The oxygen combines with carbon and other unwanted elements and rapidly burns out impurities, converting the pig iron into steel. In some furnaces, electricity instead of fire supplies the heat. Because refining conditions in such a furnace can be strictly regulated, electric furnaces are particularly valuable for producing steels that must be made to exacting specifications. The process of making the tough, flexible alloy known as wrought iron differs markedly from other forms of steelmaking. Wrought iron is no longer produced commercially because it can be replaced in nearly all applications by low-carbon steel, which is less expensive to produce and is typically of more uniform quality than wrought iron.
Steel is marketed in a wide variety of sizes and shapes.
These are produced at steel mills by rolling and otherwise forming heated ingots to the required shape. In hot rolling the cast ingot is first heated to bright-red heat in a furnace and is then passed between a series of pairs of metal rollers that squeeze it to the desired size and shape. The distance between the rollers diminishes for each successive pair as the steel is elongated and reduced in thickness. Pipes are shaped by bending a flat strip of hot steel into cylindrical form and welding the edges or by piercing a solid rod of steel with a pointed metal bar that forms the inside diameter of the pipe. By far the most important coated product of the steel mill is plate for the manufacture of containers.