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Industrial process

Pickling

Packaging steels are made using low-carbon steel (0.03 to 0.13%).
The hot-rolled coils are welded together to form a continuous strip. The steel is then pickled to eliminate the iron oxide that forms on the strip during hot rolling and to prepare the strip for the cold-rolling mill.

The pickling process involves two successive actions :

•  the first is mechanical : descaling
•  the second is chemical : the steel is immersed into a bath of sulfuric or hydrochloric acid.


Rolling

Strip steel is cold-rolled in order to reduce its thickness. The steel strip is rolled in a tandem or reverse rolling mill which flattens and stretches the strip to the required thickness. The process can reduce the thickness of the strip by up to ten times without modifying the width. The resultant strip is approximately ten times longer.

The drawback of this process is that internal tension is created, making the strip less supple and more brittle.


Degreasing

After cold rolling, the steel is covered with a thin film of oil, which needs to be removed in order to optimize the annealing process.

Degreasing involves both :

•  a mechanical action : brushing of both sides of the strip
•  and a chemical action : immersion in degreasing baths heated to 96°C.


Annealing

This is a heat treatment that restores the steel’s plasticity lost during the cold-rolling process. Annealing is the heating of steel to above the recrystallization point. The steel is heated in a reducing atmosphere (a mix of nitrogen and hydrogen) to avoid oxidation.

There are two annealing techniques :

•  batch annealing
•  and continuous annealing. In the latter, tight control of the speed of the strip during the heating and cooling phases ensures complete regeneration of the steel grain.


Tempering

After annealing, the strip is tempered in order to achieve the required level of hardness, the required surface, good evenness and the required mechanical properties.


Coating

Blackplate can be coated with tin or chrome on the coating line, to obtain tinplate or TFS (Tin Free Steel). The maximum speed of a tinplate coating line is about 450 m/mn, equivament to 25 000 cans/mn.

The coating protects the steel against oxidation and facilitates subsequent welding operations.


Shearing

The coils are cut into sheets according to the customer’s specifications. Littell shears are used to ensure high-precision straight or indented cuts.


Packing

ArcelorMittal serves customers throughout the world and uses both overland and maritime shipment methods.

The coils and sheet are prepared and packaged depending on the final destination and means of transportation.