Prediction of Graphite Nodule Count and Shrinkage Tendency in Ductile Cast Iron, with 1 Cup Thermal Analysis

Abstract

Although 3 cup thermal analysis is a good method to predict the molten metal’s quality in gray cast iron, it could not be used in ductile cast iron due to several reasons. We have succeeded in investigating the graphite eutectic temperature (hereafter simply shown as TEG) and cementite eutectic temperature (hereafter simply shown as TEC) in ductile cast iron, from the chemical composition of the molten metal, as follows: $$ {\text{TEG}} = 1149.1\left( {^\circ {\text{C}}} \right) + 4.7{\text{Si mass\% }} - 4.0\left[ {{\text{Sol}}.{\text{Mn mass\% }}} \right] - 44{\text{P mass\% etc}}. $$ $$ {\text{TEC}} = 1142.6\left( {^\circ {\text{C}}} \right) - 11.6{\text{Si mass\% }} - 0.75\left[ {{\text{Sol}}.{\text{Mn mass\% }}} \right] - 46.2{\text{P mass\% etc}}. $$ (hereafter, mass% is simply shown as %). We added various kinds of inoculants into the molten metals and then cast them at various fading time into 1 cup. Using the cooling curve of 1 cup and above equations, we calculated eutectic graphitization ability (hereafter simply shown as EGA). The graphite nodule count (N) of CE cup T.P. is determined by $$ {\text{EGA}}\left( { = 100 \times {\text{DT}}1/{\text{DTE}}} \right) $$ as follows: $$ N = 6.13 \times \left( {100 \times {\text{DT}}1/{\text{DTE}}} \right) - 126 $$ . In addition, when EGA becomes over 70 %, shrinkage tendency (θ) becomes low near 60°. Consequently, 1 cup thermal analysis is a good system to predict graphite nodule count and shrinkage tendency (θ) correctly in ductile cast iron, before pouring it.