Carburizing Case Depth and Time Calculator
Carburizing depth grows with the square root of time and rises quickly with temperature. This calculator uses that diffusion relationship to estimate case depth for a cycle or the hours needed to reach a depth target.
Your numbers
About 0.025 inch per root hour is the commonly quoted figure for 925 deg C gas carburizing; calibrate with your furnace data.
Typically about 130 to 150 for carbon in austenite.
Your results
Diffusion models give an estimate only. Actual depth depends on carbon potential, steel grade, load density, quench and the hardness criterion used. Confirm with test coupons and cross-section hardness traverses.
Case depth vs time at temperature
Sweeps Time at carburizing temperature from 1 to 24, holding your other inputs fixed.
Capture furnace recipes in your ERP
Optional: a short review of how heat treat recipes and results could attach to work orders.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Set the carburizing temperature and the hours at temperature. The tool estimates the depth. To plan a cycle, enter a target effective case depth and read the hours needed. Adjust the reference constant after comparing the estimate with your coupon results, so the model matches your furnace.
- Count only time at carburizing temperature, not heat-up.
- Keep carbon potential in the range your procedure sets.
- Use effective case depth to the hardness your drawing names.
The method behind it
Carbon diffusion follows depth proportional to the square root of D x t, and the diffusion coefficient D follows an Arrhenius law with temperature. The tool uses a reference of about 0.635 mm per root hour at 925 deg C, the familiar 0.025 inch figure, and scales it with the activation energy. At 925 deg C for 8 hours it gives about 1.8 mm. Higher temperature shortens time but increases grain growth and distortion risk.
Reading the result and common mistakes
Because depth rises with the square root of time, doubling the cycle adds only about 41 percent more depth, which the chart makes clear. Going hotter often saves more than extending the cycle, but only if the steel and fixtures tolerate it. Carbon potential at the surface also limits what is possible.
- Assuming depth is linear with time.
- Mixing total case depth and effective case depth.
- Ignoring the diffusion step after boost cycles.
- Using one constant for all steel grades.
Frequently Asked Questions
Why does case depth go with the square root of time?
Diffusion is a gradient-driven process, so the penetration distance scales with the square root of the diffusion coefficient times time. Doubling the time increases depth by about 41 percent rather than doubling it.
What is effective case depth?
It is the depth from the surface to a specified hardness, commonly 50 HRC or 550 HV, though specifications vary. Total case depth extends further, to where the core carbon level is reached. Always match the definition on the drawing.
How accurate is this estimate?
Treat it as plus or minus 15 to 25 percent. Carbon potential, steel alloy, load geometry and quench all matter. After a few coupons you can tune the reference constant to your furnace and the model becomes more useful.
Is it valid for vacuum carburizing?
The diffusion relationship is similar, but vacuum low-pressure carburizing uses boost and diffuse pulses that change the surface carbon history. Use the supplier's simulation for vacuum recipes and use this tool for rough planning only.
If your heat treat shop schedules loads and certifications in an ERP or MES, we can discuss capturing furnace recipes next to the work order. The calculator itself needs no signup.
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