The Vickers Hardness (HV) is calculated by measuring the diagonal lengths of an indent left by introducing a diamond pyramid indenter with a given load into the specimen material. The loads used range from 10 gf (1 gf) up to 100 kgf. The Vickers test can be used to test all solid materials and is suitable for a wide range of applications.
Applicable Standards:
- ASTM E384 – micro and macro ranges
- ISO 6507 – micro and macro ranges
- JIS Z 2244
The Vickers test is a versatile method, with only one type of indenter and a broad load range. It is suitable for a wide range of applications to test all solid materials.
When performing a vickers hardness test, your indentation will deformate the surrounding material and alter its properties. In order to avoid misinterpretations of the perceived hardness, the standards therefore prescribe a certain distance between multiple indentations. For steel and copper, indentations have to be spaced with at least 3 diagonal widths, whereas for lead, zinc, aluminium and tin the indent spacing has to be at least 6 diagonal widths.
Please also observe that the minimum diagonal width, according to international standards, should preferably be at least 20 µm in order to ensure accurate reading of the indents. This for instance implies that CHD measurement using less than HV0.2 generally should be avoided, as it will produce indents smaller than 20 µm.
See the overview of the Vickers methods and the most common applications.
Macro Hardness Test
Micro hardness test
In general, use the highest possible load. A few applications, however, call for special loads.
A common application of hardness testing is the evaluation of the hardness depth of surface-hardened steels. This is done by performing a series of hardness impressions from the edge of the cross-sectioned sample towards the center.
The hardness progression is plotted on a graph, and the distance from the surface to the so-called hardness limit (HL) is calculated. In most cases, Vickers hardness tests are used in the micro hardness load range. In certain cases, Knoop can also be used.
Case Depth = Distance from "Surface" to "Hardness Limit"
There are different ways of determining the hardness limit and, thus, of calculating the CHD value. The procedure depends on the hardening process used. Generally, we distinguish among three ways of calculating the hardness limit:
1. Carburized or carbonitrided parts (EN ISO 2639)
Hardness Limit = 550 HV
CHD (Eht) = Distance from surface to a point where the hardness is 550 HV
2. Induction or flame-hardened parts (EN 10328, ISO 3754)
Hardness Limit = 80% x (minimum) surface hardness.
CHD (Rht) = Distance from surface to point where hardness is 80% of the (minimum) surface hardness.
3. Nitrided parts (DIN 50190-3)
Hardness Limit = Core Hardness + 50 HV.
CHD (Nht, NCD) = (Max.) Distance from the surface to the point where hardness is 50 HV above core hardness
Example of CHD Progression
CHD Measurement Displaying CHD-value of 0.95 mm at Hardness Limit of 550 HV1
When performing a hardness progression, please observe the rules for indent spacing.
NB: Edge retention is needed during the mechanical preparation of samples to ensure an accurate measurement of the case-hardened depth.
The Jominy Test (End Quench Test) is a standardized test procedure used to determine the hardenability of steel.
Hardness testing of welds is a subgroup of Vickers. The purpose of hardness testing on welds is to evaluate the strength of the weld. Particular focus is on the hardness around the heat-affected zone (HAZ). The hardness in and around the HAZ can help evaluate the brittleness of the weld and, thus, whether the weld has the desired strength.
A series of measurements in a given pattern is often made at a given distance from the sample edge or from the top of the weld. The progression of the hardness values can then be plotted on a graph.
