2026 Regordosa Cast Iron Shrinkage Defect

Standard thermal analysis cups can be seen as small riser-less sand castings prone to show shrinkage defect. This characteristic was used to compare the shrinkage tendency of two slightly hypoeutectic spheroidal graphite irons, a standard one with about 2.4 wt.% Si and a high-silicon one with about 3.9 wt.% Si. The other process variables that were investigated were the pouring temperature and the inoculation level. After casting, the samples were quantitatively characterized by X-ray tomography that showed internal shrinkage defect as well as outward and inward sinking of the outer surfaces. While the internal shrinkage defect increased from low-silicon to high-silicon alloy for low pouring temperature, the reverse was observed for high pouring temperature. Also, all of the cast samples showed inward sinking of the flat surfaces of the thermal analysis cups, which was minimum for non-inoculated samples, and in general, higher for inoculated high-silicon alloy than for the inoculated low-silicon alloy. Crossed analysis of shrinkage defect and the changes in the outer shape of the cast samples is then discussed in terms of solidification at the scale of the cups that is based on dedicated thermal records. It is suggested that internal shrinkage and inward sinking are closely related through the mechanical behavior of the outer part of the cups that is solid or mechanically coherent while the central part still behaves as a slurry.