I’m familiar with the use of rollers to make glass panes but surely it’s not that?
In: Engineering
Most solid metals are poly crystalline; if you cut, polish and etch them and put them under a microscope you will see they are made up of many single crystals packed together called grains. Glass has no such crystals and is called amorphous.
In cast steel, molten metal is poured into a mold, and as the liquid metal cools, grains are formed according to how heat is extracted from the mold ie as temperature drops liquid changes to solid. Grains crystallise from the contact area of the mold to its interior metal in arrangements called dendrites or columns, depending on the speed of heat loss. If very slow, they are planar.
In rolled steel, hot solid metal is squeezed through rollers and the grains are elongated and stretched against each other in a single direction, which strengthens the steel plate on the surface where it is being rolled.
Comparing the surfaces of the cast and rolled steel, the grains are arranged more strongly in rolled metal than cast metal to compressive and tensile forces, which makes it better for resisting projectiles.
Steel has to be rolled at the correct temperature so the desirable grain shapes are maintained and no new grains are formed(recrystalisation), and just like rolling glass then is a limit to how much it can be deformed in one go, or it will crack.
It has to be hot enough to be worked and formed, but not so hot that the elongated grains shrink and form new compact grain shapes.
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