Steel strength is a complex attribute, encompassing several mechanical properties that together determine the material's resistance to external forces and stresses. Understanding it requires evaluating a range of factors, from tensile/yield/shear/compressive strength to environmental conditions.
What Is Steel Strength?
Steel strength is a general phrase that cannot be precisely quantified. It is best defined as follows and includes a number of distinct mechanical property features of steel:
Steel strength is the culmination of all mechanical behaviors that result in an overall resistance to stresses, pressures, and energies from the environment before breaking or irreversible deformation takes place.
For more information on mechanical properties, visit our Introduction to Mechanical Properties of Metals.
Types of Mechanical Steel Strength
Fundamentally, the strength of steel may be divided into four distinct metrics, each of which is the steel's breaking point under the specific force or stress applied to it. To create a collective observation, each of the four forms of strength should be seen separately and in conjunction with one another.
Tensile Strength: Steel's ability to resist being pulled apart (also known as ultimate tensile strength).
Tensile Stress: Pulls materials in opposite directions.
Yield Strength: The point at which a metal's elastic behavior gives way to plastic deformation.
Elasticity: A material's ability to bounce back to its original shape after experiencing a deforming force.
Plastic Deformation: Point of permanent deformation (but not breakage).
Shear Strength: Steel's ability to resist breaking or slicing along its planes.
Shear Stress: Force that comes from the side, middle, or opposing directions, enacting itself on just a section of the metal, that could slice or break it.
Compressive Strength: Steel's ability to resist being squeezed, compressed, or reduced in size (not as relevant when evaluating steel fasteners).
Compressive Stress: Force that pushes steel together to shorten it and spread it in a lateral direction.
These strengths will all have an impact on one another. Tensile strength influences yield and shear strength, compressive strength influences yield strength, and so on. It's critical to avoid assessing them in a vacuum. Since most other metrics are derived from tensile strength, it is ultimately advantageous to start there.
Other Mechanical Properties That Influence Strength
A metal can be strong without being very hard if its tensile, yield, shear, and compressive strengths are taken into account. This is where the steel's strength is affected by its hardness and ductility.
Hardness
The relationship between hardness and strength is complex, especially because they measure similar things:
Strength measures resistance to outside forces and stresses.
Hardness measures the ability to resist plastic deformation.
The same concept is being tested across a wide range of hardness tests: how much power is required to press an object into a material and leave a lasting indentation? It would seem that a metal's resistance to an external force increases with its hardness, signifying its strength. In actuality, greater hardness tends to be correlated with higher tensile and yield strengths.
The steel must, however, withstand additional forces, such as cracking. An extremely hard steel can become so brittle that it breaks readily, marking the threshold at which strength is no longer an advantage. In fact, too much hardness can weaken steel.
Ductility
This is also a hard relationship to quantify, so we'll start with a definition:
Ductility: The measure of a metal's ability to undergo plastic deformation without breaking.
Ductility is measured by two tests:
Elongation: Measures how far a material stretches before breaking. The test marks two points on the material before it is stretched. Once it is stretched to its breaking point, the points are measured again, and the elongation is calculated by the two distances.
Reduction of Area: Measures how much the area reduces from its starting point to its breaking point. The test measures the diameter of the material before stretching and after breaking and calculates the difference.
One way to look at ductile steel's low tensile and yield strength is to see how little it resists plastic deformation. But because it is difficult to break something that bends readily, it probably has a lesser shear strength. Once it has warped, though, it is flexible and resists splitting.
Machineability
Machinability is the degree to which a material may be cut with little to no chipping or deterioration of the surface quality. A poor machineability material would need more force and probably result in damage, whereas a high machineability material can be cut simply and with little resistance.
Reduced tensile strength is typically associated with good machinability; compare the difficulty of cutting putty with baked clay. The link with shear strength is the same: a material is easily broken along its planes if it can be machined.
Toughness
Tensile strength and ductility are two characteristics that together make up toughness. A material is considered tough if it has both qualities, that is, if it can only bend when subjected to a significant force while still resisting breaking. This is especially beneficial in cases where the metal is fatigued or damaged, as the ductility slows the rate at which tiny fissures break.
Tensile strength undoubtedly has a role in toughness. Tough steels frequently have high yield strengths as well because tensile and yield strength frequently cooperate. Another sign of a high shear strength would be the ability to withstand breaking under force.
Steel strength is a complex attribute that involves various mechanical properties determining its resistance to external forces and stresses. It is important to understand how it works so you can evaluate its potential performance in your application; Wenqi's Engineering Support Team helps you consider different strength factors so you can choose the right material for your needs.
