Hainan Steel Supermarket
1. Yield point（ σ S)
When the stress of a steel or specimen exceeds the elastic limit during tension, even if the stress no longer increases, the steel or specimen continues to undergo significant plastic deformation, which is called yield. The minimum stress value at which yield occurs is the yield point. If Ps is the external force at the yield point s and Fo is the cross-sectional area of the specimen, then the yield point σ S=Ps/Fo (MPa).
2. Yield strength（ σ 0.2)
The yield point of some metal materials is extremely unclear and difficult to measure. Therefore, in order to measure the yield characteristics of the material, it is specified that the stress at which permanent residual plastic deformation occurs is equal to a certain value (usually 0.2% of the original length), which is called the conditional yield strength or simply the yield strength σ 0.2.
3. Tensile strength（ σ B)
The maximum stress value that a material reaches from the beginning to the point of fracture during the stretching process. It represents the ability of steel to resist fracture. Corresponding to tensile strength are compressive strength, flexural strength, etc. If Pb is the maximum tensile force reached before the material is pulled apart, and Fo is the cross-sectional area of the specimen, then the tensile strength σ B=Pb/Fo (MPa).
4. Elongation rate（ δ S)
The percentage of plastic elongation of a material after breaking compared to the length of the original specimen is called elongation or elongation.
5. Bending strength ratio（ σ S/ σ B)
The ratio of the yield point (yield strength) of steel to its tensile strength is called the yield strength ratio. The greater the yield to strength ratio, the higher the reliability of structural components. Generally, the yield to strength ratio of carbon steel is 0.6-0.65, while that of low alloy structural steel is 0.65-0.75. Alloy structural steel is 0.84-0.86.
6. Hardness
Hardness represents the ability of a material to resist hard objects pressing into its surface. It is one of the important performance indicators of metal materials. The higher the hardness, the better the wear resistance. The commonly used hardness indicators include Brinell hardness, Rockwell hardness, and Vickers hardness.
1) Brinell hardness (HB)
Press a hardened steel ball of a certain size (usually 10mm in diameter) into the surface of the material under a certain load (usually 3000kg), maintain it for a period of time, and after unloading, the ratio of the load to the indentation area is the Brinell hardness value (HB).
2) Rockwell hardness (HR)
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and Rockwell hardness measurement should be used instead. It is a diamond cone with a top angle of 120 ° or a steel ball with a diameter of 1.59 and 3.18mm, pressed into the surface of the tested material under a certain load, and the hardness of the material is calculated from the depth of the indentation. According to the different hardness of the test materials, there are three different scales to represent:
HRA:It is a hardness obtained using a 60kg load and a diamond cone indenter, used for materials with extremely high hardness (such as hard alloys).
HRB:It is the hardness obtained using a 100kg load and a 1.58mm diameter quenched steel ball, used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC:It is a hardness obtained using a 150kg load and a diamond cone indenter, used for materials with high hardness (such as quenched steel).
3) Vickers hardness (HV)
The Vickers hardness value (HV) is obtained by pressing a diamond square cone indenter with a load of up to 120kg and a top angle of 136 ° into the surface of the material, and dividing the surface product of the material indentation by the load value.
