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Hardness is a surface property where indentation, scratching or wear is resisted.
The higher the hardness the more resistant is the surface, and the more difficult surface operations such as cutting and machining are.
Testing the hardness of steels can be used an indication of how easily they can be manipulated, (formed, machined etc.), and how they will perform mechanically.
Common tests for hardness in metals involve measuring the resistance to indentation by a hardened steel or diamond ball, cone or pyramid.
The common test methods include: –
The hardness figures do not have units. They are an index, based on either the cross-section of the indentation made, measured after the test, or the depth of indentor travel into the metal surface.
The hardness figure is followed by a code indicating the test method.
The Brinell and Vickers methods have been used historically in the UK, the Brinell method for softened steels, and Vickers method for either softened or hardened steels.
In these tests the ‘diameter’ of the impression is measured.
The Rockwell method was first introduced in the US.
These methods assess the hardness by measuring the depth of indentor penetration.
The B scale is used for softened steels and the C scale for hardened steels.
Other scales are also available. These include scales A, D, E, F, G H, K, as well as ‘superficial test’ scales HR15N, HR30N, HR45N (cone indentor) and HR15T, HR30T, HR45T (ball indentor).
Normally the B and C scales are used on stainless steels, B for softened steel and C for hardened steel.
There are several hardness scale conversion systems, including BS 860 and ASTM E140.
The table shows a set of values that has been used for stainless steels and also includes a tensile strength (UTS) comparison. The Rockwell B values are superimposed on this table using an approximation from ASTM E140 Table5, which compares Rockwell B and Brinell.
Comparison tables should only be used as a guide. The figures shown are not equivalents and BSSA accepts no responsibility of the accuracy of the data. In any case of doubt or dispute, values using the actual test methods should be used rather than converted table values.
|Brinell Hardness (HB)||Vickers Hardness (HV)||Rockwell (HRB)||Rockwell (HRC)||UTS (N/mm2)|
Other sources of hardness equivalent tables are: