# The difference between HRA, HRB and HRC in Rockwell hardness

The so-called various hardnesses are the values ​​measured by different measurement methods according to the hardness level. They are organized according to some standards for reference. Please read the standards for details.
⑴Brinell hardness (HB) Press a hardened steel ball of a certain size (typically 10mm in diameter) into the surface of the material with a certain load (typically 3000kg), and keep it for a period of time. After the load is removed, the ratio of the load to the indentation area, It is the Brinell hardness value (HB), and the unit is kilogram force/mm2 (N/mm2). To
⑵Rockwell 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:
There are three methods for measuring Rockwell hardness:
1) HRA, using an indenter with diamonds, the measured value of the load is 60 kg;
2) HRC, the measured value with a load of 150 kg;
3) HRB, with a 1/16-inch steel ball indenter, the measured value of the load is 100 kg.
⑶ Vickers hardness (HV) with a load of less than 120kg and a diamond square cone indenter with an apex angle of 136° into the surface of the material, the surface area of ​​the material indentation pit is divided by the load value to obtain the Vickers hardness value ( HV)
The difference between HRA, HRB and HRC in Rockwell hardness
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 with the 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) = BHN/10-3 　 hardness measurement range: HS<100HB<500HRC<70HV<1300(80~88)HRA, (85~95) HRB, (20~70 )HRC In Rockwell hardness, A, B, C in HRA, HRB, HRC, etc. are three different standards, called scale A, scale B, and scale C. 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 according to 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. 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. To
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), keep it for a period of time, after removing the load, the ratio of the load to the indentation area , Is the Brinell hardness value (HB), the unit is kilogram force/mm2 (N/mm2). To
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 is expressed in three different scales: HRA: It is the hardness obtained with a 60kg load and a diamond cone indenter, and is 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 load of 150kg and a diamond cone indenter. It is used for materials with high hardness (such as hardened steel, etc.).
3. Vickers hardness (HV) A diamond square cone indenter with a load of less than 120kg and an apex angle of 136° 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 HV Value (kgf/mm2). “HK=139.54•P/L2. Where: HK-Knoop hardness, Mpa; P-load, kg; L-diagonal length of pit, mm. China and European countries use Vickers hardness, while the United States uses Knoop hardness. Megapascals (MPa) is the legal measurement unit of microhardness, while kg/mm2 is the commonly used unit for calculating hardness before. The conversion formula between them is 1kg/mm2=9.80665Mpa. The specific difference between Rockwell hardness (HRC) and Brinell hardness (HB) and the converted hardness is a performance index to measure the hardness of the material. There are many methods of hardness test, the principles are different, and the hardness values ​​and meanings measured are not exactly the same. The most commonly used is the static load intrusion method hardness test, that is, Brinell hardness HB, Rockwell hardness HRA, HRB, HRC, Vickers hardness HV, rubber and plastic Shore hardness HA, HD and other hardness. The value indicates that the surface of the material resists hard objects. The ability to press in. The Leeb hardness Hl and Shore hardness HS belong to the rebound method hardness test, and their value represents the magnitude of the metal’s elastic deformation work. Therefore, the hardness is not a pure physical quantity, but a comprehensive performance index reflecting the elasticity, plasticity, strength and toughness of the material.
1. HRC means Rockwell hardness C scale,
2. HRC and HB are widely used in production
3. The applicable range of HRC is HRC 20-67, which is equivalent to HB225-650. If the hardness is higher than this range, use Rockwell hardness A scale HRA. If the hardness is lower than this range, use Rockwell hardness B scale HRB. The upper limit of Brinell hardness HB650 cannot be higher than this value. To
4. The indenter of the Rockwell hardness tester C scale is a diamond cone with an apex angle of 120 degrees, and the test load is a certain value. The Chinese standard is 150 kgf. The indenter of the Brinell hardness tester is a hardened steel ball HBS or a cemented carbide ball HBW. The test load varies with the diameter of the ball, ranging from 3000 to 31.25 kgf. To
5. Rockwell hardness indentation is very small, and the measured value is local. It is necessary to measure several points to find the average value. It is suitable for finished products and thin slices, and is classified as non-destructive testing. The cloth-type hardness indentation is large and the measured value is accurate. It is not suitable for finished products and sheets, and is generally not classified as non-destructive testing. To
6. The hardness value of Rockwell hardness is an unknown number and has no unit. Therefore, it is not correct to say how much Rockwell hardness is. The hardness value of Brinell hardness has a unit and has a certain approximate relationship with tensile strength. To
7. The Rockwell hardness can be displayed directly on the dial or digitally. It is easy to operate, fast and intuitive, and is suitable for mass production. Brinell hardness needs to use a microscope to measure the indentation diameter, and then look up the table or calculate, the operation is more cumbersome. To
8. Under certain conditions, HB and HRC can be interchanged with look-up tables. 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.