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 T_L) 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 T_L and elements from hypo-eutectic to eutectic composition is as follows ; T_L (℃) = 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 ; CE_L = [%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 CE_L = [%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) T_L 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%.

  In the hot strip mill of the steel manufacturing process, the run-out table roller transports the steel sheet and coil at high speed between the finishing rolling mills and down coiler machines. For this reason, the roller is required to withstand contact with the rolled product in high temperature in a water-cooled environment. Fe-Cr-V-C alloyed cast steels were developed and systematic investigation of material properties and functions was carried out. The metallurgical structure consisted of M₇C₃ carbide, dispersed granular MC carbide and matrix. This material has superior corrosion resistance, abrasion resistance, thermal crack resistance and seizure resistance. Cr forms M₇C₃ type carbide and V forms MC type carbide with high-hardness respectively, and they are partially dissolved in the matrix. The amount of carbide is increased with the increase in C, Cr and V contents of the carbide forming element to improve wear resistance. Corrosion resistance improves with increasing (Cr + Ni + Mo) / C value. Using this material as a shell material combined with the steel inner base material, a composite sleeve was made by the continuous pouring process for cladding, and this composite sleeve was used for the actual rolling operation. As a result, improvement of the durability of this roll was confirmed.