The surface hardness is the hardness value measured directly on the surface of your component. This is a measure for the mechanical resistance with which the component opposes the mechanical intrusion of another body. Amongst other things, it is therefore a measure of resistance to abrasive wear.
During plasma nitriding, the surface hardness is determined using a Vickers hardness tester. Depending on the layer thickness and surface hardness, testing is performed with a variable load.
In addition to the required hardness value, the test process and the test force (in kilogram-force) is also specified on the drawing.
Example: Surface hardness 610 HV1
Here, 610 is the hardness value, HV is the Vickers hardness test process and 1 is the test force of 1 kilogram-force.
The table provides an indication about which load is suitable for the test.
The core hardness refers to the hardness which is measured in the core of the component. The core hardness is often measured in the metallographic cut.
For flawless nitriding, the core hardness should not change substantially compared to the core hardness of the untreated component.
The core hardness is also measured based on the Vickers process. The drawing specification is made by specifying a hardness value and the test load. A minimum and a maximum hardness value can be specified within which the core hardness should be.
The specification of a maximum hardness is useful if excessively deep nitriding is to be ruled out. The specification of a minimum hardness is primarily important for hardened materials if tempering is to be ruled out through the nitriding process.
Layer thickness specifications:
For materials which form a compound layer, it can be useful to specify the thickness of the compound layer. The same applies to high-alloy materials which only form a diffusion layer. Depending on the application, a minimum layer thickness and, if necessary, also a maximum layer thickness are specified. The specification is in µm.
Example 1: Compound layer thickness (CLT): 5–15 µm
Example 2: Diffusion layer thickness (DS): 5–25 µm
Nitriding hardness depth:
The nitriding hardness depth (DIN 50190T3), abbreviated to NHD, is defined as the vertical distance from the surface of a nitrided workpiece to the point at which the hardness corresponds to a defined hardness value. This hardness value is referred to as the hardness limit. A common definition for the hardness limit is the following:
Hardness limit = core hardness + 50 HV
Rounding to 10 HV occurs here. Test forces deviating from HV 0.5 are possible in the range HV 0.3 to HV 2.