Solidification — Macrostructures and product quality

Many characteristics of cast products are strongly influenced by the nature of the solidification process and by the operating conditions chosen for the same process.

To take the simplest example, shrinkage due to metal contraction during solidification, can lead to the rejection of 15-20% of steel cast in static molds, if the steel cast in this way is calmed, i.e. deoxidized 1.5.1 . In the same ingot mould, effervescent solidification of the same steel, which has not been deoxidized beforehand (solidification with CO gas release), can be carried out with great skill. Solidification shrinkage can then be compensated for by the appearance of blowholes evenly distributed throughout the ingot (small, closed, non-oxidized cavities whose walls are re-welded during hot rolling), so that metal scrap is reduced to just a few percent 1.5.2 . When solidifying quenched steel, it is also possible to reduce the extent of the zone affected by solidification shrinkage by providing a feeder, a reservoir of liquid metal which supplies metal to the zones undergoing solidification 1.5.1 . We can also speak of a feeder maintained during the manufacture of steel ingots by electrode remelting (electroslag remelting or vacuum remelting): the reservoir of liquid metal on top of the ingot being formed is renewed as it solidifies, thanks to the controlled melting of an electrode placed on top of the ingot. Continuous casting uses...