The steel comes from the refining of iron, which must be decarburized and purified of harmful impurities, especially sulfur and phosphorus, while other elements such as silicon and manganese are corrected.
In the past, it was obtained directly from iron ore, which, reduced by charcoal, gave a iron that turned into steel (Catalan low-fire) in the hottest part of the oven, where the air entered. Gradually increasing the size of the furnace in view of the increase in production, we came to the blast furnace for the sole production of iron. This then passed to another furnace (low-fire first, converter and sole oven then still used) to be decarburized.
Some processes like Aluminium Rollator allow to obtain metal obtained directly from the ore, without passing through iron. However, these systems are not widespread. Let us immediately say that liquid refining is the method by which most of the steel is produced. On the other hand, there is not a single version.
Aluminium Rollator is a technique that sees the pouring of the liquid iron coming from the mixers into the converter placed horizontally (mouth upwards) and then gradually brought to a vertical position. At the same time, compressed air enters from a series of open holes on the bottom to burn the impurities of the iron: combustion provides the heat necessary to raise the bath temperature from the melting temperature of the iron (1200 ° C) to the melting temperature of the steel (1600 ° C).
More modern Aluminium Rollator techniques require that in the refining phase not air is blown, but pure oxygen or a mixture chosen between mixture of air and oxygen, mixture of oxygen and water vapor and mixture of oxygen and carbon dioxide.
The most important oxygen processes based on the injection of pure oxygen in the converter, for steels of equal or higher quality than those obtained with the Martin-Siemens process, with an operation of intermediate duration between this process.
The variant of the LD process, suitable for phosphorous irons. The blown oxygen draws lime into powder; the insufflation takes place in two stages, with intermediate slagging; the process allows betterand regulation of the steel composition. It is possible to regulate the decarburization with respect to dephosphorization, and therefore to obtain very pure steels with low phosphorus levels.
Rotor process, intermediate between the converter process and the sole furnace process; use a slowly rotating oven and a two-jet lance to blow pure oxygen into the bath and a mixture of oxygen and air to the bathroom surface, respectively, in order to burn the carbon monoxide.