Hardness testing is one of the simplest and most readily available methods in mechanical property testing. To replace certain mechanical property tests with hardness testing, a relatively accurate conversion relationship between hardness and strength is needed in production.
1. Brinell Hardness (HB): A hardened steel ball of a certain size (typically 10mm in diameter) is pressed into the material surface under a certain load (generally 3000kg). After a period of time, the ratio of the load to the area of the indentation is the Brinell hardness value (HB), expressed in kgf/mm² (N/mm²).
2. 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 120° apex angle or a steel ball with a diameter of 1.59 or 3.18mm, pressed into the surface of the material under a certain load. The hardness of the material is determined by the depth of the indentation. Depending on the hardness of the test material, there are three different cases:
HRA: Hardness obtained using a 60kg load and a diamond cone indenter; used for materials with extremely high hardness (such as cemented carbide).
HRB: Hardness obtained using a 100kg load and a 1.58mm diameter hardened steel ball; used for materials with relatively low hardness (such as annealed steel and cast iron).
HRC: Hardness obtained using a 150kg load and a diamond cone indenter; used for materials with very high hardness.
3. Vickers Hardness (HV): A diamond square cone indenter with a 136° apex angle is pressed into the material surface under a load of up to 120kg. The Vickers hardness value (HV) is obtained by dividing the load value by the surface area of the indentation.
