step 1 Scrap cleaning
At the entrance to the steelworks, scrap - the main raw material - is transported to the scrap yard. Measuring devices are installed at the entrance of the site to detect any radioactive source. About 15% comes from internal recycling and the rest is bought from stockists or scrap metal dealers from various sources:
-off-cuts from processing industries, including the automotive industry;
-used consumer goods (scrap cars, household appliances, cans);
-steel from the demolition of buildings;
The quality of scrap is key for the quality of the steel produced. All deliveries are controlled to isolate items that may affect the features of manufactured products, such as steriles (non-iron containing material). The less noble scrap is then cleaned by magnetic sorting to reduce emissions during melting and the energy consumption of the electric furnace.
Different categories of scrap are then mixed to meet the quality features required by customers and to ensure an optimal melting process.
step 2 Electric Arc Furnace
The scrap baskets arrive in the electric furnace, where the teams manage the injections and mix necessary for the fusion. The latter is thus achieved using the radiation energy of an electric arc, together with the heat of combustion of natural gas burners and the addition of anthracite.
The electric arc is produced by the passage of a continuous current of more than 135,000 amperes between the electrode, the scrap and the bottom of the furnace tank. The temperature inside the furnace then exceeds 1600⁰C, allowing the melting of the steel.
The steel is refined by oxygen insufflation, and the lime is used to form a slag to capture impurities contained in scrap, which form oxides under the action of oxygen, and bind to lime. The coal injection makes this slag foaming, which protects the upper vat from the radiation of the electric arc and improves the energy transfer to the steel bath.
The filters catching the furnace fumes, supplemented by a quenching and activated carbon injection system, meet the most stringent environmental standards.
When the load is completely melted, the furnace is drained. The steel is then poured into a ladle and transported to the ladle furnace.
step 3 Ladle furnace
In the ladle furnace, the steel is "shaded" – e.g. refined - through the addition of alloys that will achieve the mechanical properties required by the customers.
Homogenization of the steel bath is achieved by stirring with argon, an inert gas that does not react, even at high temperatures. In parallel, the desulfurization is carried out.
Throughout the process, the steel ladle is kept at temperature by the passage of a three-phase alternating current between the steel and three electrodes, introduced directly into the steel bath.
When the chemical analysis and the ideal temperature are reached, the steel ladle is ready for the continuous casting.
step 4 Continuous casting
Pulled up to the turnstile of the continuous casting and turned in casting position, the steel ladle is drained into the distributor serving both as a steel distributor -6 strands- and as a buffer tank when changing the ladle.
Under the distributor, the steel is poured into the copper mold and begins to solidify in contact with the mold which is cooled with water. Out of the mold, the thickness of the skin reaches about ten millimeters. The strand thus formed is guided by the segments and its cooling is continued via nozzles. Straightening extractors then pull it out of the installation, at a temperature still higher than 1000⁰C. Out of the extractors, the steel is solidified and can be cut. The automatic oxy-cutting gives the strand the length ordered by the rolling mills, giving rise to the semi-product, also called "beam-blank" or "dog bone".
step 5 The reheating furnace
Each rolling mill includes a reheating furnace, where hot or cold semi-products are pull into. The rolling process must indeed be carried out on hot products to manage quality and productivity. The steel, brought to a certain temperature, is transformed efficiently by limiting the number of passes and avoiding the breaking of rolling rolls in order to refine its grain and reach the mechanical properties required by the customers.
step 6 The rolling process
The rolling mill is an industrial installation that allows the reduction of thickness of the steel as well as a deformation of the product to obtain beams, angles or sheet piles. The rolling is operated at an average temperature of 1000 °. It produces an elongation of the product up to a hundred meters.
step 7 The finishing process
After cooling, the product is straightened and cut into commercial lengths, then prepared before shipment to the customer or intermediate users.