1. Introduction to hardness:
Hardness refers to the ability of a material to resist the pressing of hard objects into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are 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 with a certain load (usually 3000kg) and keep it for a period of time. After the load is removed, the ratio of the load to the indentation area is the Brinell hardness value ( HB), the unit is kilogram force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement can be used instead. It uses a diamond cone with an apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18mm, which is pressed into the surface of the material to be tested under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the hardness of the test material, it can be expressed in three different scales:
• HRA: It is the hardness obtained with a 60kg load and a diamond cone indenter, used for extremely hard materials (such as cemented carbide, etc.).
• HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm, which is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
• HRC: It is the hardness obtained with a 150kg load and a diamond cone indenter, and is used for materials with high hardness (such as hardened steel, etc.).
3. Vickers hardness (HV)
With a load of less than 120kg and a diamond square cone indenter with an apex angle of 136°, it is pressed into the surface of the material, and the surface area of the material indentation pit is divided by the load value to obtain the Vickers hardness HV value (kgf/mm2).
Note: In Rockwell hardness, A, B, C in HRA, HRB, HRC, etc. are three different standards, called scale A, scale B, and scale C. The Rockwell hardness test is one of several common indentation hardness tests used today. The initial pressure of the three scales is 98.07N (10kgf), and finally the hardness value is calculated based on the indentation depth. Ruler A uses a spherical cone diamond indenter, and then pressurizes to 588.4N (60kgf); Ruler B uses a steel ball with a diameter of 1.588mm (1/16 inch) as the indenter, and then pressurizes to 980.7N (Total 100kgf); while scale C uses the same spherical cone diamond as scale A as the indenter, but the pressure after pressure is 1471N (total 150kgf). Therefore, ruler B is suitable for relatively soft materials, while ruler C is suitable for harder materials. Practice has proved that between various hardness values of metal materials, there is an approximate corresponding relationship between the hardness value and the strength value. Because the hardness value is determined by the initial plastic deformation resistance and the continued plastic deformation resistance, the higher the strength of the material, the higher the plastic deformation resistance and the higher the hardness value. However, the conversion relationship of various materials is not consistent.
2. Hardness comparison table:
According to the German standard DIN50150, the following is a comparison table of the commonly used range of steel tensile strength and Vickers hardness, Brinell hardness, and Rockwell hardness.
Hardness test is the simplest and most feasible test method in mechanical performance test. In order to replace certain mechanical performance tests with hardness tests, a more accurate conversion relationship between hardness and strength is required in production. Practice has proved that between various hardness values of metal materials, there is an approximate corresponding relationship between the hardness value and the strength value. Because the hardness value is determined by the initial plastic deformation resistance and the continued plastic deformation resistance, the higher the strength of the material, the higher the plastic deformation resistance and the higher the hardness value.
3. Hardness conversion formula
1. Shore hardness (HS) = Boehre hardness (BHN)/10+12
2. Shore hardness (HS) = Rockwell hardness (HRC) + 15
3. Boehre hardness (BHN) = Rocker hardness (HV)
4. Rockwell hardness (HRC) = Borer hardness (BHN)/10-3
Hardness measurement range:
HS<100
HB<500
HRC<70
HV<1300
a) The value indicated in bold in this table is consistent with the hardness conversion value in ASTM-E140 Table 1, which is determined by the corresponding SAE-ASM-ASTM
Listed by the Federation.
b) The values in parentheses are out of range and are only for reference.
Use the Brinell hardness indentation diameter to directly convert the Rockwell hardness of the workpiece
At the production site, due to the limitation of testing instruments, the Brinell hardness tester is often used to measure the hardness of large quenched parts. If you want to know the Rockwell hardness value of the workpiece, the usual method is to first measure the Brinell hardness value, and then find the corresponding Rockwell hardness value according to the conversion table. This method is obviously a bit cumbersome. So, can the Rockwell hardness value of the workpiece be directly calculated based on the indentation diameter of the Brinell hardness tester? The answer is of course yes. According to the conversion table of Brinell hardness and Rockwell hardness, an empirical formula that is simple to calculate and easy to remember can be summed up: HRC = (479-100D)/4, where D is the Φ10mm steel ball indenter pressed against the workpiece under a pressure of 30KN The measured value of the diameter of the indentation. The error between the calculated value of this formula and the converted value is within the range of 0.5 to -1. This formula is very convenient to use in the field, so you may wish to give it a try.
