Cast steel is a type of metal created by heating iron using a crucible container. Its creation was due to a revolutionary process invented by an Englishman, Benjamin Huntsman, the 1751. Cast steel allowed for a more uniform composition of, and fewer impurities in, steel than any previous manufacturing process. Since it is made in a crucible, cast steel is often called crucible steel.
Steel is made by combining iron with carbon or other alloys. Iron is a soft metal, so not ideal for many construction purposes. The creation of steel removes many of the impurities in iron, which allows steel to be harder and more durable. The better the steel, the more iron impurities that are removed.
Early steel was made by adding small amounts of carbon to iron. For example, blister steel was made by repeatedly heating wrought iron and charcoal together in a kiln. The charcoal's carbon transfered to the steel by the process of diffusion.
Cast steel was the first type of steel that allowed alloys to be added to the iron. Prior to this method, manufacturers had not been able to get steel hot enough to melt. By heating blister steel in a clay crucible placed directly into a fire, Huntsman allowed the metal to reach up to 2900°F (1600°C). Melting allowed other elements, such as nickel, to be mixed into the metal, thus strengthening the steel.
Over the centuries, improvements in the crucible process have been made, though the steel is still heated by fire and inside a clay, pot-shaped crucible that can be sealed. Modern cast steel is use in engines and machines, as well as ship building. It tends to be more expensive than other types of metals used for similar projects.
Cast steel has a rough finish. It often has surface holes created by gas bubbling during the heating process. An elastic metal, this type of steel is very tough, having four times the tensile strength of cast iron. Tensile strength is how much pressure, created by pulling, an object can withstand before it breaks.
One concern when using cast steel is whether the surface holes extend into the interior of the metal. If so, these holes could create weaknesses that affect the soundness of the steel. Measuring the volume of water that can be poured into the holes will give a good indication of whether the holes extend far into the metal.