Define Hardness, Hardenability and Brittleness

Hardness is a fundamental property which is closely related to strength. Hardness is usually defined in terms of the ability of a material to resist to scratching, abrasion, cutting, indentation , or penetration. It is important to note that the hardness of metal does not directly related to the hardenability of the metal.

Many methods are now in use for determining the hardness of a material. They are Brinell., Rockwell and Vickers.

Hardenability indicates the degree of hardness that can be imparted metal , particularly steel, by the process of hardening. It determines the depth and distribution of hardness induced by quenching. The hardenability of a metal is determined by a Jominy test to determine how well a metal hardens from the center of the metal to the interface of the metal. The Jominy test involves heating a test piece from the steel to an austenitising temperature and quenching from one end with a controlled and standardized jet of water. A metal that id capable of being hardened throughout its structure is said to have high hardenability.

The Brittleness of a material is the property of breaking without much permanent distortion. There are many materials which break or fail before much deformation takes place. Such materials are brittle , e.g., glass, cast iron, Therefore, a non-ductile material is said to be brittle material. Usually the tensile strength of brittle materials is only a fraction of their compressive strength.

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