## Vickers hardness test
The The hardness number is not really a true property of the material and is an empirical value that should be seen in conjunction with the experimental methods and hardness scale used. When doing the hardness tests the distance between indentations must be more than 2.5 indentation diameters apart to avoid interaction between the work-hardened regions. The yield strength of the material can be approximated as - .
where c is a constant determined by geometrical factors usually ranging between 2 and 4. ## Implementation
The Vickers hardness test uses a hardness of the material to be measured. The Vickers Pyramid Number (HV) is then determined by the ratio - ,
which can be approximated by evaluating the sine term to give - ,
where - .
The corresponding units of HV are then kilogram-force per square millimetre (kgf/mm²). To convert a Vickers hardness number in SI units (MPa or GPa) one needs to convert the force applied from kgf to newtons and the area from mm A practical method to convert HV to SI units: To convert HV to MPa multiply by 9.807To convert HV to GPa multiply by 0.009807Vickers hardness numbers are reported as -
**440**is the hardness number, -
**HV**gives the hardness scale (Vickers), -
**30**indicates the load used in kg.
## ExamplesSome HV values - Stainless Steels 140-180HV30 (316L & 347L stainless respectively)
- Carbon Steel 55-120HV5 (Note: load is different to that of stainless)
- Iron 30-80HV5
## References**^**Smithells Metals Reference Book, 8th Edition, chptr. 22
- Meyers and Chawla (1999). "Section 3.8",
*Mechanical Behavior of Materials*. Prentice Hall, Inc. - Vickers hardness test on Gordon England site.
## See also |

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Vickers_hardness_test". A list of authors is available in Wikipedia. |