2019 Volume 91 Issue 2 Pages 87-93
Generally carbon equivalent is calculated with the following equation CE = [%C] + (1/3) [%Si]. However, the value calculated with chemical analysis methods such as Optical Emission Spectroscope is different from that calculated with the primary crystal temperature (Hereafter TL) of the CE meter. In this study, the influence of elements on primary crystal temperature and carbon equivalent in cast iron was examined, and a more accurate equation for calculating carbon equivalent is suggested.
The relationship between TL and elements from hypo-eutectic to eutectic composition is as follows ; TL (℃) = 1625－110[%C]－25[%Si] + 3[%Mn]－35[%P]－71[%S]－2[%Ni]－7[%Cr] Dividing this equation with carbon coefficient, a carbon equivalent equation from hypo to eutectic composition is obtained as follow ; CEL = [%C] + 0.23[%Si]－0.03[%Mn] + 0.32[%P] + 0.64[%S] + 0.02[%Ni] + 0.06[%Cr]. This is calculated from the drop in the solidification temperature and is different from the generally used CE = [%C] + (1/3) [%Si]. We investigated which causes the difference and which is more correct from hypo to eutectic composition.
From the review of references, it is sassumed that = [%C] + (1/3) [%Si] is calculated from the carbon solubility in hyper eutectic composition. Compared to this, as for the references in which carbon equivalent are calculated from the solidification temperature. from hypo to eutectic composition, Si coefficient is not (1/3) but 0.22 to 0.25.
From all the following viewpoints, it can be said that CEL = [%C] + 0.23[%Si] is more correct than CE = [%C] + (1/3) [%Si] : (a) experimental result, (b) cooling curve of CE meter, (c) carbon floatation result, (d) TL and chemical analysis, (e) internal shrinkage test result, and (f) thermodynamic simulation with JMatPro. The silicon coefficient (α) is constant at 0.23 until 3.65% silicon, but it increases linearly if the silicon content exceeds 3.65%.
