Vickers

Vickers Hardness Testing

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

Conversion Table

Application

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.

Vickers Indent Spacing

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.

Diagonal Width

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.

Vickers Test Method table

Surface Preparation

Macro hardness test

  • ground

Micro hardness test

  • mechanically polished
  • electro-polished

Loads

In general use the highest possible load. A few applications, however, call for special loads.

  • Avoid tests producing diagonal lengths less than 20 μm, otherwise the measurement inaccuracy will be too high.
  • The difference between the two Vickers diagonal lengths should be max. +/-5%, otherwise the test should be discarded.
Vickers Loads table
  • Indentation time 10-15 seconds
  • Sample Thickness ISO: Diagonal length of indentation x 1.5 Indentation time 10-15 seconds
  • Sample thickness ASTM: At least 10 times the depth of indentation

 

Applicable standards

Applicable Standards

  • ASTM E384 – micro and macro ranges
  • ISO 6507 – micro and macro ranges
  • JIS Z 2244

Case Hardness Depth (CHD) measurement

Surface Hardness

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 centre.

The hardness progression is plotted in 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 "Hardnes Limit"

  • Applicable Standards: EN ISO 2639 / EN 10328 / ISO 3754 / DIN 50190-3

Different ways of calculating CHD

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 between three ways of calculating the hardness limit:

1. Carburised 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 50HV 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.

Jominy Testing

Jominy Testing

The Jominy Test (End Quench Test) is a standardised test procedure used to determine the hardenability of steel.

  • The procedure is described in the following standards: ASTM A255 / ISO 642 / DIN 50191 / BS 4437

The Jominy Test involves heating a cylindrical steel test piece to an austenitizing temperature (~980°–1010°C) and quenching (cooling) from one end with a controlled and standardised jet of water. After quenching, the hardness is measured at intervals taken from the quenched end. The test method used is either HRC or HV30.

The hardness variation along the test surface is a result of microstructural variation that arises as the cooling rate decreases with the distance from the quenched end. The harder the material is at a given distance from the end, the higher the hardenability of the steel.

Go to Rockwell Method
Hardness Testing on Welds

Hardness testing on welds

Hardness testing of welds is a subgroup of VickersThe 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 are often made at a given distance from the sample edge or from top of the weld. The progression of the hardness values can then be plotted in a graph.

  • The methods used are typically HV5 and HV10 and the applicable standards referred to are often the ISO 9015-1/-2.

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