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When purchasing stainless steel strips, we need to contact the hardness of different stainless steel materials. Sometimes the hardness is expressed in different ways and we need to convert them. But most people can’t handle these things at once. Brinell hardness (HB) A hardened steel ball of a certain size (usually 10mm in diameter) is pressed into the surface of the material with a certain load (usually 3000kg) and kept for a period of time. After the load is removed, the ratio of the load to the 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 Rockwell hardness measurement is used instead. It uses a diamond cone with a vertex angle of 120° or a steel ball with a diameter of 1.59 or 3.18 mm to press into the surface of the material under test under a certain load, and the hardness of the material is calculated from the depth of the indentation. According to the hardness of the test material, it is expressed in three different scales: HRA: It is the hardness obtained by using a 60kg load and a diamond cone indenter, which is used for materials with extremely high hardness (such as cemented carbide, etc.). HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm, which is used for materials with lower hardness (such as annealed steel, cast iron, etc.). HRC: It is the hardness obtained by using a 150kg load and a diamond cone indenter, which is used for materials with very high hardness (such as hardened steel, etc.). Vickers hardness (HV) Use a diamond square cone indenter with a load of less than 120kg and a vertex angle of 136° to press into the material surface, and divide the surface area of ​​the indentation by the load value to obtain the Vickers hardness HV value (kgf/mm2). Note: A, B, and C in HRA, HRB, and HRC in Rockwell hardness are three different standards, called scale A, scale B, and scale C. Rockwell hardness test is one of the common indentation hardness tests used today. The initial pressure of the three scales is 98.07N (10kgf), and the hardness value is calculated based on the indentation depth. Scale A uses a spherical cone diamond indenter, and then pressurizes to 588.4N (60kgf); Scale B uses a steel ball with a diameter of 1.588mm (1/16 inch) as an indenter, and then pressurizes to 980.7N (100kgf); and Scale C uses the same spherical cone diamond as the indenter as Scale A, but the force after pressurization is 1471N (150kgf). Therefore, Scale B is suitable for relatively soft materials, while Scale C is suitable for harder materials. Practice has proved that there is an approximate corresponding relationship between the various hardness values ​​of metal materials and 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 material strength, the higher the plastic deformation resistance, and the higher the hardness value. However, the conversion relationship of various materials is not consistent.