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Mechanical properties of steel

2016-07-18 18:00:43   COMMENT:0 HITS:
Mechanical properties of steel is an important index to ensure the final performance of the steel (mechanical properties), it depends on the chemical composition and heat treatment system. In the steel tube standard, according to the different requirements, the provisions of the tensile properties (tensile strength, yield strength or yield point elongation) and hardness, toughness index and user requirements of high and low temperature performance.
  The tensile strength (b)
  Specimen in the tensile process and the rupture under the maximum force (FB) and samples divided by the original cross-sectional area (S0) income should stress (sigma), known as the tensile strength (o b), the unit is n / mm2 (MPA). It indicates the maximum capacity of the metal material to resist damage under the action of tensile force.
  The yield point (s)
  With the yield phenomenon of the metal material, the specimen in the process of tension does not increase (keep constant) can continue to stretch the stress, said the yield point. If the force is decreased, the upper and lower yield points should be distinguished. The yield point of the unit is N/mm2 (MPa).
   Upper yield point (sigma Su): samples yield and force declined for the first time before the maximum stress; yield point (sigma SL): when regardless of the initial transient effect, yield stage in the minimum stress.
  The formula for calculating the yield point is:
 Fs-- (Heng Ding), N (Newton) So-- specimens of the original cross section area, mm2.
 The elongation (sigma)
 In a tensile test specimen, the percentage of breaking from the standard after the increase in the length of the original gauge length, called elongation. The sigma said unit for%. Formula: sigma = (Lh-Lo) /L0*100%
  Type: Lh-- samples were broken after the gauge length, mm; L0-- sample original gauge length, mm.
  The contraction ratio of section (I)
  In the tensile test, the specimen fractured the shrink diameter cross-sectional area of the biggest shrinkage percentage of reduction and the original cross-sectional area, known as the section shrinkage. The PSI said unit for%. The calculation formula is as follows:
  Type: S0-- samples of the original cross-sectional area, mm2; S1-- samples were broken after shrinkage minimum cross-sectional area diameter, mm2.
  The hardness index
  The ability of a metal material to resist a hard object on the surface of a hard object. According to the test method and the scope of application is different, the hardness can be divided into the hardness of the hardness, hardness, Vivtorinox hardness, shore hardness, micro hardness and high temperature hardness, etc.. In general, there are three kinds of tubes, which are commonly used in the tube, which are the hardness of the.
  A, hardness (HB)
  With a certain diameter of steel ball of the ball or hard alloy, the provisions of the test force (f) is pressed into the pattern surface, the provisions to keep time after unloading test force, and the measurement of the surface of the sample indentation diameter (L). The hardness value is obtained by dividing the test force by the surface area of the indentation. To HBS (steel ball) said that the unit is N/mm2 (MPa).
  Its formula is:
  F-- press into the surface of the metal test force, N; D-- test with a steel ball diameter, mm; d-- indentation average diameter, mm.
  Determination of the hardness is more accurate and reliable, but generally HBS only applicable to 450N/mm2 (MPa) of the following metal materials, for the hard steel or thin sheet does not apply. In the standard of steel pipe, the most widely used, the indentation diameter D is often used to indicate the hardness of the material, both intuitive and convenient.
   For example: 120HBS10/1000/30: (10mm) with the diameter of the steel ball in the 1000Kgf (9.807KN) test force, to maintain 30s (SEC) measured the hardness of the measured value of mm2 120N/ (MPa).

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