Influence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot was analyzed by using finite element method. The results of analysis were compared with those of sectioning investigation of 100t and 135t ingots, and the influence of mould and hot top design on the internal defects has been made clear quantitatively.
The result shows that the geometry of hot top and mould design plays most important role on the manufacture of sound heavy ingots. The central porosities and loose structure are liable to increase when the rate of vertical solidification at the centerline of ingot exceeds the value of about 10mm/min., and the defects are strengthened at the area where the rate of solidification is accelerated.
For 0.25%C-3.5%Ni-Cr-Mo-V steel ingot, "A" segregation begins to form when the rate of transverse (horizontal) solidification decreases to the value of about 0.8mm/min.