Mechanical properties of steel

 Mechanical properties of steel

　　1. Yield point (σs) When the steel or sample is stretched, when the load exceeds the elastic limit, even if the load is no longer increased, the steel or sample still continues to undergo significant plastic deformation, which is called yield. The minimum stress value at which the yield phenomenon occurs is the yield point. Let Fs be the external force at the yield point s, and S be the cross-sectional area of the sample, then the yield point σs = Fs/S(MPa), MPa is called MPa, which is equal to N (Newton)/mm2, (MPa=106Pa, Pa: Pascal =N/m2)

　　2. Yield strength (σ0.2) The yield point of some metal materials is very inconspicuous, and it is difficult to measure. Therefore, in order to measure the yield characteristics of the material, the permanent residual plastic deformation is equal to a certain value (usually the original length) 0.2%), called the conditional yield strength or yield strength σ0.2 for short.

　　3. Tensile strength (σb) is the maximum stress value reached by the material from the beginning to the time of cracking during the stretching process. It indicates the steel's ability to resist cracking. Corresponding to tensile strength are compressive strength, flexural strength, etc. Let Fb be the maximum tensile force reached before the material is broken, and S be the cross-sectional area of the sample, then the tensile strength σb= Fb/S (MPa).

　　4. Elongation (δs) After the material is broken, the percentage of its plastic elongation length and the original sample length is called elongation or elongation.

　　5. Yield ratio (σs/σb) The ratio of the yield point (yield strength) of the steel to the tensile strength is called the yield ratio. The greater the yield ratio, the higher the reliability of structural parts. Generally, the yield ratio of carbon steel is 0.6-0.65, that of low-alloy structural steel is 0.65-0.75, and that of alloy structural steel is 0.84-0.86.