Seamless steel pipe has become an indispensable part of people's lives. Seamless steel pipe is related to people's quality of life and promotes national finance. So what is the seamless steel tube in the end?
Mechanical properties of steel is an important index to ensure the ultimate performance of steel, which depends on the chemical composition of steel and heat treatment system. In the standard of steel pipe, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness index, and high and low temperature properties required by the user are stipulated in the standard of steel pipe.
Tensile strength (sigma B)
In the tensile process, the maximum force (Fb), divided by the original cross section area (So) of the sample (sigma), is called tensile strength (sigma B), and the unit is N/mm2 (MPa). It represents the maximum ability of metal materials to resist failure under tensile force.
(2) yield point (sigma S)
The yield point is the stress at which the tensile force of the specimen can continue to elongate without increasing (keeping constant) during the tensile process. 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 (sigma Su): the maximum stress before the first drop in the yield of the specimen; the lower yield point (sigma SL): the minimum stress in the yield phase when the initial instantaneous effect is not counted.
The formula for calculating the yield point is:
Formula: the yield force (constant) during the tensile test of Fs-- specimen, and the original cross section area of N (Newton) So-- sample, mm2.
The elongation at post fracture (sigma)
In tensile tests, the percentage of the increase in the distance between the specimen and the original standard distance after elongation is called elongation. It is expressed in sigma, and the unit is%. The calculation formula is: _=(Lh-Lo)/L0*100% formula: Lh--the length of standard distance after tensile fracture, mm; L0--the length of original standard distance, mm.
Cross section shrinkage rate
In the tensile test, the maximum reduction of the cross-sectional area at the shrinkage of the specimen after tensile fracture is the percentage of the original cross-sectional area, which is called the section shrinkage. The unit is per percent. The calculation formula is as follows:
Type: the original cross-sectional area of S0-- specimen, mm2, S1--, and the minimum cross section area of the specimen at the reduced diameter, mm2.
The ability of metal materials to resist hard surfaces is called hardness. The hardness can be divided into Brinell hardness, Rockwell hardness, Vivtorinox hardness, Shaoshi hardness, microhardness and high temperature hardness, according to the different test method and application range. For pipes, there are usually three kinds of hardness, such as Brinell, Rockwell and Vivtorinox.
A, Brinell hardness (HB)
With a certain diameter steel ball or hard alloy ball, the prescribed test force (F) is pressed into the pattern surface, and the test force is removed after the time of maintenance, and the indentation diameter (L) on the surface of the specimen is measured. Brinell hardness is a quotient obtained by dividing the test force by the surface area of indentation. In HBS (steel ball), the unit is N/mm2 (MPa).
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