The Hollomon–Jaffe parameter (HP), also generally known as the Larson–Miller parameter,[1] describes the effect of a heat treatment at a temperature for a certain time.[2] This parameter is especially used to describe the tempering of steels, so that it is also called tempering parameter.
Effect[edit]
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[edit]
In the Hollomon–Jaffe parameter, this exchangeability of time and temperature can be described by the following formula:
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.
where T is in kilokelvins, t is in hours, and C is the same as above.
Holloman and Jaffe determined the value of C experimentally by plotting hardness versus tempering time for a series of tempering temperatures of interest and interpolating the data to obtain the time necessary to yield a number of different hardness values. This work was based on six different heats of plain carbon steels with carbon contents varying from 0.35%–1.15%. The value of C was found to vary somewhat for different steels and decrease linearly with the carbon content of a steel grade. Holloman and Jaffe proposed that C = 19.5 for carbon and alloy steels with carbon contents of 0.25%–0.4%; and C = 15 for tool steels with carbon contents of 0.9%–1.2%.[3]
See also[edit]
References[edit]
- ^ Hollomon, J.H.; Jaffe, L.D. (1945). "Time-temperatures relations in tempering steel". Transactions of the American Institute of Mining and Metallurgical Engineers. 162: 223–249.
- ^ Brooks, Charlie (1996). Principles of the heat treatment of plain carbon and low alloy steels. ASM International. p. 158. ISBN 0871705389.
- ^ Canale, L.C.F; Yao, X.; Gu, J.; Totten, G.E. (2008). "A historical overview of steel tempering parameters". International Journal of Microstructure and Materials Properties. 3 (4–5): 474–525. doi:10.1504/IJMMP.2008.022033.