Question

What are “Rimmed” and “Killed” steels that an engineer should know? Explain them briefly.

Answer 1

Rimmed steel: Rimmed steels are low carbon steels that have less than .1% of carbon in them. Iron oxide or iron metal are place in furnace where it is reduced to remove impurities. Later is is passed through the refining furnace and then the metal is poured into cast iron ingot mold. As it solidifies, a layer of (nearly) pure iron is formed on the walls and bottom of the mold. Almost all the carbon, phosphorus, and sulfur moves to the central core. Carbon monoxide gas is formed because of oxygen and is trapped as blow holes in the solidifying metal.

Rimmed steel is malleable, they are used for manufacturing of sheets. Advantages of rimmed steel is defectfree and smooth surface on sheet products. Piping shrinkage can be avoided with use of rimmed steel. They are porus due to formation of carbon monoxide bubbles which is a disadvantage.

Killed steel: The word 'KILLED' implies that the steel is fully deoxidized before casting. Unlike rimmed steel, there is no evolution of gases in killed steel. As there are no voids, shrinkage pipe forms and amount of useful metal reduces. Killed steels are used for alloy steels, carburizing steel and forging steel. They have uniform composition and properties.