Rockwell hardness (HRC), Brinell hardness (HB), Vickers hardness (HV) expression methods and hardness comparison difference and conversion

Rockwell hardness (HRC), Brinell hardness (HB), Vickers hardness (HV) expression methods and hardness comparison difference and conversion

metal materials to resist the indentation of hard objects on the surface is called hardness.

According to different test methods and application scope, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. Commonly used for pipes are Brinell, Rockwell, and Vickers hardness.

A. Brinell hardness (HB) Use steel balls or hard alloy balls with a certain diameter to press into the surface of the sample with the specified test force (F), remove the test force after the specified holding time, and measure the indentation diameter (L) on the surface of the sample. The Brinell hardness value is the quotient of the test force divided by indentation of the spherical surface area. It is expressed in HBS (steel ball) in N/mm2(MPa). The calculation formula is: where: f-test force pressed into the surface of the metal sample, n; D-diameter of steel ball for test, mm; D-average diameter of indentation, mm. The determination of Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2(MPa), and is not suitable for harder steel or thinner plates. In the steel pipe standard, Brinell hardness is the most widely used, and the hardness of the material is often expressed by the indentation diameter d, which is intuitive and convenient. For example: 120HBS10/1000130: indicates that the Brinell hardness value measured by a 10mm diameter steel ball is 120N/ mm2(MPa) under the action of 1000Kgf(9.807KN) test force for 30s (seconds).

B, Rockwell hardness (HK) Rockwell hardness test is the same as Brinell hardness test, are indentation test methods. The difference is that it measures the depth of the indentation. That is, under the sequential action of the initial test force (Fo) and the total test force (F), the pressure head (cone or steel ball in the steel plant) is pressed into the surface of the sample, after the specified holding time, the main test force is removed, and the hardness value is calculated with the measured residual indentation depth increment (e). Its value is an unnamed number, expressed by the symbol HR, and the scales used include 9 scales such as A, B, C, D, E, F, G, H, K, etc. Among them, the scales commonly used in steel hardness test are generally A, B and C, namely HRA, HRB and HRC. The hardness value is calculated by the following formula: when tested with a and c scales, HR = 100-e when tested with B scale, HR = 130-e formula e-residual indentation depth increment, which is expressed in the specified unit of 0.002mm, I .e. when the axial displacement of the indenter is one unit (0.002mm), it is equivalent to a number of Rockwell hardness changes. The higher the e value, the lower the hardness of the metal, and vice versa. The applicable scope of the above three scales is as follows: HRA (diamond cone indenter) 20-88HRC (diamond cone indenter) 20-70HRB (1.588mm diameter steel ball indenter) 20-100 Rockwell hardness test is currently widely used method, of which HRC is second only to Brinell hardness HB in steel pipe standard. Rockwell hardness can be applied to the determination of metal materials from extremely soft to extremely hard. It makes up for the Brinell method. It is simpler than the Brinell method and can be directly read from the dial of the hardness machine. However, due to its small indentation, the hardness value is not as accurate as the Brinell method.

C, Vickers hardness (HV) Vickers hardness test is also an indentation test method. A regular quadrangular pyramid diamond indenter with an angle of 1360 on the opposite surface is pressed into the test surface with a selected test force (F), the test force is removed after the specified holding time, and the length of the two diagonal lines of indentation is measured. Vickers hardness value is the quotient of test force divided by indentation surface area, and its calculation formula is: in the formula: HV -- Vickers hardness symbol, N/mm2(MPa);F-test force, n; D-arithmetic average of two diagonal lines of indentation, mm. The test force F used for Vickers hardness is 5(49.03), 10(98.07), 20(196.1), 30(294.2), 50(490.3), 100(980.7)Kgf(N) and other six levels, and the measurable hardness value range is 5 ~ 1000HV. An example of the expression method: 640HV30/20 indicates that the Vickers hardness value measured by holding the test force of 30Hgf(294.2N) for 20 seconds is 640N/mm2(MPa). The Vickers hardness method can be used to determine the hardness of very thin metal materials and surface layers. It has the main advantages of the Brinell and Rockwell methods, and overcomes their basic shortcomings, but it is not as simple as the Rockwell method. The Vickers method is rarely used in steel pipe standards. Hardness is a performance index to measure the softness and hardness of a material. There are many methods of hardness test, the principle is different, and the measured hardness value and meaning are not exactly the same. The most common is the static load indentation 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 values indicate the ability of the material surface to resist the indentation of hard objects. The most popular Richter hardness (HL) and Shore hardness (HS) belong to the rebound hardness test, and their values represent the magnitude of the elastic deformation work of metals.

Therefore, hardness is not a simple physical quantity, but a comprehensive performance index reflecting the elasticity, plasticity, strength and toughness of the material.

1. Hardness of steel: The code of metal hardness (Hardness) is H. According to the different hardness test methods, the conventional expression is Brinell (HB), Rockwell (HRC), Vickers (HV), Richter (HL) hardness, etc., among which HB and HRC are more commonly used. HB has a wide range of applications, HRC is suitable for surface high hardness materials, such as heat treatment hardness, etc. The difference between the two lies in the difference in the probe of the hardness tester. The probe of the Brinell hardness tester is a steel ball, while the probe of the Rockwell hardness tester is diamond. HV-suitable for microscopic analysis. Vickers hardness (HV) is pressed into the surface of the material with a load of less than 120kg and a diamond square cone indenter with an apex angle of 136, and the surface area of the indentation pit of the material is divided by the load value, which is the Vickers hardness value (HV). HL portable hardness tester is convenient to measure, and bounces after the impact ball head impacts the hardness surface. The hardness is calculated by using the ratio of the rebound speed of the punch at a distance of 1mm from the sample surface to the impact speed. The formula is: Richter hardness HL = 1000 × VB (rebound speed)/ VA (impact speed). At present, the most commonly used portable Leeb hardness tester can be converted into Brinell (HB), Rockwell (HRC), Vickers (HV) and Shore (HS) hardness after measurement with Leeb (HL). Or use the Richter principle to directly use Brinell (HB), Rockwell (HRC), Vickers (HV), Richter (HL), Shore (HS) to measure hardness values.

2. HB-Brinell Hardness: Brinell Hardness (HB) is generally used when materials are soft, such as non-ferrous metals, steel before heat treatment or after annealing. Rockwell hardness (HRC) is generally used for materials with higher hardness, such as hardness after heat treatment, etc. Cloth hardness (HB) is a test load of a certain size. A hardened steel ball or cemented carbide ball with a certain diameter is pressed into the surface of the tested metal for a specified time, and then the load is unloaded to measure the indentation diameter of the measured surface. The cloth hardness value is the quotient of the load divided by the indentation spherical surface area. Generally, hardened steel balls of a certain size (generally 10mm in diameter) are pressed into the surface of the material with a certain load (generally 3000kg) and kept for a period of time. After unloading, the ratio of the load to the indentation area is the Brinell hardness value (HB), and the unit is kg force/mm2 (N/mm2). (For details of cloth hardness (HB), please click "Brinell Hardness Machine (Meter) HB-3000B/TH600")

3. Lo-type hardness is determined by indentation plastic deformation depth. Take 0.002mm as a hardness unit. When HB>450 or the sample is too small, Brinell hardness test cannot be used instead of Rockwell hardness measurement. It uses a diamond cone with an apex angle of 120 or a steel ball with a diameter of 1.59mm and 3.18mm to press into the surface of the measured material under a certain load, and calculates the hardness of the material from the depth of the indentation. According to the hardness of the test materials, it is expressed in three different scales: HRA: is the hardness obtained by 60kg load and diamond cone indenter, and is used for materials with extremely high hardness (such as hard alloy, etc.). HRB: The hardness obtained by using 100kg load and 1.58mm diameter hardened steel balls is used for materials with lower hardness (such as annealed steel, cast iron, etc.). HRC: It is the hardness obtained by 150kg load and diamond cone indenter, and is used for materials with high hardness (such as hardened steel, etc.). In addition: 1.HRC means Lo-type hardness C scale 2.HRC and HB are widely used in production 3.HRC scope of application HRC 20-67, which is equivalent to HB225-650 Lo-type hardness A scale HRA if the hardness is higher than this range. If the hardness is lower than this range, use the Luo type hardness B scale HRB. The upper limit value of cloth hardness HB650 cannot be higher than this value.

4. The indenter of Rockwell hardness tester C scale is a diamond cone with an apex angle of 120 degrees. The test load is a definite value. The Chinese standard is 150kg force. The indenter of Brinell hardness tester is hardened steel ball (HBS) or hard alloy ball (HBW). The test load varies with the diameter of the ball, ranging from 3000 to 31.25kg force.

5. Luo type hardness indentation is very small, the measured value is local, and the average value must be measured at several points. it is suitable for finished products and flakes, and belongs to nondestructive testing. Cloth type hardness indentation is large, the measured value is accurate, not applicable to finished products and flakes, generally not classified as non-destructive testing.

6. The hardness value of Lo-type hardness is an unnamed number, no unit. (Therefore, it is customary to say that the hardness of the Luo type is incorrect.) The hardness value of cloth hardness has units and has a certain approximate relationship with tensile strength. 7. Luo-type hardness is directly displayed on the dial or can be displayed digitally. It is convenient to operate, fast and intuitive, and is suitable for mass production. Cloth hardness needs to measure the indentation diameter with a microscope, and then look up the table or calculate, which is more complicated. 8. Under certain conditions, HB and HRC can look up tables interchangeably. The mental calculation formula can be roughly recorded as: 1HRC ≈ 1/10HB.