NTB SpecPro

Tempering parameter calculator

NTB SpecPro special-process quality control software logo NTBSpecProSPECIAL PROCESS SOLUTIONS
Sign in Get started

Free tool · Heat treatment

Tempering parameter calculator

Use the Hollomon-Jaffe parameter P = T(K) × (C + log t) to check whether two temperature–time pairs are equivalent: P is calculated for a known tempering cycle and the time that gives about the same effect at another temperature is found. Everything runs in your browser.

Also available in: Türkçe · العربية

Parameter P = T(K) × (C + log t)–
P / 1000–
Equivalent time at T₂– h

P = (T + 273.15) × (C + log₁₀ t), t in hours · t₂ = 10^(P / (T₂ + 273.15) − C)

The constant C depends on the steel; the literature gives about 20 for plain carbon and low-alloy steels (19.5 in the original work), slightly lower as carbon rises. The parameter was derived for tempering of quenched steel; it is not used for aluminium ageing or precipitation hardening. The result is an approximate match for the same hardness; verify with hardness and, where needed, microstructure.

For information only; the material specification, the AMS/EN heat treatment standard and the approved recipe govern. The final assessment rests with the responsible heat treatment engineer.

Let the app keep your furnace charts and hardness resultsThe Heat treatment module reads furnace charts, keeps hardness and microstructure records and prepares PDF reports for your audit file.
Try the Heat treatment module

Curious?

What is the tempering parameter for?In tempering, temperature and time act together: a longer time at a lower temperature and a shorter time at a higher temperature give similar hardness. The parameter condenses both into one number; it is used to check equivalence when the furnace programme changes or the time is extended for a thick part.
How do I choose the constant C?The common value is 20. It drops somewhat as carbon content rises (about 15–18 is used for high-carbon steels). If the material producer or the heat treatment specification gives a value, use that.
Can I use it for aluminium ageing?No. The Hollomon-Jaffe parameter was derived for tempering of quenched steel. Precipitation hardening of aluminium and nickel alloys follows different kinetics; the temperature–time windows in specifications such as AMS 2770/2774 are applied as written.
How should I keep the furnace record?The temperature–time curve (furnace chart), load map and hardness results are kept for every charge; they are the first records an auditor asks for. The Heat treatment module of the app reads a photo of the furnace chart and keeps hardness and microstructure records under the same charge.

Other free tools