Physical properties of steel

　　Physical properties of steel:

　　The mechanical properties of steel are important indicators to ensure the ultimate usability (mechanical properties) of steel, which depend on the chemical composition and heat treatment system of the steel. In steel pipe standards, tensile properties (tensile strength, yield strength, yield point, elongation), hardness, toughness indicators, as well as high and low temperature properties required by users are specified according to different usage requirements

　　D tensile strength (ob)

　　The maximum force (Fb) that the specimen bears during the tensile process at break (the stress (o) obtained from the original cross-sectional area (So) of the specimen is called the tensile strength (b). The unit is N/mm2 (MPa). It represents the maximum resistance of the metal material to failure under tensile force. The calculation formula is:

　　In the formula: Fb - the maximum force borne by the specimen during fracture, N (Newton); So - Original cross-sectional area of the sample, mm2

　　@Yield point (os)

　　The stress at which a metal material with yield phenomenon can continue to elongate without increasing (maintaining a constant) force during the tensile process is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is/mm2 (MPa)

　　Upper yield point (OSU): The maximum stress of the specimen before yielding and the first decrease in force; Lower yield point (osl): The minimum stress in the yield stage when the initial instantaneous effect is not considered.

　　The formula for calculating the yield point is:

　　In the formula: Fs - yield force during the tensile process of the specimen (constant) N (Newton) S - original cross-sectional area of the specimen, mm2

　　Elongation after 3 fractures (o)

　　In a tensile test, the percentage of the increase in gauge length of the specimen after fracture compared to the original gauge length is called elongation, expressed in o, and expressed in%. The calculation formula is:

　　In the formula: L1- gauge length of the sample after fracture, mm; LO - Original gauge length of the sample, mm.

　　O section yield ()

　　In a tensile test, the maximum reduction in cross-sectional area at the reduced diameter of the specimen after breaking is called the percentage of the original cross-sectional area, which is called the reduction in area. Expressed in%. The calculation formula is as follows:

　　In the formula, SO - the original cross-sectional area of the sample, mm2; S1- Minimum cross-sectional area at the reduced diameter of the specimen after fracture, mm2

　　G indicator

　　The ability of metal materials to resist surface indentation by hard objects is called hardness. According to the test method and scope of application, the hardness can be divided into Brinell hardness hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high-temperature hardness. There are three commonly used types of hardness for pipes: Brinell, Rockwell, and Vickers.