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Hardness is the ability of a material to resist penetration of a hard object into its surface.It is one of the important properties of metal materials.Generally, the higher the hardness, the better the wear resistance.Common hardness indicators are brinell hardness, rockwell hardness and vickers hardness.
Brinell hardness (HB)
A hardened steel ball of a certain size (usually 10mm in diameter) is pressed against the surface of the material and a load (usually 3000kg) is applied for a period of time.After removing the load, the ratio of the load to the indentation area is brinell hardness.HB), in kilograms force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB> 450 or sample is too small, brinell hardness test should not be used instead of rockwell hardness tester.It USES a diamond cone with a top Angle of 120° or a steel ball with diameters of 1.59 and 3.18 mm, which is pressed into the surface of the material to be tested under a certain load and determines the hardness of the material from the depth of indentation.According to the hardness of the tested material, it is represented by three different scales:
HRA: hardness achieved by using a 60kg load and a diamond conical head with extremely hard materials such as cemented carbide.
HRB: hardened steel ball, load 100kg, diameter 1.58mm.Hardness is used for materials with lower hardness (such as annealed steel, cast iron, etc.).Precision CNC lathe machining bolt hardness
HRC: high hardness materials (such as hardened steel) obtained with 150kg load and diamond conical head.
3 vickers hardness (HV)
The material surface is pressed into the material surface with a 120kg or less load and a diamond cone press with a top Angle of 136°.The surface area of the material indentation pit divided by the load, that is, the vickers hardness number (HV).
As can be seen from the above, vickers hardness is one of the surface hardness.It has a conversion relationship with other hardness units.
Hardness is refers to the surface hardness, the material interior has no hardness requirements.Only mechanical properties (tensile strength, yield strength and impact toughness).
How does GB/T 3098.1-2000 have no surface hardness?5.6 does not indicate surface hardness?The surface hardness should not be higher than the core hardness of 30 vickers (about 3 HRC).Surface grade 10.9 hardness should not be greater than 390hv0.3.As for surface hardness requirements, it is a low performance grade, such as 3.6 4.6 4.8 5.6 5.8 6.8.Since there is no heat treatment, there is no requirement, as the hardness of the surface is mainly cold or baked.Post stress hardness.
When testing the hardness of bolts, bolts without heat treatment.Only an acceptable surface hardness is required.If it is a heat treated bolt, it should be hardened on the surface without cutting the diameter. The surface hardness test is 1/2 r.Where the hardness is up to standard.
It has a core with a surface, the surface is the vickers hardness or the surface rockwell hardness after removing the surface rust, and the core is removed from the surface and the core is 1/2 diameter after removing the part.2 hardness, the difference between the two hardness can not exceed 30HV, surface higher than 30HV indicates surface carburizing, is not allowed, if the surface is lower than 30HV, surface decarburization is not allowed.Take a closer look at this 3098.