# Hollomon–Jaffe parameter

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The Hollomon–Jaffe parameter, or HP, describes the effect of a heat treatment at a temperature for a certain time.[1]

## Effect

The effect of the heat treatment depends on its temperature and its time. The same effect can be achieved with a low temperature and a long holding time, or with a higher temperature and a short holding time.

## Formula

In the Hollomon–Jaffe parameter, This exchangeability of time and temperature can be described by the following formula:

$H_p = \frac {(273.15 + T)}{1000} \cdot (C + \log(t))$

This formula is not consistent concerning the units; the parameters must be entered in a certain manner. T is in degrees Celsius. The argument of the logarithmic function has the unit hours. C is a parameter unique to the material used. The Hollomon parameter itself is unitless and realistic numeric values vary between 15 and 21.

$H_p = T (C + \log(t)) \,$

where T is in kilokelvins, t is in hours, and C is the same as above.