Estimate a preliminary diffusion-based case depth from treatment time, temperature and an assumed effective diffusion coefficient.
The estimator uses a simplified characteristic diffusion-distance relationship:
where x is characteristic diffusion depth, k is the selected model factor, D is the effective diffusion coefficient and t is treatment time in seconds.
Because diffusion coefficients depend strongly on temperature and material chemistry, the value entered here is treated as an effective average for the selected treatment.
Diffusion in steel is strongly temperature dependent. As temperature rises, atoms generally have greater mobility and the effective diffusion coefficient increases.
This means that a relatively small change in treatment temperature can have a substantial effect on the diffusion depth achieved during the same treatment time.
In a simplified diffusion model, characteristic diffusion distance increases approximately with the square root of time rather than directly with time.
Consequently, doubling treatment time does not normally double the characteristic diffusion depth. Approximately four times the time would be required to produce twice the characteristic diffusion distance when all other assumptions remain constant.
| Process | Primary Diffusing Element | Typical Purpose |
|---|---|---|
| Carburizing | Carbon | Hard wear-resistant surface with tough core |
| Carbonitriding | Carbon + nitrogen | Shallow hardened case on suitable components |
| Nitriding | Nitrogen | Hard surface with limited dimensional change |
| Gas carburizing | Carbon | Controlled carbon enrichment at elevated temperature |
The present estimator uses a generic diffusion model and does not separately solve the atmosphere/surface-reaction boundary condition for each process.
Case depth can be reported using different definitions. Effective case depth is commonly based on a specified hardness criterion, while a diffusion profile describes how concentration changes from the surface into the core.
Therefore, the characteristic diffusion distance produced by this tool should not automatically be interpreted as a certified effective case depth measured by hardness testing.
This tool is most useful for comparing the direction of changes in treatment time, temperature and diffusion assumptions. For example, increasing time or increasing the effective diffusion coefficient increases the estimated characteristic depth.
For production furnace design or specification work, use experimentally validated diffusion data and the actual carbon-potential profile rather than relying solely on this simplified model.
This estimator does not solve the full Fick's-law concentration profile with a changing surface concentration. It also does not model temperature-dependent diffusion throughout the cycle, carbon-potential changes, alloy-carbide effects, surface reaction kinetics or phase transformations.
It is therefore a preliminary engineering screening tool, not a substitute for a validated carburizing simulation, process specification or laboratory measurement.
What is case hardening depth? It is the depth below the surface affected by a case-hardening process, with the exact reported depth depending on the concentration or hardness criterion being used.
Does longer carburizing produce a deeper case? Generally yes. Under comparable conditions, characteristic diffusion distance increases approximately with the square root of treatment time.
Does higher temperature increase case depth? Generally yes because atomic diffusion becomes faster as temperature increases, although actual process limits and metallurgical effects must also be considered.
Why is the diffusion coefficient important? The diffusion coefficient represents how rapidly the diffusing species moves through the material. It is strongly dependent on temperature and material chemistry.
Can this predict exact carburized case depth? No. It provides a simplified characteristic diffusion estimate. Actual effective case depth should be established using validated process data and measurement.
What is the difference between diffusion depth and effective case depth? Diffusion depth describes a concentration-related penetration scale, while effective case depth is normally tied to a specified hardness criterion.