These two concepts are the indexes to show the quenching capacity of steel in heat treatment, are the important basis for material selection heat treatment process formulation.

(1) Hardenability is the value of high hardness that steel can get under normal quenching conditions, it is the ability to obtain high low hardness when steel is quenched.

The main factor that determines the hardenability of steel is the carbon content of steel, but the alloy elements in steel have little effect on the hardenability. Therefore, the hardness values of carbon steel alloy steel with the same carbon content after quenching are generally similar.

(2) Hardenability refers to the depth of hardened layer that can be obtained when steel is quenched. This index is also related to the size, weight size of steel. Strictly speaking, hardenability is the inherent property of steel is determined by the internal factors of steel.

Hardenability of steel, also known as hardenability, refers to the ability to obtain the depth of hardened layer when steel is quenched. For workpieces with the same size different steel grades, after quenching under the same conditions, some can obtain martensite structure in the whole cross section, some can only obtain martensite structure within a certain thickness of the surface layer, some can obtain all martensite even in the outermost layer. It can be seen that the hardenability of different steels is different. The better the hardenability of steel is, the deeper the hardened layer is.

The actual depth of hardened layer of steel forgings during quenching is affected only by its own hardenability, but also by other external factors. If the cooling capacity of the quenching medium is strong (the actual hardening layer is deep if the cooling capacity of the medium is large) the size of the workpiece, the actual hardened layer thickness will be affected.

The concept of hardenability is different the concept of hardenability of steel. The hardenability of steel is usually measured by the depth of hardened layer obtained after quenching under certain conditions. Theoretically speaking, the depth of hardened layer should be the region with all martensite structure. However, in practical production, the depth the workpiece surface to the semi martensitic zone (martensite non martensitic structure accounts for 50% respectively) is generally defined as the depth of hardened layer.

There are many methods to determine the hardenability of steel, the critical diameter method end quenching method are commonly used.