corrosion resistance

While this might not seem like a measurement of physical strength that fits with the others, corrosion resistance is still a measure of how strong a material is against being worn away or deteriorated. This mostly occurs due to environmental factors like water or gases such as chlorine and ammonia. Galvanizing is a common process to increase steel’s corrosion resistance, and is covered in more depth here.

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