The stress at which a seamless steel pipe, a metal material with a yield phenomenon, can continue to expand without increasing force (maintaining stability) during the stretching process, is called the yield point. If the force decreases, it is necessary to distinguish between the upper and lower yield points. The unit of yield point is N/mm2 (MPa).
Yield point on seamless steel pipe（ σ Su): ******** stress before the first decrease in force due to yield of the sample; Lower yield point（ σ SL): The minimum stress in the yield stage when the original instantaneous utility is not taken into account.
The calculation formula for the yield point of seamless steel pipes is:
In the formula: Fs - the appropriate force (stable) during the stretching process of the sample, N (Newton) So - the initial cross-sectional area of the sample, mm2.
Elongation after fracture of seamless steel pipes（ σ)
In a tensile experiment, the percentage of the length of the gauge length increased by the specimen after breaking compared to the original gauge length is called the elongation. with σ Indicates that the unit is%. The calculation formula is:
In the formula: L1- gauge length of the sample after tearing, mm; L0- Initial gauge length of the sample, mm.
Reduction of section of seamless steel pipes（ ψ)
In tensile experiments, the main reduction in cross-sectional area at the reduced diameter of the specimen after tearing is called the percentage of the initial cross-sectional area, which is called the reduction in area. with ψ Indicates that the unit is%.
In the formula: S0- initial cross-sectional area of the sample, mm2; S1- The minimum cross-sectional area at the reduced diameter of the specimen after fracture, mm2.
