When testing the physical properties of steel, we mainly judge based on the test results of several indicators. These indicators include yield strength, tensile strength, elongation, hardness, yield point, and yield ratio.

1. Yield point (σs)

When the steel or sample is stretched, when the stress exceeds the elastic limit, even if the stress no longer increases, the steel or sample continues to undergo significant plastic deformation. This phenomenon is called yielding, and the minimum stress value when yielding occurs is for the yield point. Assume Ps is the external force at the yield point s, Fo is the cross-sectional area of the sample, then the yield point σs =Ps/Fo(MPa)

2. Yield strength (σ0.2)

The yield point of some metal materials is extremely unclear and difficult to measure. Therefore, to measure the yield characteristics of the material, the stress when the permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length) is specified, which is called the condition. Yield strength or simply yield strength σ0.2.

3. Tensile strength (σb)

The maximum stress value reached by the material from the beginning to the time of fracture during the stretching process. It indicates the steel's ability to resist fracture. Corresponding to tensile strength are compressive strength, flexural strength, etc. Assuming that Pb is the maximum tensile force reached before the material is broken, Fo is the cross-sectional area of the sample, then the tensile strength σb = Pb/Fo (MPa).

4. Elongation (δs)

After the material is pulled apart, the percentage of its plastic elongation length to the original sample length is called elongation or elongation.

5. Yield-strength ratio (σs/σb)

The ratio of the yield point (yield strength) of steel to its tensile strength is called the yield ratio. The larger the yield-strength ratio, the higher the reliability of structural parts. Generally, the yield-strength ratio of carbon steel is 0.6-0.65, and that of low-alloy structural steel is 0.65-0.75. Alloy structural steel is 0.84-0.86.

6. Hardness

Hardness indicates a material's ability to resist hard objects pressing into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators include Brinell hardness, Rockwell hardness, and Vickers hardness.

When testing the physical properties of steel, we mainly judge based on the test results of several indicators. These indicators include yield strength, tensile strength, elongation, hardness, yield point, and yield ratio.

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