Hardness is a measure of the softness of the material. There are many different hardness test methods whose principle are definitely different, measured hardness values and meaning are not exactly the same. Brinell hardness(HB), Rockwell hardness(HRA, HRB, HRC), Vickers hardness (HV), rubber and plastic Shore hardness (HA, HD), etc. are the most common static load press hardness tests of which the value of the material show its surface ability to resistant the press of hard objects. Therefore, the hardness is not a simple physical quantity, it reflects a comprehensive performance including elasticity, plasticity, strength and toughness of the material.
Hardness of steel: the code of steel Hardness is H. Depending on the different hardness test method,
● The common methods are Brinell hardness (HB), Rockwell hardness (HRC), Vickers hardness (HV), and Richard hardness (HL), among which HB and HRC are more commonly used.
● HB has wide range of applications, while HRC is suit for high hardness materials, such as heat treatment hardness. The difference between the two is that they have different probe. The probe of Brinell hardness is the carbide ball, and the probe of Rockwell hardness is diamond.
● HV is suitable for microscopic analysis. Vickers hardness (HV) press into the material surface with diamond square cone for about 120kg load and the top angle of 136 °, then the surface area of the indentation of the material is divided by the load value that is, Vickers hardness (HV ).
● HL hand-held hardness tester is easy to measure. The impact ball assaults the hardness surface to generate bounce; the hardness is calculate by the ratio of the impact speed and rebound speed at 1mm between the impact ball and the sample. The formula: Hardness HL = 1000 × VB (rebound speed) / VA (impact speed).
HB - Brinell Hardness:
Brinell hardness (HB) is generally used for the soft material, such as non-ferrous metals, steel before heat treated or after annealing. Rockwell hardness (HRC) is generally used for high hardness materials, such as the hardness after heat treatment and so on.
Brinell hardness (HB) press a certain diameter of hardened steel ball or carbide ball into the metal surface to be measured with a certain size of the test force to maintain the specified time, and then remove the test force, measuring the measured surface indentation diameter. The Brinell hardness value is the quotient of the indentation spherical surface area divided by the test force. Generally: press a certain size (diameter is generally 10mm) of hardened steel ball into the material surface with a certain test force (usually 3000kg) to maintain a period of time, then remove the test force, the ratio of load and its indentation area is the Brinell hardness (HB) in kg / mm2 (N / mm2). (For details of Brinell hardness (HB), please click "Brinell hardness tester PHB-3000")
Rockwell hardness (HR) depend on the indentation plastic deformation depth to determine the hardness value of the index with 0.002 mm as a unit of hardness. When HB> 450 or the sample is too small, Rockwell hardness tester is suitable to use rather than Brinell hardness tester. It press a vertex angle of 120 ° diamond cone or diameter of 1.588, 3.175mm carbide ball into the surface of the measured material with a certain test force. And according to the depth of the indentation to calculate the hardness of the material. According to the hardness of the test material, there are three different scales:
HRA: It is suitable for high hardness materials (such as cemented carbide, etc.). The hardness is obtained according to the 60kgf test force and diamond indenter,
HRB: It is suitable for low hardness materials (such as annealing steel, cast iron, etc.). The hardness is obtained by 100kgf test force and diameter 1.588mm carbide ball.
HRC: It is suitable for high hardness materials (such as hardened steel, etc.). According to the 150kgf test force and diamond indenter to calculate hardness.
(1) HRC is the Rockwell hardness C scale.
(2) HRC and HB is widely used in the production industry.
(3) HRC is suitable for HRC 20-88, equivalent to HB225-650
Rockwell hardness A scale is useful if the hardness is higher than this range. If the hardness is below this range, you can use the Rockwell Hardness B scale HRB. The hardness value of Brinell hardness tester can not be higher than HB650.
(4) The indenter of Rockwell hardness tester C gauge is diamond indenter with the vertex angle of 120 degrees, the test force is a certain value, and the Chinese standard is 150 kg force.
The indenter of Brinell hardness tester is the hardened steel ball (HBS) or carbide ball (HBW), the test force varies with the diameter of ball from 3000 to 31.25 kg force.
(5) Rockwell hardness indentation is small. As the measured value has locality, more points need to be measured to find the average. It is attributed to a class of non-destructive testing for finished products and flakes.
Brinell hardness indentation is large with standard measured value. Generally, it do not belong to the class of non-destructive testing and not suitable for finished products and flakes.
(6) The hardness value of Rockwell hardness tester is an unknown number without unit. (So it is customary to say that the degree of hardness is not correct.)
The hardness value of Brinell hardness tester has an unit, and it has a certain approximate relationship with the tensile strength.
(7) Rockwell hardness display directly on the dial or it can also be digital display. It is suitable for mass production with the advantages of simple operation, fast and intuitive.
Brinell hardness tester need to use a microscope to measure the indentation diameter, and then look up the table or calculation. Its operation is more cumbersome.
(8) Under certain conditions, HB and HRC can look-up table and swap. The conversion formula can be roughly recorded as: 1HRC ≈ 1 / 10HB.