How to specify the yield point of 904L steel pipe? 1. 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 (σ Su): the stress before the yield of the specimen and the stress drop; the lower yield point (σ SL): the stress in the yield stage when the initial instantaneous effect is ignored. The calculation formula of yield point is as follows: FS is the yield stress (constant) in the tensile process of the sample, n (Newton) so -- the original cross-sectional area of the sample, mm2. Elongation after fracture (σ) in the tensile test, the percentage of the length increased by the gauge length to the original gauge length of the 904L stainless steel pipe sample after breaking is called the elongation. 2. Expressed by σ, the unit is%. The calculation formula of 904L stainless steel pipe is: L1 -- gauge length of sample after breaking, mm; l0 -- original gauge length of sample, mm. Reduction of area (ψ) in tensile test, the percentage of reduction of cross-sectional area at reduced diameter and original cross-sectional area of sample after breaking is called reduction of area. Represented by ψ, the unit is%. The calculation formula is as follows: S0 is the original cross-sectional area of the sample; S1 is the cross-sectional area of the reduced diameter after breaking.