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Needless to say, the tons of steel strips sold in the market need to be exposed to the hardness of different materials. Sometimes the hardness is expressed in different ways, and we need to convert each other. But there are nine out of ten people who can't handle these things for a while.
Brinell hardness (HB)
Press a hardened steel ball of a certain size (generally 10mm in diameter) into the surface of the material with a certain load (generally 3000kg) and keep it for a period of time. After the load is removed, the ratio of the load to its indentation area is the Brinell hardness value ( HB) in kilogram force/mm2 (N/mm2).
Rockwell hardness (HR
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement is used instead. It uses a diamond cone with an apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18mm to press into the surface of the tested material under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the different hardness of the test material, it is expressed in three different scales:
• HRA: is the hardness obtained by using a 60kg load and a diamond cone indenter. It is used for materials with extremely high hardness (such as cemented carbide, etc.).
• HRB: Hardened steel balls with a load of 100kg and a diameter of 1.58mm are used to obtain the hardness, and are used for materials with lower hardness (such as annealed steel, cast iron, etc.).
• HRC: It is the hardness obtained by using a load of 150kg and a diamond cone indenter. It is used for materials with high hardness (such as hardened steel, etc.).
Vickers hardness (HV)
Use a load within 120kg and a diamond square cone indenter with an apex angle of 136° to press into the surface of the material, and divide the surface area of the material indentation pit by the load value, which is the Vickers hardness HV value (kgf/mm2).
Note: A, B, C in HRA, HRB, HRC, etc. in Rockwell hardness are three different standards, called scale A, scale B, scale C. The Rockwell hardness test is one of several common indentation hardness tests used today. The initial pressure of the three scales is 98.07N (10kgf), and the hardness value is calculated according to the indentation depth. Scale A uses a ball-cone diamond indenter, then pressurized to 588.4N (60kgf); Scale B uses a steel ball with a diameter of 1.588mm (1/16 inch) as the indenter, and then pressurized to 980.7N (total 100kgf); while the scale C uses the same spherical cone rhombus as the scale A as the indenter, but the force after pressing is 1471N (total 150kgf). Therefore, scale B is suitable for relatively soft materials, while scale C is suitable for harder materials. Practice has proved that among various hardness values of metal materials, there is an approximate corresponding relationship between the hardness value and the strength value. 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 higher the plastic deformation resistance, and the higher the hardness value. However, the conversion relationship of various materials is not consistent.
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