Hardness:

Hardness is the property of a material which enables it to resist plastic deformation, indentation, penetration, and scratching.   Thus, hardness is important from an engineering standpoint since resistance to wear through either friction or erosion through oil, steam, and water commonly increases along with hardness.

Hardness tests serve an important required in organization even by they do not measure a unique quality which could be termed hardness. A test is empirical, based on observation and experiments, rather than fundamental theory.  Its chief value is as an inspection device that is able to detect certain differences in material while they arise even by these differences might be undefinable.  For instance, two lots of material which have the similar hardness might or might not be alike, but if their hardness is different than the materials certainly are not alike.

Various methods have been established for hardness testing.  Those most frequent used are Rockwell, Brinell, Vickers, Sclerscope, Tukon, and the files test.  A first four are based on indentation tests and the fifth on the rebound height of a diamond-tipped metallic hammer. The file test establishes the features of how well a file takes a bite on the material.

As a conclude of several tests, comparisons have been prepared using formulas, tables, and graphs which display the relationships among the results of several hardness tests of specific alloys. There is, thus, no exact mathematical relation among any two of the methods.  For this purpose, the conclusion of one category of hardness test converted to readings of another category should carry the notation "converted from for instance "352 Brinell converted from Rockwell C-38".

Other convenient conversion is which of Brinell hardness to ultimate tensile strength. For tempered and quenched steel, the tensile strength (psi) is about 500 times the Brinell hardness number (generates the strength is not over 200,000 psi).