Calculating transition temperatures
Calculating transition temperatures
(OP)
I don't know for sure where the equations came from, but the ones we have apparently used here for a while that seem to work good on a variety of steel alloys are: (temperature in F)
Ac1 = 1333+40Si-25Mn-26Ni+42Cr
Ac3 = 1570-323C-25Nn+80Si-32Ni-3Cr
Ms = 1042-853C-60Mn-30Cr-30Ni-38Mo
Mf = Ms-483
Grampi1 in an earlier post provided a very interesting link that had some equations on a Nippon steel website as follows: (temperature in C)
Ac1=750.8-26.6C+17.6Si-11.6Mn-22.9Cu-23Ni+24.1Cr+22.5Mo-39.7V-5.7Ti+232.4Nb-169.4Al-894.7B
Ac3=937.2-436.5C+56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr+38.1Mo+124.8V+136.3Ti-19.1Nb+198.4Al+3315B
Ms=521-353C-22Si-24.3Mn-7.7Cu-17.3Ni-17.7Cr-25.8Mo
The two sets of equations get somewhat different results in some leaner low alloy steels, but not as significant differences for some higher alloy (but still low alloy) steels. The Nippon steel equations do not seem to work for Martinsitic stainless steels either.
So the question is, which equations are best for which types of alloys? Are there other equations that work better for a particular alloy family? Does anyone know where the first set of equations originated and what range of composition they were intended to be used for?
Ac1 = 1333+40Si-25Mn-26Ni+42Cr
Ac3 = 1570-323C-25Nn+80Si-32Ni-3Cr
Ms = 1042-853C-60Mn-30Cr-30Ni-38Mo
Mf = Ms-483
Grampi1 in an earlier post provided a very interesting link that had some equations on a Nippon steel website as follows: (temperature in C)
Ac1=750.8-26.6C+17.6Si-11.6Mn-22.9Cu-23Ni+24.1Cr+22.5Mo-39.7V-5.7Ti+232.4Nb-169.4Al-894.7B
Ac3=937.2-436.5C+56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr+38.1Mo+124.8V+136.3Ti-19.1Nb+198.4Al+3315B
Ms=521-353C-22Si-24.3Mn-7.7Cu-17.3Ni-17.7Cr-25.8Mo
The two sets of equations get somewhat different results in some leaner low alloy steels, but not as significant differences for some higher alloy (but still low alloy) steels. The Nippon steel equations do not seem to work for Martinsitic stainless steels either.
So the question is, which equations are best for which types of alloys? Are there other equations that work better for a particular alloy family? Does anyone know where the first set of equations originated and what range of composition they were intended to be used for?





RE: Calculating transition temperatures
I am new in this area and I read your Thread but I am not sure what's the transition temperature? Is it the melting temp and pouring temp. I am trying to find way to calculate the melting of any base alloy with different or variable elements. Is there such a formula that you can use to do so? Thank you for your reply.
Sonny Tran
RE: Calculating transition temperatures
No, not melting/pouring, but the temps. where various phases of steel change during heating and cooling.
The equations are interesting, but I can't add to them per the orig. request.
RE: Calculating transition temperatures
Ac1: the temperature at which austenite begins to form during heating.
Ac3: The temperature at which transformation of ferrite to austenite is completed during heating.
In both cases the letter c is due to the french word chauffage.
Ms: temperature at which austenite begins to transform during cooling.
There are many equations from different authors and with different scopes(of chemical compositions). All of them are obtained through numerical regression.The work of K.W. Andrews is old but still very intersting. It gives the equations for all these temperatures: K. W. Andrews,JISI, 1965, 203, (7), July, 721-727.
My best regards.
RE: Calculating transition temperatures
I think you may be trying something that is quite hard. much like the equations in this thread (and the carbon equivalence equations in a thread below), Empirical studies and regression analysis may be the only way .
for one or two alloying elements there are ways to calculate the phase diagram from thermodynamic properties such as enthalpy, entropy, heat of fusion, etc. As long as you know these properties, and can fit them to the proper calculus. (my thermo is a little rusty or Id be able to give some equations but I have done the above once.)(theres also some stuff you need to include with soulubility too....)
I think that with lots of different elements though trying to get an equation bsed on thermo theroy would be worthy of quite a prize.
nick
(GOOD LUCK)
Nick
I love materials science!
RE: Calculating transition temperatures
RE: Calculating transition temperatures
Thank you for all the information.
SDJVAR