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How to detect metal hardness

Writer:Anonymous   2020-02-26 11:54:03

Hardness is the ability of a solid material to resist elastic deformation, plastic deformation, or damage. It is an indicator for measuring the hardness of a material. The higher the resistance, the higher the hardness value. Hardness is related to the chemical composition, microstructure, processing, working environment and mechanical properties of the material. Chengcheng Xiaobian introduces three common methods of metal hardness testing.

The hardness value is the same as the hardness test method, and its physical meaning is also the same. The hardness test can be divided into static pressure method (such as Brinell hardness, Rockwell hardness, Vickers hardness, etc.), scratch method (such as Mohs hardness), and rebound method (such as Shore hardness) according to the test method. And microhardness, iy temperature hardness and other methods. In general, the most common method for testing the hardness of steel is the file test method. That is, file the file on the edge of the workpiece. Too scientific. The hardness tester is more accurate to test the hardness value, which is a commonly used method for modern test hardness. At present, commonly used hardness measurement methods include Brinell hardness, Rockwell hardness, and Vickers hardness.

Brinell hardness (HB)

The Brinell hardness value is the quotient obtained by dividing the load by the indentation (spherical surface product) as HB [N (kgf / mm2). It is a test load of a certain size, a hardened steel ball of a certain diameter or a hardened Carbide alloy ball is pressed into the metal gauge to be measured, held for a predetermined time, then unloaded, and the diameter of the indentation is measured. Generally, the hardened steel ball with a diameter of 10 mm is pressed into the material gauge with a load of 3000 kg Hold for a period of time. After deloading, the ratio of the product of the load and its indentation is the Brinell hardness value (HB) in kgf / mm2 (N / mm2). The Brinell hardness (HB) and tensile strength have a certain value. The approximate relationship is generally used for the hardness testing of softer materials. The Brinell hardness method is commonly used in production to determine the hardness of roughened or semi-finished steel parts such as annealed, normalized and quenched and tempered, and cast iron, non-ferrous metals, and alloy structural steel. But because the Brinell hardness indentation is large, it is a destructive test, so it is suitable for measuring finished products and sheets. The Brinell hardness requires measuring the indentation diameter with a microscope, and then checking the table or calculation, which is more complicated. The maximum limit of Brinell hardness detection The value is HB650, generally when HB> 450 or the sample is too small, small energy And switch to a Rockwell hardness measurement Brinell hardness test.

Rockwell Hardness (HRC)

Rockwell hardness is determined by the plastic deformation depth of the indentation. It is a diamond cone with a vertex angle of 120 "or a hardened steel ball with a diameter of 1.58mm and 3.18mm. It is pressed into the table of material under a certain load, and 0.002 mm is used as a hardness unit. Determining the hardness of the material in depth. The Rockwell hardness value is an unknown number and no unit. According to the test scale, the scale is divided into two kinds of scales: HRA, HRB, HRC.

HRA: It is a hardness obtained by pressing with a diamond cone indenter with a load of 60kg. It is used for materials with extremely high hardness (such as cemented carbide).

HRB: It is a hardened steel ball with a load of 100kg and a diameter of 1.58mm. The hardness is determined and used for materials with lower hardness (such as annealed steel, cast iron, etc.)

HRC: It is a hardness obtained by pressing with a diamond cone indenter with a load of 150kg. It is used for materials with a very high hardness (such as quenched steel).

According to the hardness of the test material, the measurement range and application range of the two types of hardness scales are also the same. The applicable range of HRC is HRC20-67 (equivalent to HB225-650). If the hardness iu is within this range, use HRA to test. If the hardness is lower than this range, use Rockwell hardness HRB. In general production, HR (is most widely used.

The Rockwell hardness indentation is small, and Siyi measures the hardness of thinner and harder materials and finished products. Siyi displays directly on the dial or can display digitally. It is easy to operate, fast and intuitive, and is suitable for mass production. The Rockwell hardness measurement value is local, and the average value must be measured after a few points. It is classified as a non-destructive test and is suitable for finished products and sheets.

Vickers hardness (HV)

Vickers hardness (H is a table of materials that are pressed into a diamond square cone indenter with a load of less than 120kg and a vertex angle of 136 ", and the material indentation (f" product of 1 pit table) is divided by the load value It is the Vickers hardness value (HV). HV is suitable for microscopic analysis and suitable for measuring very thin samples. Under certain conditions, HB and HRC can refer to Table 4. The empirical formula is HRC = 1 / 10HB. There is an approximately corresponding relationship between various hardness values of metal materials, and between hardness values and strength values. 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 more plastic deformation resistance Therefore, the hardness test is the simplest and easiest test method in the mechanical performance test. In order to replace some mechanical performance tests with the hardness test, a more accurate conversion relationship between hardness and strength is required in production).