Contents
1. yield point(0σs)
When the steel or sample is stretched, when the stress exceeds the elastic limit, even if the stress does not increase, the steel or specimen still continues to undergo obvious plastic deformation, which is called yield. The minimum stress value of the yield phenomenon is the yield point.
Let Ps be the external force at the yield point s, and Fo is the sample break area, then the yield point σ s = Ps / Fo (MPa)
MPa is called the Mpa equal to N (Newton) / mm2
(MPa=106Pa, Pa: Pasca = N/m2)
2. Yield Strength (0σ 0.2)
The yield point of some metal materials is not obvious and is difficult to measure. Therefore, to measure the yield characteristics of the material, the stress when the permanent residual plastic deformation is equal to a certain value (generally 0.2% of the original length) is stipulated, which is called conditional yield strength or yield strength σ 0.2.
3. Tensile strength (0σ b)
The maximum stress value achieved from the material’s beginning to the fracture time during stretching indicates the size of the steel’s ability to resist breaking. It corresponds to the tensile strength, compressive strength, bending strength, etc.
Let Pb be the maximum tensile force before the material is pulled and Fo is the section area of the sample, so the tensile strength σ b = Pb / Fo (MPa).
4. Elongation rate (0δs)
After the material is pulled, the percentage of its plastic elongation length to the length of the original sample is called elongation or elongation rate.
5. Fion ratio (0σs/0σb)
The ratio of yield point (yield strength) to tensile strength of steel is called the yield strength ratio. The greater the bending strength ratio, the higher the reliability of the structural parts. Carbon steel’s general yield strength ratio is 0.6-0.65, and the low alloy structural steel is 0.65-0.75 alloy structural steel is 0.84-0.86.
6. Hardness
Hardness indicates the material’s ability to resist the pressing of a hard object onto its surface. It is one of the important performance indexes of metal materials. Generally, the higher the hardness, the better the wear resistance. The hardness indexes used are Brinell, Rockwell, and Vickers.
⑴ Brinell hardness (HB)
With a specific load (generally 3000kg), the hardened steel ball of a specific size (typically 10mm in diameter) is pressed into the material’s surface for some time. After deloading, the ratio of the load to the indentation area is the Brinell hardness value (HB) in kg force / mm2 (N/mm2).
⑵ Rockwell hardness (HR)
When HB> 450 or the sample is small, the Brinell hardness test cannot be used instead of the Rockwell hardness measurement. It is a diamond cone with a top angle of 120° or a steel ball with a diameter of 1.59,3.18mm, pressed into the surface of the measured material under a certain load. Then the hardness of the material is determined by the depth of the indentation. According to the different hardness of the test material, there are three different scales to represent the following values:
HRA is the hardness obtained from a 60kg load and diamond cone press, and it is used for extremely high-hardness materials (such as carbide, etc.).
HRB: it is a steel ball with a 100kg load and 1.58mm diameter, and the hardness is used for materials with low hardness (such as annealed steel, cast iron, etc.).
HRC is the hardness obtained using a 150kg load and diamond cone press for high-hardness materials (such as quenching steel).
⑶ Vickers Hardness (HV)
The diamond square cone press with a load within 120kg and a top angle of 136° is pressed into the material surface, and the surface area of the material indentation pit divided by the load value is the Vicker hardness value (HV)
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