Mechanical property index of the hottest seamless

2022-08-05
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Mechanical property index of seamless steel pipe

the mechanical property of steel is an important index to ensure the final service performance (mechanical property) of steel, which depends on the chemical composition and heat treatment system of steel. In the steel pipe standard, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indexes, as well as the high and low temperature properties required by users are specified according to different service requirements

① tensile strength( σ b)

the maximum force (FB) borne by the specimen during the tensile process, divided by the original cross-sectional area (so) of the specimen( σ), Called tensile strength( σ b) , in n/mm2 (MPA). It represents the maximum ability of metal materials to resist damage under tension

② yield to ensure the normal use point of the testing machine( σ s)

for metal materials with yield phenomenon, the stress when the specimen can continue to extend without increasing (maintaining constant) the force during the tensile process is called the yield point. If the force decreases, the upper and lower yield points shall be distinguished. The unit of yield point is n/mm2 (MPA)

upper yield point( σ Su): the maximum stress before the first decrease of the stress due to the yield of the sample; Lower yield point( σ SL): the minimum stress in the yield stage when the initial instantaneous effect is not considered

the calculation formula of yield point is:

where: FS - yield force (constant) during the tensile process of the sample, n (Newton) so - original cross-sectional area of the sample, mm2

③ elongation after fracture( σ)

in the tensile test, the percentage of the increased length of the gauge length of the specimen after breaking to the original gauge length is called the elongation. with σ Indicates that the unit is%. The calculation formula is: σ= (LH LO)/l0*100%

where: LH -- gauge length of the sample after breaking, mm; L0 -- original gauge length of sample, mm

④ for the former section, check the shrinkage( ψ)

in the tensile test, the percentage between the maximum reduction of the cross-sectional area at the reduced diameter and the original cross-sectional area after the specimen is broken is called the reduction of area. with ψ Indicates that the unit is%. The calculation formula is as follows:

where: S0 -- original cross-sectional area of the sample, mm2; S1 -- minimum cross-sectional area at the reduced diameter after fracture of the sample, mm2

⑤ hardness index

the ability of metal materials to resist the indentation surface of hard objects is called hardness. According to different test methods and application ranges, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, shore hardness, microhardness and high temperature hardness. There are three kinds of hardness commonly used for pipes: Brinell hardness, Rockwell hardness and Vickers hardness

a, Brinell hardness (HB)

use a steel ball or hard alloy ball with a certain diameter to press into the sample surface with the specified test force (f), remove the test force after the specified holding time, and measure the indentation diameter (L) on the sample surface. The Brinell hardness number is the quotient obtained by dividing the test force by the spherical surface area of the indentation. Expressed in HBS (steel ball), unit: n/mm2 (MPA)

its calculation formula is:

where: F - the test force pressed into the surface of the metal sample, N; D -- diameter of steel ball for test, mm; D-- average diameter of indentation, mm

the determination of Brinell hardness is accurate and reliable, but generally HBS is only applicable to metal materials below 450n/mm2 (MPA). It is not applicable to hard steel or thin tubular supports with different diameters and thicknesses that reduce metal embrittlement. In the steel pipe standards, Brinell hardness is the most widely used, and the indentation diameter D is often used to express the hardness of the material, which is intuitive and convenient

example: 120hbs10/1000/30: indicates that the Brinell hardness value measured by using a 10mm diameter steel ball under the action of 1000kgf (9.807kn) test force for 30s is 120n/mm2 (MPA)

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