The hardness of a metal is the ability of a metal material to resist local deformation, especially plastic deformation, indentation or scratches. It is an index to measure the hardness of a metal material. It can sensitively reflect the chemical composition, metallographic structure, The difference in heat treatment process and cold working deformation, testing the hardness of metal materials is very important in production, scientific research and engineering.
Hardness test can generally be divided into two types: press-in method and scoring method according to different force methods. In press-in method, it can be divided into static test method and dynamic test method according to the different afterburner speed. Among them, the static test method is the most widely used, and the common static test methods are Brinell hardness, Rockwell hardness and Vickers hardness.
Cemented carbide is a kind of alloy material made by the hard compound of refractory metal and bonding metal through powder metallurgy process, and it usually contains metal elements such as tungsten, cobalt, and titanium. Cemented carbide has a series of excellent properties such as high hardness, toughness, wear resistance, heat resistance, corrosion resistance, and high temperature resistance. It is known as "industrial teeth" and is mostly used to manufacture cutting tools, knives, wear-resistant parts, etc. , Widely used in military industry, aerospace, mechanical processing, metallurgy, petroleum drilling, mining tools, electronic communications, construction and other fields.
Hard alloy generally adopts Rockwell hardness (HRC) to test the hardness. Rockwell hardness is an index to determine the hardness value by the depth of indentation plastic deformation, with 0.002 mm as a hardness unit. In the Rockwell hardness test, using different indenters and different test forces will produce different combinations, corresponding to different scales of Rockwell hardness. The three most commonly used scales are A, B, and C, namely HRA, HRB, and HRC. According to the hardness of the experimental materials, the scales with different hardness ranges are used to indicate:
HRA is the hardness obtained with a 60Kg load and a diamond cone indenter, and is used for materials with higher hardness. For example: steel sheet, cemented carbide.
HRB is the hardness obtained by using a 100Kg load and a hardened steel ball with a diameter of 1.5875mm. It is used for materials with lower hardness. For example: mild steel, non-ferrous metals, annealed steel, etc.
HRC is the hardness obtained with a load of 150Kg and a diamond cone indenter, and is used for materials with higher hardness. For example: hardened steel, cast iron, etc.
To test the hardness of cemented carbide, generally use Rockwell hardness tester HRA scale to test. The Rockwell hardness tester is the world's first Rockwell hardness tester designed based on the Rockwell hardness test principle. It only needs to touch the sample on one side to test the hardness of the metal. The Rockwell hardness tester is adsorbed on the surface of the steel by magnetic force. , No need to support the sample, the test accuracy conforms to the standard GB/T230, ISO6508.
The advantage of Rockwell hardness testing is that materials with higher hardness can be measured by changing the test scale. The indentation is small, it is a non-destructive test, the test method is relatively simple, and it can be used for semi-finished or finished product inspection. The disadvantage is that the indentation is small and the representativeness is poor. Due to defects such as segregation and uneven structure in the material, the measured hardness value has poor repeatability and large dispersion. In addition, the hardness values measured with different scales have no inherent relationship with each other and cannot be directly compared.
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