Ac1 temperature calculation

[firkelloy]

Does anyone have an equation to calculate the Ac1/Ac3 temperature for steel from its chemistry? I am more interested in the Ac1. Any information you have would be helpful.

Thank you.

 

[vivekSS]

i am also looking for the same. in case u get a lead kindly pass it on.
regs,
vivek

 

[firkelloy]

This information comes from G. Krauss in Steels: Heat Treatment and Processing Principles (an excellent book). Krauss got the equations from KW Andrews, Empirical Formaulae for the Calculation of Some Transformation Temperatures, JISI, Vol 203, 1965, p721-727:

Ac3=910 - 203(C)^.5 - 15.2Ni + 44.7Si + 104V + 31.5Mo + 13.1W

Ac1=723 - 10.7Mn - 16.9Ni + 29.1Si + 16.9Cr + 290As + 6.38W

This gives you the temperature in deg C, when you enter in the weight percent of the element. I found that these equations work well for most alloys. When you get into large amounts of chromium (>> 1 wt%), they fail, giving an Ac3<Ac1.

Enjoy!