What is the Hardening Case Depth?

In powder‑coating and heat‑treatment processes, the case depth (often called the hardened layer thickness) is a critical parameter that determines wear resistance and fatigue life of a component.
 

The depth is primarily governed by the diffusion of carbon (or other alloying elements) into the steel substrate during the carburising step.

The diffusion rate follows Fick’s laws and is highly temperature dependent; higher temperatures accelerate atom mobility, while longer exposure times allow the diffusion front to travel further into the material.

Engineers therefore balance temperature and time to achieve a target case depth without compromising dimensional tolerances. Empirical models translate these physical principles into practical equations.

A common representation relates case depth (d) to the square‑root of time (t) multiplied by an exponential term that captures the Arrhenius temperature effect.

This provides a quick, yet reasonably accurate, estimate for process planning.