How to convert Brinell hardness to Rockwell hardness

The specific differences and conversion between Rockwell hardness (HRC) and Brinell hardness (HB): Hardness is a property indicator used to measure the degree of softness or hardness of a material. There are many methods for hardness testing, each with a different principle; the hardness values obtained and their meanings also vary. The most commonly used are hardness tests based on static load indentation, namely Brinell hardness (HB), Rockwell hardness (HRA, HRB, HRC), and Vickers hardness (HV); these values indicate the ability of a material’s surface to resist being pressed by hard objects. On the other hand, Rockwell hardness (HL) and Shore hardness (HS) belong to the rebound hardness testing methods, and their values represent the amount of elastic deformation work of the metal. Therefore, hardness is not a simple physical quantity; rather, it is a comprehensive performance indicator that reflects the elasticity, plasticity, strength, and toughness of a material. 1. Hardness of steel: The code for metal hardness is H. Depending on the hardness testing method, ●\"Conventional\" refers to hardnesses such as Brinell (HB), Rockwell (HRC), Vickers (HV), and Leeb (HL); among these, HB and HRC are the most commonly used. ●HB has a wide range of applications, while HRC is suitable for materials with high surface hardness, such as those with heat-treated hardness. The difference between the two lies in the probe used by the hardness tester: the probe of a Brinell hardness tester is a steel ball, while that of a Rockwell hardness tester is a diamond. ●HV – Suitable for microscopic analysis. Vickers hardness (HV) is determined by using a diamond square pyramid indenter with a load of 120 kg or less and an apex angle of 136° to press into the surface of the material; the Vickers hardness value is then calculated by dividing the surface area of the indentation formed in the material by the load applied. ●The HL handheld hardness tester is convenient to use; it generates a rebound effect after the impact head strikes the surface being tested for hardness ； Hardness is calculated using the ratio of the rebound velocity to the impact velocity at a distance of 1 mm from the sample surface; the formula is: Rockwell hardness HL = 1000 × VB (rebound velocity) / VA (impact velocity). The hardness values obtained using a portable Rockwell hardness tester in Rockwell (HL) scale can be converted to Brinell (HB), Rockwell (HRC), Vickers (HV), and Shore (HS) hardnesses. Alternatively, the Rockwell principle can be used to directly measure hardness values using Brinell (HB), Rockwell (HRC), Vickers (HV), Rockwell (HL), and Shore (HS) scales. 2. HB-Bruce hardness ； Brinell hardness (HB) is generally used for softer materials, such as non-ferrous metals, and steel before heat treatment or after annealing. Rockwell hardness (HRC) is generally used for materials with high hardness, such as those that have undergone heat treatment. Brinell hardness (HB) is determined by applying a test load of a certain magnitude to force a hardened steel ball or cemented carbide ball of a specific diameter into the surface of the metal being tested; after holding this pressure for a specified time, the load is removed and the diameter of the indentation left on the surface is measured. The Brinell hardness value is the quotient of the load divided by the surface area of the indented sphere. Generally, a hardened steel ball of a certain size (with a diameter of usually 10 mm) is pressed into the surface of the material under a specific load (typically 3000 kg). This pressure is maintained for a certain period of time; after the load is removed, the ratio of the load to the area of the indentation gives the Brinell hardness value (HB), which is expressed in kilogram-force per mm2 (N/mm2). 3. Rockwell hardness is a hardness value determined by the depth of plastic deformation of the indentation. 0.002 millimeters is used as a unit of hardness. When HB>450 or the sample is too small, the Brinell hardness test cannot be used; instead, the Rockwell hardness measurement should be employed. It involves using a diamond cone with an apex angle of 120° or steel balls with diameters of 1.59 and 3.18 mm to press against the surface of the material under test; the hardness of the material is determined from the depth of the indentation. Depending on the hardness of the test material, it is expressed using three different scales: HRA: This is the hardness determined using a 60 kg load and a diamond cone indenter, and it is used for materials with extremely high hardness (such as cemented carbides). HRB: It is the hardness obtained using a load of 100 kg and hardened steel balls with a diameter of 1.58 mm; it is used for materials with lower hardness (such as annealed steel, cast iron, etc.). HRC: It is the hardness determined using a 150 kg load and a diamond cone indenter, and it is used for materials with very high hardness (such as quenched steel). Additionally: 1. HRC refers to the Rockwell hardness scale C. 2. Both HRC and HB are widely used in production. 3. The applicable range for HRC is from 20 to 67, which corresponds to HB values of 225 to 650; if the hardness is above this range, the Rockwell hardness scale A, HRA, is used. If the hardness is below this range, the Rockwell hardness B scale HRB is used. The upper limit for Fabric type hardness is HB650; it must not exceed this value. 4. The indenter for the C scale of the Rockwell hardness tester is a diamond cone with an apex angle of 120 degrees; the testing load is a fixed value, which is 150 kilogram-force according to Chinese standards. The indenter of a Brinell hardness tester is a hardened steel ball (HBS) or a cemented carbide ball (HBW), and the testing load varies depending on the ball diameter, ranging from 3000 to 31.25 kilogram-force. 5. The Rockwell hardness indentation is very small, and the measurement values are localized; it is necessary to measure several points and take their average. It is suitable for finished products and thin sheets, and falls under the category of non-destructive testing. Brinell hardness produces larger indentations and yields accurate measurement values; it is not suitable for finished products and thin sheets, and is generally not classified as a type of non-destructive testing. 6. The hardness value of Rockwell hardness is an irrational number without any units. (Therefore, it is incorrect to refer to the Rockwell hardness as a certain degree.) ) The hardness value of fabric hardness is expressed in units, and it has a certain approximate relationship with tensile strength. 7. Rockwell hardness is displayed directly on the dial or in numerical form, offering convenient and quick operation; it is suitable for mass production. Brinell hardness requires measuring the indentation diameter under a microscope and then consulting a table or performing calculations, which is a rather cumbersome process. 8. Under certain conditions, HB and HRC can be interchanged using tables. Its mental calculation formula can be roughly remembered as: 1HRC≈1/10HB. The hardness test is the simplest and most straightforward method among mechanical property tests. In order to use hardness testing as a substitute for certain mechanical property tests, it is necessary in production to have a relatively accurate conversion relationship between hardness and strength. Practice has shown that there is an approximate corresponding relationship among various hardness values of metal materials, as well as between hardness values and strength values. Since the hardness value is determined by the resistance to initial plastic deformation and the resistance to further plastic deformation, the higher the strength of a material, the greater its resistance to plastic deformation, and thus the higher its hardness value.

Leeb hardness is a completely new method for measuring hardness that was first proposed in 1978 by Dr. LEEB from Switzerland. It is defined as a value calculated by using an impact body of specified mass to strike the surface of the specimen at a certain speed under elastic force; this value is obtained by taking the ratio of the rebound speed of the punch at a distance of 1 mm from the specimen’s surface to the impact speed. It is named Leeb hardness after Dr. LEEB who introduced this method. The calculation formula for the Rockwell hardness tester is as follows: HL=1000×Vb /Va, where HL represents the Rockwell hardness value; Va represents the impact velocity of the ball head, in m/s ； Vb————Rebound speed of the ball head, m/s.

HB and HRC can be converted using a table. Its mental calculation formula can be roughly remembered as: 1HRC≈1/10HB.

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