Tempering Hollomon-Jaffe Parameter Calculator
The Hollomon-Jaffe parameter lets a metallurgist trade time against temperature when tempering steel. If a furnace is down or a load must be finished quickly, this tool estimates an equivalent cycle that produces similar softening.
Your numbers
Used to find the temperature that gives the same parameter in this time.
About 20 for many carbon and low alloy steels with time in hours. Use your alloy's published value when known.
Your results
Equivalence is an empirical aid for similar steels and tempering ranges. Always confirm hardness on a test coupon, and follow your controlled specification for the production cycle.
Equivalent temperature vs tempering time
Sweeps Target time for temperature solve from 0.25 to 8, holding your other inputs fixed.
Keep heat treat records searchable
Optional: a short review of how furnace cycles and test results could be linked to lots in your ERP.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the proven tempering temperature and time, then either a different temperature to learn the new time, or a target time to learn the temperature. The parameter P stays the same, so any pair with the same P should give approximately the same hardness for a given steel.
- Use hours for time and degrees Celsius for temperature.
- Keep the alternative temperature within the same tempering range.
- Confirm with a hardness test on a sample.
The method behind it
The parameter is P = T x (C + log10 t), with T in kelvin and t in hours. C is a material constant, around 20 for many steels. Because tempering is diffusion controlled, a small drop in temperature requires a much longer time for the same result: the relationship is logarithmic in time and linear in temperature. The tool solves for t at a second temperature, or for T at a chosen time.
Reading the result and common mistakes
For the default 600 deg C for 2 hours, tempering at 560 deg C needs roughly 19 hours, which shows how steep the trade is. Moving up in temperature shortens time but increases the risk of overshoot and temper embrittlement in susceptible steels. Do not use the equivalence across ranges that cross a secondary hardening or embrittlement zone.
- Applying the result to steels with strong secondary hardening.
- Entering minutes instead of hours.
- Ignoring furnace load heat-up time in the true time at temperature.
- Skipping the hardness check after a changed cycle.
Frequently Asked Questions
What is the Hollomon-Jaffe parameter?
It is a time-temperature parameter, P = T x (C + log10 t), used to compare tempering cycles. Two cycles with the same P produce about the same hardness in a given steel. It is similar in form to the Larson-Miller parameter used for creep.
What value of C should I use?
A value near 20 with time in hours is common for many carbon and low alloy steels. Alloy steels may differ, and published curves for your grade are better. If you have two hardness-matched cycles, you can back out C.
Is the time the total cycle time?
No, it is time at temperature, measured once the load core has reached the setpoint. Heat-up time in a dense load can be significant, so confirm the thermocouple placement and soak definition in your procedure.
Can I change a customer-approved cycle with this?
Only if the customer specification and your process approval allow it. Treat the tool as an engineering estimate, then qualify the new cycle with hardness and mechanical testing and record the change through your normal controls.
If heat treat cycles and certifications are stored in your ERP or QMS, we can discuss how to make them searchable for the shop. The calculator is free either way.
Related Tools
Carburizing Case Depth and Time Calculator
Estimate effective case depth for a carburizing temperature and time using a square-root diffusion model, or solve for the time needed for a target depth.
Industry TemplatesFoundry Heat and Pour Log Template
Fill in a one-page heat record covering alloy, furnace, temperatures, chemistry checks, treatment, molds poured and approvals, then export it.
Industry TemplatesUpset Forging Stock Length, Strain and Final Diameter Calculator
Enter bar diameter, stock length and target height to get final diameter, upset ratio, true strain and whether the stock exceeds the 3D buckling rule.
Industry TemplatesForging Billet Weight and Flash Allowance Calculator
Work out billet weight, bar cut length and material utilization from finished forging volume, flash percentage, scale loss and shear loss.
More Discrete Manufacturing tools
See all- OEE Calculator (Overall Equipment Effectiveness)
- Scrap Rate Cost Calculator
- Takt Time Calculator
- Cycle Time & Capacity Calculator
- Inventory Carrying Cost Calculator
- Economic Order Quantity (EOQ) Calculator
- MRP Nervousness Assessment
- Production Scheduling Maturity Assessment
- Shop Floor Digitization Scorecard