Do you really understand the mechanical properties of steel?
Time: 2025-09-12
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A Practical Guide to Key Performance Indicators
Steel is everywhere around us, in the homes we live in, the tools we use, the accessories we wear, the transportation we ride, and so on. It encompasses every aspect of our lives. Yet, it’s a familiar yet unfamiliar object. We’re familiar with its form and uses, but unfamiliar with its properties and production. Let’s gradually unveil the mysteries of steel, starting with understanding its mechanical properties.
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1、Mechanical properties of steel：Yield point (σs)
When stress exceeds the elastic limit during tension, steel or a specimen continues to undergo significant plastic deformation even when the stress stops increasing. This phenomenon is called yielding, and the minimum stress at which yielding occurs is the yield point. Let Ps be the external force at the yield point s, and Fo be the cross-sectional area of the specimen. Then, the yield point σs = Ps/Fo (MPa).
2、Mechanical properties of steel：Yield strength (σ0.2)
The yield point of some metal materials is extremely unclear and difficult to measure. Therefore, in order to measure the yield characteristics of the material, the stress at which permanent residual plastic deformation is equal to a certain value (generally 0.2% of the original length) is specified, which is called the conditional yield strength or simply the yield strength σ0.2.
3、Mechanical properties of steel：Tensile strength (σb)
The maximum stress reached during the tensile process, from the beginning to the point of fracture. It indicates the steel’s ability to resist fracture. Corresponding to tensile strength are compressive strength, flexural strength, and other parameters. Let Pb be the maximum tensile force reached before the material breaks, and Fo be the cross-sectional area of the specimen. Then, tensile strength σb = Pb/Fo (MPa).
4、Mechanical properties of steel：Elongation (δs)
The percentage of the plastic elongation length of the material after it is broken to the original sample length is called elongation or extension.
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5、Mechanical properties of steel：Yield strength ratio (σs/σb)
The ratio of a steel’s yield point (yield strength) to its tensile strength is called the yield strength ratio. The larger the yield strength ratio, the more reliable the structural component. Generally, the yield strength ratio for carbon steel is 0.6-0.65, for low- alloy structural steel it ‘s 0.65-0.75, and for alloy structural steel it’s 0.84-0.86.
6、Mechanical properties of steel：Hardness
Hardness indicates a material’s ability to resist pressure from a hard object. It is one of the most important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indices include Brinell hardness , Rockwell hardness , and Vickers hardness .
(1) Brinell hardness (HB)
A hardened steel ball of a certain size (usually 10mm in diameter) is pressed into the surface of the material with a certain load (usually 3000kg) and kept for a period of time. After the load is removed, the ratio of the load to the indentation area is the Brinell hardness value (HB).
(2) Rockwell hardness (HR)
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness test should be used instead. It uses a diamond cone with a vertex angle of 120° or a steel ball with a diameter of 1.59 or 3.18 mm to press into the surface of the material under test under a certain load, and the hardness of the material is calculated from the depth of the indentation. According to the hardness of the test material, it is expressed in three different scales:
HRA: It is the hardness obtained by using a 60kg load and a diamond cone indenter, and is used for materials with extremely high hardness (such as cemented carbide, etc.).
HRB: The hardness is obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm. It is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: It is the hardness obtained using a 150kg load and a diamond cone indenter, and is used for materials with very high hardness (such as hardened steel, etc.).
(3) Vickers hardness (HV)
The Vickers hardness value (HV) is obtained by pressing a diamond square cone indenter with a load of less than 120 kg and a vertex angle of 136° into the material surface. The surface area of the indentation is divided by the load value.
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In summary, a deep understanding of steel’s core mechanical properties—yield strength, tensile strength, elongation, hardness, and yield-to-strength ratio—is the cornerstone of proper steel selection and application. These performance indicators collectively define whether a steel is suitable for your project and determine the safety, durability, and reliability of the final product.
Whether you’re looking for high strength, toughness, or superior wear resistance, choosing the right steel is crucial. Hopefully, this article will help you make a more informed decision for your next project.
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