Production of Steel

1.       The Production of Steel

The production of steel is indeed a complex process which if not handled carefully can lead to accidents and the failure of receiving a good end product. The process of manufacturing steel is a long and tedious one that undergoes various procedures in order for the end product to transform into a fine and quality driven output. Provided below are the various steps explained briefly, about the manufacture of steel and its by-products.

i.                    The Raw Materials and the Coke Oven The raw materials used for the manufacture of steel are Iron Ore Pellets (i.e. small pebbles of raw Iron Deposits), Coal and Limestone (and Dolime in many cases). The coal is then converted to coke (tiny particles of coal) in the coke ovens. The impurities removed from refining the coal are usually sold in the market place as by-products. The newly refined coal is called ‘metallurgical coke’ or pure carbon. This metallurgical coke is used in the blast furnace while the limestone reserves are used to remove impurities.

  The Production of Steel

ii.                  Blast Furnace

This is considered a very essential part of steelmaking. The use of blast furnaces has been around for centuries.

Due to the drastic advancement in technology, the process of manufacturing steel has changed into a more sophisticated one. Many companies have different methods and techniques of manufacturing steel. After the iron ore is converted into molten metal by the Blast Furnace the output then undergoes a process called the “Basic Oxygen Furnace”. The basic oxygen furnace is a 300 tonnes oxygen converter. “70% iron and 30% recycled steel are mixed with other alloys in the 300-ton basic oxygen steelmaking furnace to create the metallurgical qualities which suit the customer’s end requirements” (METSOC, 2011). After the molten metal is converted into molten steel by the basic oxygen furnace it is then sent to the Steel Refining Facility.

iii.                Steel Refining Facility

The molten steel is sent in to the steel refining facility where the molten steel is refined into a fine and pure form of steel. This newly reformed and pure state of steel is then sent to the continuous casting plant to be converted into slabs of steel.

iv.                 Continuous Casting

The refined molten steel is poured into a casting machine to be converted into solid slabs of steel.

2.       A Brief study on the production of Steel in ArcelorMittal S.A.

ArcelorMittal is the largest manufacturers of steel in the world with 10% of the worlds steel production being produced by them (Fortune Global 500, 2010). Provided below is a brief study on the production of stainless steel in ArcelorMittal’s plant located in Paris, France.

a.       Stage 1 – The Melt Shop

The use of raw materials, mostly recycled stainless steel and ferro-alloys is converted into molten metal using an electric arc furnace with a melting capacity of up to 160 tonnes. The molten is then transferred to a converter. Alloying elements are added into the converted to obtain the chemical composition thus allowing the production of standard grades.

The ladle metallurgy consists of the addition of some alloying elements in order to obtain the similar chemical composition and the correct temperature before the continuous casting process. The produced molten steel is then poured, cooled and then solidified when undergoing the continuous casting process. During this stage, the maximum width of the steel is determined. The solid steel I cut with an oxygen flame into steel slabs that are up to 30 tonnes in weight, up to 12 metres in length, 200 mm thick and up to 2 metres wide. Some of the steel slabs are then ground in order to remove surface defects before being shipped to the hot rolling mill.

b.      Stage 2 – Hot Rolling Mill

This process takes place in the ArcelorMittal Chatelet and involves the reheating of the steel slabs in a furnace at a temperature of 1250 °C.  The first reduction of the steel slabs with regards to thickness is from 200 mm to 40 mm after several passes on the roughing mill. The thermal tunnel is responsible for maintaining the temperature of the steel slabs that are reduced in thickness.

The slab then is passed through a series of 7 rolling stands to reach a reduced size of approximately 3 mm in thickness. The metal is then cooled and wound to form coils or also known as “black coils” due to their oxidized nature and then shipped to ArcelorMittal’s annealing and pickling plant. ArcelorMittal also sells black coil to customers upon request.

Fig 2.1 Conversion of Steel Slabs into Black Coils

c.       Stage 3 – Annealing and Pickling

The Black coils are then heated in the annealing furnace. This step allows the recovery of the stainless steel. The oxides of the surface of the steel are broken down by shot blasting.

The pickling process in the acid baths followed by water cleaning and air drying results in the transformation of the black coils into white coils with no surface oxide; this is called the HRAP finish. At this stage, the white coils or HRAP coils can be sold in the market without cold rolling or further surface finishing.

d.      Stage 4 – Cold Rolling and Final Annealing

This stage allows the reduction of the thickness of the HRAP coil strips down to minimum of 0.3 mm to meet the customer’s final requirements for stainless steel. A final annealing provides the required properties for the use of the customer. The cold rolling process helps produce the flatness of the stainless steel together with an enhanced surface finish suitable for household appliances (e.g. Stainless-steel cutleries).

e.      Stage 5 – Metal Finishing

The end product is then slit to width and cut in to length also allowing for some specific surface finishes to be made. These metal finishing operations are carried out in ArcelorMittals’s production plants and through their network of service centres. The end products, according to ArcelorMittal, are 100% recyclable at the end of their life.

 3.       Reference(s)

METSOC. (2011). Steel Production Flow-Sheet. Available: http://www.metsoc.org/virtualtour/processes/steel.asp. Last accessed 11th February, 2012

Cable News Network (CNN). (2010). Fortune Global 500 2010: The World's Biggest Companies - ArcelorMittal - MT. Available: http://money.cnn.com/magazines/fortune/global500/2010/snapshots/11208.html. Last accessed 10th February, 2012.

ArcelorMittal . (2009). What is Stainless Steel? Manufacturing Process. ArcelorMittal Paris Stainless Europe. 1 (1-5), p1-5.