Introduction of mechanical properties of steel
1. yield point (sigma S)
Steel or under tensile, when the stress exceeds the elastic limit, even if the stress is not increased, and the sample of steel or continue to occur significant plastic deformation. This phenomenon is called the yield, and yield phenomenon by the minimum stress value is the yield point.
Let Ps be the external force at the yield point s, and the Fo is the section area of the specimen, then the yield point is s =Ps/Fo (MPa), and MPa is called MPa, equal to N (Newton) /mm2, (MPa=106Pa, Pa: Pascal, =N/m2)
2. yield strength (sigma 0.2)
The yield point of some metal material is not obvious, there are difficulties in measurement, so in order to measure the yield characteristics of materials, shall produce permanent residual plastic deformation is equal to a certain value (usually length 0.2%) stress, called conditional yield strength or yield strength 0.2.
3. tensile strength (sigma B)
The maximum stress at which the material reaches its fracture from the beginning to the end of the tension. It represents the magnitude of the steel's resistance to fracture. As well as tensile strength, there is also compressive strength, bending strength, etc..
Let Pb be the maximum tensile force reached before the material is broken, and Fo is the cross sectional area of the specimen, and the tensile strength is b= Pb/Fo (MPa).
4. elongation (Delta s)
When the material is broken, the percentage of plastic elongation and the length of the original sample is called elongation or elongation.
5. strength ratio (sigma s/ sigma B)
The ratio of the yield point (yield strength) to the tensile strength of steel is called the yield strength ratio. The greater the yield strength ratio, the higher the reliability of structural parts, the general carbon steel 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. hardness
Hardness indicates the ability of a material to resist hard material pressing into its surface. It is one of the important properties of metallic materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and hardness of Vivtorinox.
The Brinell hardness (HB)
At a certain load (usually 3000kg) to a certain size (diameter is 10mm) hardened steel ball is pressed into the surface of the material, for a period of time, to load, load ratio and area of indentation, the Brinell hardness value (HB), in kilograms force /mm2 (N/mm2).
The Rockwell hardness (HR)
When HB>450 or sample is too long, Brinell hardness test can not be used instead of Rockwell hardness measurement. It uses a diamond cone with a support angle of 120 degrees or a ball with a diameter of 1.59 and 3.18mm. The material is pressed into the surface of the material under certain loads. The hardness of the material is determined by the depth of the indentation. According to the hardness of the test material, three different scales are used to represent the hardness:
HRA: the hardness obtained by means of 60kg load and diamond cone press. Used for extremely hard materials (such as cemented carbide, etc.).
HRB: the hardness of the steel ball, which is hardened by 100kg load and diameter 1.58mm, is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: the hardness obtained by means of a 150kg load and a diamond cone press. Used of materials of high hardness (e.g. hardened steel, etc.).
The Vivtorinox hardness (HV)
A diamond square cone press with a load of less than 120kg and a support angle of 136 degrees is pressed into the material surface. The surface area of the indentation dent is divided by the load value, which is the Vivtorinox hardness (HV)
