Correlation between hardness and tensile strength of Engineering steels materials

 Ductility and brittleness: Ductility is ability to undergo plastic deformation under given increase in load to the extent of fracture. However Brittle materials experiences very little or almost zero plastic deformation when subjected to tensile load beyond elastic limit and fractured at fracture strength which is close to its elastic limit or yield point.

Generally, a material can be considered as brittle, if it is strained up to less than 5% at the point of its fracture. Schematic representation of ductile and brittle materials sustained to deformed at fracture point is shown in the sketch below. Though the brittle material has higher yield stress and tensile strength as compared to ductile, it is not tougher than ductile

As a rule of thumb for most of the steels, tensile strength  is related to following formula :

 1.Tensile strength ( psi) = 500* BHN

 2.Tensile strength ( MPa) = 3.45* BHN