1. Yield point (σ S)
When the steel or sample is stretched, when the stress exceeds the elastic limit and the steel or sample continues to undergo obvious plastic deformation even though the stress does not increase anymore, this phenomenon is called yield, and the minimum stress value when yielding phenomenon is the yield point. If Ps is the external force at the yield point s and Fo is the fracture area of the sample, then the yield point σ s =Ps/Fo(MPa), MPa is called MPa equal to N (Newton) /mm2, (MPa =106Pa, Pa: PASCAL =N/m2)
2. Yield strength (σ 0.2)
The yield point of some metal materials is not obvious and it is difficult to measure. Therefore, in order to measure the yield characteristics of materials, the stress at which the permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length) is defined as the conditional yield strength or yield strength σ 0.2 for short.
3. Tensile strength (σ B)
The maximum stress is reached by a material during tensile stretching from the beginning until a fracture occurs. It shows how much steel resists breaking. The corresponding tensile strength and compressive strength, bending strength, etc.
If Pb is the maximum tensile force of the material before it is broken and Fo is the cross-section area of the sample, then the tensile strength σ b= Pb/Fo (MPa).
4. Elongation (δ S)
After the material is broken, the plastic elongation of the length and the percentage of the original specimen length is called elongation or elongation.
5. Compressive strength ratio (σ S / σ B)
The ratio of the yield point (yield strength) of steel to the tensile strength is called the yield strength ratio. The greater the compressive strength ratio, the higher the reliability of structural parts, the general carbon steel compressive strength ratio is 0.6-0.65, low alloy structural steel is 0.65-0.75 alloy structural steel is 0.84-0.86.
6. The hardness
Hardness is the ability of a material to resist hard objects pressing on its surface. It is one of the important performance indexes of metal materials. General hardness is taller, and wear resistance had jumped over. Commonly used hardness indicators are Brinell hardness, Rockwell hardness, and Vickers hardness.
⑴ Brinell hardness (HB)
With a certain load (generally 3000kg), the hardened steel ball of a certain size (generally 10mm in diameter) is pressed into the surface of the material and kept for a period of time. After the load is removed, the ratio of the load and the indentation area is the Brinell hardness value (HB), and the unit is kg force /mm2 (N/mm2).
⑵ Rockwell hardness (HR)
When HB> 450 or the sample is too small, the Brinell hardness test can not be used instead of the Rockwell hardness measurement. It is to use a diamond cone with a top Angle of 120 ° or a steel ball with a diameter of 1.59 or 3.18mm to press into the surface of the measured material under a certain load, and the hardness of the material can be calculated by the depth of the indentation. The hardness of the test material, it is divided into three different scales:
HRA: Hardness obtained with a 60kg load and a diamond cone press for extremely hard materials such as hard alloys.
HRB: the hardness is obtained by using a 100kg load and a 1.58mm diameter hardened steel ball, used for low hardness materials (such as annealed steel, cast iron, etc.).
HRC: hardness obtained by 150kg load and drill cone press for very hard materials such as hardened steel.
⑶ Vickers hardness (HV)
With a load of less than 120kg and a tip Angle of 136 °, the diamond square cone indenter is pressed into the surface of the material, and the surface area of the material indentation pit is divided by the load value, which is the Vickers hardness value (HV).
