Briefly, Hardness Test is the resistance of a material to a permanent mark. It is important to remember that hardness is an empirical test and not a material property. For this reason, there are many hardness tests that will give a different hardness value for the same piece of material. Therefore, hardness is a dependent test method and each test result must have a label indicating the test method used.
Nevertheless, hardness is often used to characterize materials and determine whether they are suitable for their intended use. The hardness tests described in this chapter all involve the use of a specially shaped drill bit, much harder than the test specimen, which is pressed against the surface of the specimen with a specific force. The depth or size of the notch is measured to determine the hardness value.
Why is a Hardness Test Performed?
Easy to implement,
Fast – 1 – 30 seconds
Relatively cheaper
Visually, it can be applied to parts of all shapes and sizes,
Hardness Scales
There are five basic hardness scales:
Brinell – HB
Knoop – HK
Rockwell – HR
Shore – HS
Vickers – HV
Each of these scales uses a specially shaped diamond, carbide or hardened steel drill bit that is pressed into the material with a specific force using a specific test procedure. Hardness values are determined by measuring the depth of penetration of the insert. All scales are arranged so that the hardness values increase as the material hardens. Hardness values are reported using an appropriate symbol, such as HR, HV, HK, indicating the test scale performed.
Five Determining Factors
The following five factors can be used to determine the appropriate hardness test for your application:
Material – Grain size, metal, rubber, etc.
Approximate Hardness – Hard steel, rubber, etc.
Shape – Thickness, size, etc.
Heat Treatment – Fully or surface hardened, annealed
Production Requirements – Sample or 100%
APPLICATION STANDARDS
TS EN ISO 6506-1 : Metallic Materials – Brinell Hardness Test – Part 1: Test Method
TS EN ISO 6507-1 : Metallic Materials – Vickers Hardness Test – Part 1: Test Method
TS EN ISO 6508-1 : Metallic Materials – Rockwell Hardness Test – Part 1: Test Method
ASTM E18: Standard Test Methods for Rockwell Hardness of Metallic Materials
TS EN ISO 9015-1 : Destructive Tests on Welds in Metallic Materials-Hardness Test-Part 1: Hardness Test in Arc Welded Joints
ASTM E 92 : Standard Test Method for Vickers Hardness of Metallic Materials