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How to detect the hardness of cemented carbide?

April 15, 2020

The hardness of the metal is the ability of the metal material to resist local deformation, especially plastic deformation, indentation or scratching. It is an indicator to measure the degree of softness and hardness of the metal material. It can sensitively reflect the metal material's chemical composition, metallographic structure, Differences in heat treatment process and cold working deformation, etc., testing the hardness of metal materials is essential in production, scientific research and engineering.


Hardness test can be divided into two types: press-in method and scoring method according to different stress methods. In the press-in method, it can be divided into static test method and dynamic test method according to different forcing speed. Among them, the static test method is the most commonly used, and the common static test methods are Brinell hardness, Rockwell hardness and Vickers hardness.


Cemented carbide is an alloy material made of hard compound of refractory metal and bonding metal through powder metallurgy process, and it usually contains metal elements such as tungsten, cobalt and titanium. 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, oil drilling, mining tools, electronic communications, construction and other fields.


Cemented carbide generally uses Rockwell hardness (HRC) to detect hardness. Rockwell hardness is an index used to determine the hardness value of the depth of plastic deformation of indentation, with 0.002 mm as a hardness unit. In Rockwell hardness test, using different indenters and different test forces will produce different combinations, corresponding to different Rockwell hardness scales. The three most commonly used scales are A, B, and C, that is, HRA, HRB, and HRC. According to the hardness of the experimental materials, different scales with different hardness ranges are used to represent:


HRA is the hardness obtained by using 60Kg load and diamond cone indenter, which is used for materials with higher hardness. For example: steel sheet, cemented carbide.


HRB is the hardness obtained by using 100Kg load and 1.5875mm diameter hardened steel ball, which is used for materials with lower hardness. For example: mild steel, non-ferrous metals, annealed steel, etc.


HRC is the hardness obtained by 150Kg load and diamond cone indenter, which is used for materials with higher hardness. For example: hardened steel, cast iron, etc.


Test the hardness of cemented carbide generally using Rockwell hardness tester HRA scale to detect. Rockwell hardness tester is the world's first Rockwell hardness tester designed based on the Rockwell hardness test principle. It only needs one side to contact the sample to test the metal hardness. The Rockwell hardness tester is attached to the steel surface by magnetic force. , No need to support the sample, the test accuracy meets the standards GB / T230, ISO6508.


The advantage of Rockwell hardness testing is that it can measure materials with higher hardness by changing the test scale. The indentation is small, which is a non-destructive test. The test method is relatively simple and 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 are not intrinsically related to each other, nor can they be directly compared.