Hardness indicates the ability of a material to resist pressing a hard object into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.
1. Brinell hardness (HB)
Press a hardened steel ball of a certain size (usually 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 the indentation area is the Brinell hardness value ( HB), in kilogram force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB>450 or the sample is too small, Brinell hardness test cannot be used and Rockwell hardness measurement should be used instead. It uses a diamond cone with a vertex angle of 120° or a steel ball with a diameter of 1.59mm 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 hardness of the test material, it can be expressed in three different scales:
HRA: It is the hardness obtained by using a 60kg load and a diamond cone indenter, and 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. It 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, and is used for materials with high hardness (such as hardened steel, etc.).
3 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 surface of the material, and divide the surface area of the indentation pit by the load value to obtain the Vickers hardness value (HV).
From the above introduction, we can see that Vickers hardness is one of surface hardness. There is a conversion relationship between it and other hardness units.
Hardness refers to the surface hardness, and there is no hardness requirement inside the material. Only mechanical properties are required (tensile strength, yield strength and impact toughness).
Why is there no surface hardness in GB/T 3098.1-2000? Doesn`t 5.6 indicate the surface hardness? The surface hardness should not be 30 Vickers hardness (about 3 HRC) higher than the core hardness. The surface of grade 10.9 The hardness should not be greater than 390HV0.3. As for those without surface hardness requirements, it is a low performance level, such as 3.6 4.6 4.8 5.6 5.8 6.8, because there is no heat treatment, so there is no requirement, because the hardness of the surface is mainly cold heading or baking turning The hardness produced by the subsequent stress.
When testing bolt hardness, bolts without heat treatment only need to make the surface hardness within the acceptable range. If it is a heat-treated bolt, it is necessary to cut a diameter of the surface to increase the hardness, and the hardness test is 1/2R on the surface. The hardness meets the standard.
It has a surface and a core. The surface refers to the Vickers or surface Rockwell hardness after removing the surface floating rust. The core should be 1/2 of the core after removing the 1/2 diameter long part 2, the difference between the two hardnesses cannot exceed 30 HV. If the surface is higher than 30HV, it means that the surface is carburized, which is not allowed. If the surface is lower than 30HV, it means that the surface is decarburized, which is also not allowed. Look at this 3098 carefully.
bolt hardness
2023 06/09