The Jominy end-quench test which follows ASTM: A-255, is
used to measure the hardenability of steels. It consists on heating
of a standardized cylindrical specimen of material in test
(25.4 mmdiameter and 100.0 mmin length) until the austenitizing
temperature, and then cooling it at one end through of water in
order to induce the formation of the martensitic structure. After
that, the hardness is measured along the specimen at intervals of
1.59 mm between each measure. Obviously, the first measure presents
high values of hardness due to the formation of martensite by
high cooling water. Consequently, the hardness decreases in more
distant positions of the cooled surface, because in these points, the
cooling rates are lower resulting in the formation of phases such as
ferrite, pearlite and bainite.