Hardenability is defined as the ability of steel to develop its maximum hardness when subjected to the normal hardening heating and quenching cycle. High hardenability means that the steel hardens more nearly throughout rather than just at the surface. In order words, good hardenability is indicated by a greater depth of hardening below the surface.
Often a confusion arises about the meaning of hardening power and hardenability. It may be remembered that hardening power refers to the maximum haardness obtainable with steel of given composition while hardenability refers to the depth of hardening in a given thickness of steel. Only the carbon content affects the maximum hardness that can be realised with any steel. High carbon content makes more carbon and iron carbide available to distort the martensitic structure and consequently allows higher hardness. The hardenability of a steel becomes greater as the percentage of carbon increases and is further improved by the addition of such alloying elements as manganese, nickel, chromium, molybdenum and vanadium, and by increase in the austenite grain size.
The factors which affect the depth of hardening of steel components are given below:
- Hardenability of the steel from which the component is made.
- Severity of quench used.
- Size and shape of the piece.
- Surface condition and the austenite grain size.
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