How do you calculate carburising case depth?

Carburising case depth is calculated using the Harris diffusion equation: d = K × √t, where d is the case depth in mm, t is the carburising time in hours, and K is a temperature-dependent constant. At 920°C, K ≈ 0.5 for effective case depth. A more accurate version uses: d = C × √(D × t), where D is the diffusion coefficient for carbon in austenite at the process temperature.

What is the difference between effective and total case depth?

Effective case depth (ECD) is measured to the point where hardness falls to a specified threshold — typically 550 HV (about 52 HRC) per ISO 2639. Total case depth (TCD) is measured to the point where no compositional difference from the core can be detected. ECD is always shallower than TCD — for a typical gas carburising process, ECD is approximately 60–70% of TCD.

Case Depth Calculator — Carburising & Nitriding Depth Prediction

Carburising Case Depth Predictor

Process Temperature (°C)

920

Carburising Time (hrs)

4.5

Carbon Potential Cp

0.85

Effective Case Depth

— mm

Total Case Depth

— mm

What the Calculator Predicts

Effective case depth (ECD) to 550 HV / ISO 2639 criterion
Total case depth (TCD) from surface composition gradient
Required time at temperature for a target case depth
Carbon concentration profile across the case depth
Nitriding case depth — compound layer and diffusion zone
Carbonitriding depth with combined C+N diffusion

Typical Case Depths by Process

Process	ECD Range	Temp
Gas carburising	0.5–3.0 mm	900–950°C
Vacuum carburising	0.3–2.5 mm	900–1050°C
Carbonitriding	0.05–0.75 mm	800–875°C
Gas nitriding	0.1–0.6 mm	480–530°C
Plasma nitriding	0.05–0.8 mm	450–560°C
Salt bath nitriding	0.05–0.3 mm	500–580°C

Case Depth Prediction in Gas Carburising

Carbon case depth in gas carburising follows Fick's second law of diffusion. The simplified Harris equation — d = K × √t — provides a practical engineering estimate, where K is a temperature-dependent empirical constant. At 920°C, K ≈ 0.5 mm/√hr for effective case depth. Higher temperatures produce deeper cases in less time but carry higher distortion and grain growth risk.

Our calculator uses the full diffusion model (temperature-dependent diffusion coefficient, surface concentration from carbon potential, and base steel composition) to generate a carbon concentration profile and predict both ECD (to 550 HV criterion per ISO 2639) and TCD. The result can be used for process qualification, route card planning, and specification compliance.

Predict Case Depth Free

Enter your temperature, time, and carbon potential — get ECD and TCD predictions with a carbon concentration profile.

Case Depth Calculator

What the Calculator Predicts

Typical Case Depths by Process

Case Depth Prediction in Gas Carburising

Predict Case Depth Free

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