The Jominy Hardenability Curve is a graph that shows how the hardness of the steel sample varies along its length. The hardness of the sample after the Jominy end-quench test is important for determining the supportable hardenability, the ability of steel to harden at different distances from the surface during heat treatment of steel.

Key Features:

• Testing: In the Jominy test, one end of a heated steel sample is cooled down with a jet of water. Hardness testing is then performed at consistent intervals along the depth, away from the quenched end of the sample.
• Graph characteristics: The hardness values (usually Rockwell or Vickers hardness) are plotted on the vertical axis and distance away from the quenched end of the sample on the horizontal axis.
• Application: This graphic can help a manufacturer decide what grade of steel is best for specific application requirements of surface hardness or specific hardness at certain depths, such as in gear components, shafts, or axles.

The Jominy Hardenability Curve is valuable for all steel selections and the design of heat treatment. A steep curve indicates the steel has low hardenability (is hard only close to the surface), while a flat curve would show the steel hardness, or depth of hardness, was uniform. This information allows pressure, load, or high wear conditions on a component to have an adequate strength and wear resistance at depth and not just on the surface—these variables are very important for the high stress and load-carrying applications.