1. Tensile strength (σb)
The stress (σ) obtained by dividing the original cross-sectional area (So) of the 45# steel pipe during the tensile process is called the tensile strength (σb) and the unit is N/mm2 (MPa). It represents the ability of 45# steel pipe to resist damage under tensile force.

2. Yield point (σs)
The stress of 45# steel pipe when the force does not increase (keep constant) during the stretching process can continue to elong, 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).

Upper Yield Point (σsu): The stress before the specimen yields and the force drops for the first time;
Lower Yield Point (σsl): The stress in the yield stage when the initial transient effect is not taken into account.

3. Elongation after fracture (σ)
In the tensile test of 45# steel pipe, the percentage of the length increased by gauge length and the original gauge length after the sample is broken is called elongation. Expressed in σ, the unit is %.

4. Reduction of area (ψ)
In the tensile test of 45# steel pipe, the percentage of the reduction of cross-sectional area at the reduced diameter and the original cross-sectional area of the sample after breaking is called the reduction of area. Represented by ψ, the unit is %.

5. Hardness index
The ability of 45# steel pipe to resist the indentation surface of hard objects is called hardness. According to different test methods and scope of application, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. There are three commonly used for 45# steel pipe: Brinell, Rockwell and Vickers hardness.