Vickers Hardness Test Report

Vickers hardness test

Introduction

The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of the material. The Vickers hardness test follows the Brinell principle, in that an indenter of definite shape is pressed into the material to be tested, the load is removed, the diagonals of the resulting indentation are measured, and the hardness number is calculated by dividing the load by the surface area of indentation.

The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness.

This indenter thus has an angle across corners, or a so-called edge angle, of 148o 6’ 42.5”. The faces are highly polished, free from surface imperfections, and the point is sharp. The loads applied vary from 1 to 120 kg; the standard loads are 5, 10, 20, 30, 50, 100, and 120 kg. For most hardness testing, 50 kg is maximum.

The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the VICKERS PYRAMID NUMBER (HV) or DIAMOND PYRAMID HARDNESS (DPH). The hardness number can be converted into units of Pascals, but should not be confused with pressure , which also has units of Pascals. The Type equation here.hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not pressure.

To calculate Vickers hardness number using SI units one needs to convert the force applied from kilogram-force to Newtons by multiplying by 9.80665 (standard gravity) and dividing by a factor of 1000 to get the answer in GPa. This leads to the following equation that can be used to do any calculation directly.

HV=0.1891(F/d2)GPa

Where F is in N and d is in millimeters.

Vickers hardness numbers are reported as xxxHVyy, e.g.440HV30, or xxxHVyy/zz if duration of force differs from 10 s to 15 s, e.g.440HV30/20,

Where:

440 is the hardness number, HV gives the hardness scale (Vickers), 30 indicates the load used in kgf. 20 indicates the loading time if it differs from 10 s to 15 s

Vickers values are generally independent of the test force: they will come out the same for 500gf and 50kgf, as long as the force is at least 200 gf.

For thin samples indentation depth can be an issue due to substrate effects. As a rule of thumb the sample thickness should be kept greater than 2.5 times the indenter diameter. Alternatively indent depth can be calculated according to: h=d/2√2 tan(136o/2 )=d/7.0006’ Examples of HV values for various materials

MATERIAL VALUE

316L stainless steel 140HV30

347L stainless steel 180HV30

Carbon steel 55-120HV5 aIron 30-80HV5

Martensite 1000HV

diamond