blowhole

A blowhole in metal is a void caused by trapped gas bubbles during solidification. This can occur when steel is cast into an ingot, which is a mass of metal shaped for easier handling and further processing.12

Steel ingots vary greatly in size, from small blocks to massive, tapered shapes weighing over 500 tons. During the casting process, as liquid steel cools and solidifies, it shrinks. This shrinkage can create a cavity at the top of the ingot. To minimize this, methods like using insulating refractory heads or adding exothermic powders are employed. Some steels, known as rimmed steels, are cast with controlled gas evolution to create a cleaner shell and avoid an open cavity, though they may contain internal blowholes that typically weld shut during hot rolling.23