There are three commonly used indexes for tool hardness: Rockwell hardness, Brinell hardness and Vickers hardness.
1. Brinell hardness（HB）
With a certain load (generally 3000KG), a hardened steel ball of a certain size (generally 10mm in diameter) is pressed into the surface of the material, after holding 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), and the unit is kgf/mm2 (N/mm2).
2. Rockwell hardness（HR）
When HB>450 or the sample is too small, the Brinell hardness test can not be used and the Rockwell hardness can be changed. 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 material to be tested 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 divided into three different scales to express:
HRA: is the hardness obtained by using 60KG load and diamond cone indenter, used for extremely hard materials (such as carbide, etc.)
HRB: Hardened steel balls with a load of 100KG and a diameter of 1.58mm are used to obtain the hardness, which is used for materials with lower hardness (such as annealed steel, cast iron, etc.
HRC: It is the hardness obtained by using 150KG load and diamond cone indenter, which is used for materials with high hardness (such as quenched steel, etc.).
3. Vickers hardness（HV）
Use a load within 120KG and a diamond square cone indenter with an apex angle of 136° to press into the material surface, and divide the surface area of the material indentation pit by the load value, which is the Vickers hardness HV value (kgf/mm2).
4. Hardness & Material Composition & Heat Treatment Process
Under the same heat treatment process, the higher the carbon content of the material, the higher the hardness of the material. Corresponding to the same material, the hardness levels caused by the process are quenching, normalizing, and annealing.
5. The Range of Application
Each Rockwell hardness scale has a usable range, which is easily determined from the graduations on the hardness scale dial.
The range of application of different Rockwell hardness scales (excluding superficial Rockwell hardness scales) is as follows:
6. The hardness of Ouda Knife
Our kitchen knife blade is made of high-quality martensitic stainless steel. Martensitic stainless steel has the highest hardness. After quenching and tempering, the hardness reaches 56HRC. The carbon-chromium ratio is meticulous, and the hardness and toughness are balanced efficiently. Manual V-shaped cutting edge, sharp cutting edge, comfortable cutting, save worry and effort.
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