### Pure iron and carbon steel (how to distinguish between carbon steel and iron)

1. Mechanical properties of steel 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 still continues to undergo obvious plastic deformation. This phenomenon is called Yield, and the minimum stress value when the yield phenomenon 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 sample, then the yield point σs =Ps/Fo(MPa). 2. Yield strength (σ0.2) The yield point of some metal materials is very inconspicuous and difficult to measure. Therefore, in order to measure the yield characteristics of the material, it is stipulated that the permanent residual plastic deformation is equal to a certain value (generally 0.2 of the original length %) is 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 fracture during the stretching process. It represents the ability of steel to resist fracture. Corresponding to tensile strength are compressive strength, flexural strength, etc. Let Pb be the maximum tensile force reached before the material is broken, and Fo be the cross-sectional area of the sample, then the tensile strength σb= P

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