snipped-for-privacy@wt.net (Chris North) wrote in message

I need help in finding some information on tempering. The application is tempering Cr-Mo steels, ... and section sizes are
small enough that transformation to martensite is achieved fully.
What I need is a way to predict final hardness based on tempering
time and temperatures. The object is to minimize the time and still
achieve acceptable hardness (as well as tensile and impact)
properties.
From school, I remember Larsen-Miller relationship P=T*(log(t)+C), but
this was years ago and my old texts were lost over the years and all I
can recall is the equation and not how to use it. Are there any
better correlations out there? Maybe one based on chemistry? Any
help would be appreciated.
Thanks,

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Chris:

You're more than halfway there since you remembered there is an equation. If I recall correctly, Larson and Miller borrowed the tempering parameter from Hollomon and Jaffee.

The tempering parameter, P is defined by the equation P = T*(A + log(t)) where T is the absolute temperature in Kelvin, t is the time in hours, and A is a constant about twenty. Hardness (or yield or tensile strength) is supposed to depend on P. So, for the same steel a series of points at equal time and different temperatures could be used to develop a master curve.

G. Krauss's book STEELS: Heat Treatment and Processing Principles, ASM International, 1990 discusses the tempering parameter on pages 215-216.

Use of the tempering parameter is discussed in more detail in the older book Ferrous Metallurgical Design by J. H. Hollomon and L. D. Jaffe, Wiley & Sons, New York, 1947 They say that the constant A depends linearly on carbon content, with A = 21.1875 - 5.625*(%C) For short soak times you may need to get fancier and include the heatup. You have to integrate. I vaguely recall that S.L. Semiatin showed how to do this in another ASM book on induction heat treating. For modified 4130 steels with 1%Cr, 0.75%Mo and 0.025% Nb containing 0.15% to 0.37% carbon, and A varying with carbon content as previously shown, the yield strength in MPa depends on P as (see p. 364 of Hydrogen Effects in Metals, Met Soc. AIME, Warrendale, 1981):

YS(MPa) = 23168 - 2198

Pittsburgh Pete

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I need help in finding some information on tempering. The application is tempering Cr-Mo steels, ... and section sizes are

----------------------------------------------------------

Chris:

You're more than halfway there since you remembered there is an equation. If I recall correctly, Larson and Miller borrowed the tempering parameter from Hollomon and Jaffee.

The tempering parameter, P is defined by the equation P = T*(A + log(t)) where T is the absolute temperature in Kelvin, t is the time in hours, and A is a constant about twenty. Hardness (or yield or tensile strength) is supposed to depend on P. So, for the same steel a series of points at equal time and different temperatures could be used to develop a master curve.

G. Krauss's book STEELS: Heat Treatment and Processing Principles, ASM International, 1990 discusses the tempering parameter on pages 215-216.

Use of the tempering parameter is discussed in more detail in the older book Ferrous Metallurgical Design by J. H. Hollomon and L. D. Jaffe, Wiley & Sons, New York, 1947 They say that the constant A depends linearly on carbon content, with A = 21.1875 - 5.625*(%C) For short soak times you may need to get fancier and include the heatup. You have to integrate. I vaguely recall that S.L. Semiatin showed how to do this in another ASM book on induction heat treating. For modified 4130 steels with 1%Cr, 0.75%Mo and 0.025% Nb containing 0.15% to 0.37% carbon, and A varying with carbon content as previously shown, the yield strength in MPa depends on P as (see p. 364 of Hydrogen Effects in Metals, Met Soc. AIME, Warrendale, 1981):

YS(MPa) = 23168 - 2198

***P + 53.519***P*PPittsburgh Pete

INFAMOUS USS DISCLAIMER

Note: It is understood that this material is intended for general information only and should not be used in relation to any specific application without independent examination and verification of its applicability and suitability by professionally qualified personnel. Those making use thereof or relying thereon assume all risk and liability arising from such use or reliance.

ENGLISH TRANSLATION OF DISCLAIMER

We don't believe what we write, and neither should you. Information furnished to you is for topical (external) use only. This information may not be worth any more than either a groundhog turd, or what you paid for it (nothing). The author may not even have been either sane or sober when he wrote it down. Don't worry, be happy.