Part Hardenability and Impact Factors

Hardening and then tempering undoubtedly give a steel part the best combination of strength and toughness. The depth at which a metal alloy can be hardened, also called hardenability is an aspect often weighed during the part design process.
Don’t confuse hardenability versus hardness, as they are not the same. Hardenability is impacted by many factors, including the material’s composition, size, and the quenching process.

Hardness vs Hardenability

Hardness and hardenability, while different, both detail essential information about a material.

Hardness is a material property that signifies an alloy’s resistance to penetration. Hardness is dependent mostly on a ferrous material’s carbon content, and a few other determining factors.

Hardenability signifies how deep the alloy can be hardened upon quenching after its exposure to heat treatment. The higher a part’s hardenability, the better it will stand up to heavy wear and other stresses during its intended application.

Factors Impacting Hardenability

The biggest determining factor of a part’s hardenability is its composition. Other factors, like the quenching process, will also impact the depth to which part is hardened.


All heat-treated alloys must contain carbon. A steel grade’s carbon content and it’s other alloying elements, help to determine the hardenability of the material.

When an iron-based metal or steel is heated, its crystal structure changes from ferrite to austenite before being transformed to martensite through the quenching process. By the addition of alloying agents such as manganese, molybdenum and vanadium it increases the hardenability of steel when it is phased to martensite.

The quick and focused nature of induction heat treating can control a part’s hardenability. A material that may through harden in a furnace process can be hardened just at the surface with controlled depth using induction heat treating. Unlike other types of heat treating, induction will harden the surface and leaving much of the internal material relatively ductile and flexible, this is ideal for shafts, spindles and axles.

The mass and shape of a part also impact hardenability. The more volume a part has, the more it will affect the cooling rate and the martensite transition process.


Proper and consistent quenching is essential to reach the right level of hardenability and the appropriate phase transition of the heat-treated part. The quenching medium, whether it be water, oil, or others, should be selected based on the alloy’s material characteristics.

As induction specialists, Zion’s team is experienced in delivering consistent part results with hardness and properties your customers need. Give us a call at 330-483-4650 or contact us to learn how we can strengthen your next project.

Ask the Experts: Heat Treating Q&A with President Bob Puls
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