Seamless steel pipe is a metal material with a yield phenomenon. The stress at which the sample can continue to elong without increasing the force during the stretching process is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
The upper yield point (σsu) of the seamless steel pipe: the maximum stress before the sample yields and the force drops for the first time;
the lower yield point (σsl): the minimum stress in the yield stage when the initial transient effect is not taken into account.
The calculation formula of the yield point of seamless steel pipe is:
In the formula: Fs--yield force (constant) during the tensile process of the specimen, N (Newton) So--the original cross-sectional area of the specimen, mm2.
Elongation of seamless steel pipe after breaking (σ)
In the tensile test, the percentage of the length of the gauge length increased after the sample is broken to the original gauge length is called the elongation. Expressed by σ, the unit is %. The calculation formula is:
In the formula: L1-the gauge length of the specimen after it is broken, mm; L0-the original gauge length of the specimen, in mm.
Reduction of area of seamless steel pipe (ψ)
In the tensile test, the percentage of the maximum reduction of the cross-sectional area at the reduced diameter of the sample after the sample is broken to the original cross-sectional area is called the reduction of area. Expressed in ψ, the unit is %.
In the formula: S0-the original cross-sectional area of the sample, mm2; S1-the minimum cross-sectional area at the reduced diameter of the sample after it is broken, mm2.
