Secondary metallurgy

Since the early 1960s, the increasingly stringent demands placed by users on steels in terms of chemical composition, physical cleanliness and processing characteristics have led to the development of a large number of increasingly complex metallurgical treatments that could not be carried out in the traditional steelworks reactor (oxygen converter or electric furnace). Operations carried out outside the furnace gave rise to a new type of metallurgy, known as "secondary" metallurgy, carried out in a steel mill ladle fitted with a range of equipment, including drawer nozzles and porous plugs.

Three aspects need to be considered to understand why secondary metallurgy emerged and developed.

• Productivity

  Clearly, it allows better utilization of the steelmaking equipment, in particular the high-capacity converters (350 t) and the electric furnace, by deferring the often time-consuming fine metallurgy operations to the ladle.

• Quality

  This is obviously the most important aspect. Out-of-furnace metallurgy improves :

  • The ladle metallurgy stage is increasingly becoming the essential link between the converter or electric furnace and the casting machine;

  • control of composition and very low levels of residual elements: C, H, N, O, P, S... ;

  • the inclusional cleanliness and morphology of the remaining inclusions; it also makes it possible to produce new steel grades that are difficult to obtain in a single operation.

• Lower costs

  This is a consequence of the previous two points. It's not always easy to estimate, since the cost of the new operation has to be taken into account, but the balance is generally largely positive.

  Throughout the text, underlined symbols such as $\underset{\_}{O}$ or [O] refer to elements dissolved in the metal, while slag constituents are shown in brackets (SiO ₂ ).