由于钢锭结晶时从表面向中央推进,金属从液体变为固体时体积的缩小,以及在此转变时气体含量的减少等情况,因此在钢锭的中心一定产生缩孔。缩孔在钢锭上部形成,也就是说在最后凝固的地方形成。但缩孔可能分成两个(即二次缩孔)或两个以上的部分,这要视钢锭的冷却条件而异,在缩孔下面经常有疏松,它的形成原因是与缩孔相同的。在缩孔附近 As the ingot crystallizes from the surface to the center, shrinkage of the metal from liquid to solid, and reduction of the gas content during the transition, shrinkage is sure to occur in the center of the ingot. Shrinkage cavities in the upper part of the formation, that is to say the final solidification of the place. However, shrinkage may be divided into two (ie, secondary shrinkage) or more than two parts, depending on the ingot cooling conditions vary often below the shrinkage porosity loose, it is formed because of the same shrinkage. Near the shrinkage hole