Steel-works

A steel-works is a Usine being used to produce Acier in great quantities, generally in the shape of semi-finished products. One generally distinguishes 2 types of steel-works: the electric steel-workses which produce steel starting from recycled scrap, and the steel-works with oxygen which work starting from cast iron liquid produced by a Haut-fourneau

Tools

desulphurization (To remove the sulfur of the cast iron from the blast furnaces)
cast iron pockets (Charging in the converter)
the troughs (Charging of scrap in the converter)
the cleansing of the cast iron (To remove the filth after desulphurization)
converters with oxygen (Transformation of the cast iron into steel)
the pockets steel (the container of steel for the metallurgy out of pocket and casting in continuous casting)
rocking-levers of pocket (preparation of the pocket steel for casting in continuous casting)
metallurgy out of pocket (Put at nuance refining of steel)
continuous casting (solidification of metal by cooling with water)
the overhead travelling cranes (essential for transport of the pockets)

Reception matters

The principal products used by steel-works are:

cast iron, if it is about one oxygen steel plant
scrap
oxygen
lime
the alloy elements
the refractory materials

Pretreatment of the cast iron (oxygen steel plant only)

One generally finds there:

workshop of desulphurization. While injecting calcium carbide and magnesium, sulfur will form oxides which will float towards the dairy of the cast iron. This slag will then be removed using a scraper. Other desulphurizing agents, as soda, can be also used.
the station of mixture. By mixing pig iron and cast iron castings, it is possible to optimize the temperature or the composition of the cast iron used converter.

It should be noted that desulphurization is sometimes regarded as a workshop depend on the blast furnaces

Converter

See also converter and Manufacture of steel

Oxygen converter

See Manufacture of steel

Electric furnace

Appeared in the Sixties, the production of steel starting from bought scrap melted in an electric furnace at summer posed like a technico-economic model by Nucor Corporation with the the United States. A basket covered with bricks Réfractaire S is filled of scrap, which is remelted using a powerful electric arc. The arc is generated by 3 electrodes in Graphite supplied with alternative course, or sometimes by only one electrode functioning in D.C. current.

Advantages

the raw material, made up of scrap generally recovered with the magnet, is competitive with respect to the ore and of coke.
This die does not need Haut-fourneau and the enormous mobilization of capital which he claims regularly (a repair of refractories every 15 years, costing more than 100 million euros and lasting 3 months).
an electric furnace is much more flexible and robust that a Haut-fourneau

Inconvénients

It is difficult to control the quality of scrap, in particular lived pollution in Cuivre (weakening element, coming from the not located electrical motors). This ultimate stress generally the electric die with the manufacture of long products and the conveniences.
the price of scrap is also very fluctuating
the " gisement" on scrap depends on the level development and equipment of the vicinity. Even in Europe, it is difficult to find more than one million tons of scrap per annum.

Metallurgy out of pocket

The metallurgy of molten steel appeared when one knew to eliminate the Phosphore present in the iron ore, by the blowing of steel in the presence of Chaux in the basic Bessemer converters

The metallurgy out of pocket appeared when the alloys to be worked out became too complex to be carried out in only one engine, the converter. Currently, the liquid steelmaking is completed after it was cast converter (or electric furnace) in the pocket. The objective is then of:

to drive out the last chemical elements resulting from the cast iron (carbon, phosphorus and sulfur).
to consume gases dissolves in molten steel (Oxygène of the converter, Hydrogène of scrap, Azote).
to eliminate inclusion from Oxide S floating in metal.
to reach, at the best cost, the chemical composition concerned.
to reach the temperature of casting requested by the tool downstream, casting.

Treatment of the slag

It was seen that the dairy can remove the Soufre cast iron. The converter, a slag rich in Chaux also makes it possible to remove the Phosphore. In these cases, the slag is isolated from the surface of the bath once the molten chemical reaction metal - slag finished.

The dairy can also absorb dissolved inclusions of Oxyde S in metal, generally resulting from steel-killing. For that, it is essential to control its composition, so as to make it reactive. A high content of Chaux, for example, returns the slag Basique what is favorable with respect to alumina inclusions. However, this slag must also spare the bricks Réfractaire S… the adjustment of the slags is thus a compromise.

Some Oxide S of the slag, like FeO, can oxidize the additions of alloy like the Titane, the Aluminum, the Bore,… In this case, these alloy elements are consumed, therefore wasted, before reaching the molten metal. A quantity of dairy too important, or a Oxydation of the dairy badly controlled is thus in this crippling case.

The tools related to the treatment of the dairy generally consist of a " rateau" for " écrémer" the dairy floating on molten steel. Hoppers allow the addition of the intended products to constitute or amend the dairy .

Tools of passage to the vacuum

Two tools are generally used to pass the Acier vacuum liquid (value being able to be lower than 1 mbar):

the Vacuum Out of Tank. The pocket is descended in a tank. A lid comes to be put above to close the tight enclosure of way. The vacuum is obtained using vacuum pumps and ejector S assembled in series. Being given the density of the molten metal, the effect of the vacuum appears only on the surface of the bath. Metal thus should be brewed, using porous stoppers assembled at the bottom of the pocket, which blow of the Argon.
RH

Station of mixing and setting with nuance

The setting with nuance (addition of the elements of Alloy) can be done with the Convertisseur, once the cycle of decarburization completed. Being given the diversity of the nuances of Steel to be produced and the constraints related to the dissolution of the alloy elements, this practice tends to disappear. Generally, the setting with nuance of the Acier liquid is done with specific tools, in several stages:

Addition of the alloy elements chemically " robustes". Typically, one can add iron-manganese-carbon (a cast iron of Manganèse), which will be decarbonized partially in contact with the Oxygène dissolves in molten steel. The Manganèse is generally the first alloy element in term of quantity: its addition as soon as possible is thus a means of also ensuring its dissolution.
Steel-killing . It is about the addition of elements having a strong affinity with oxygen dissolves in the bath, typically the Aluminum for the flat products, and the Silicium for the long products. These elements, while removing steel from sound Oxygen, will create oxides which will float towards the dairy .
Addition of the elements of Alloy. Once steel calmed , one can proceed to the addition of the invaluable additions such as the Vanadium, the Niobium, the Titane,… The absorption of oxygen at the time of the operation of steel-killing avoids the oxidation of these elements: the losses thus are limited. The addition of these elements can be done by gravity starting from hoppers: in this case, the alloy elements will have to cross the dairy before reaching steel. One must then control the composition of this layer, or locally discover well the bath while working under a neutral atmosphere of Argon (proceeded CASE). It is also possible to inject directly into the molten metal, with immersed lances, these finely crushed alloy elements. The transport of the alloy elements inside the lance is done with argon. A third possibility consists in injecting a long steel pipe, fills of alloy elements in the form of powder. This solution allows an excellent protection of the added elements, but does not allow the addition of large quantities.

The order above is generally respected. One must however know that steel-killing is really necessary only if steel will be solidified using a continuous casting . The run in ingot allows steel the solidification rimming, the rimmed steel , free from impurities, because the Oxyde S created by steel-killing do not float all worms the dairy . Moreover, solidification induces the degasification of the Oxygène dissolves which, while going up towards surface, cleans and brews still liquid steel.

The passage by a tool of vacuum is also possible. If the role of this tool is to perfect the decarburization started with the Convertisseur, this stage will have to be done before steel-killing. If the objective is the desydrogenation or the denitridation , this stage will come once the final chemical composition reached.

The mixing is made as soon as one adds the elements of Alliage. It can be pneumatic: Argon is then injected with an immersed lance, or through refractory bricks papering the pocket. Mixing can also be electromagnetic.

The role of the dairy should never be neglected at the time of the phase of addition of the alloy elements. Indeed, it can disturb the operation in:

régurgitant undesirable elements, like the Phosphorus or the Sulfur: the additions and steel-killing indeed will modify chemical balance between molten steel and the dairy .
oxidizing the elements of addition. In addition to the associated costs with the consumption of part of these elements, the fraction oxidized by a nonreduced slag (for example, rich in FeO) cannot be predicted. It then becomes difficult to reach the chemical composition concerned.

Setting at temperature

Continuous casting request typically temperature of Acier of approximately 30°C to the top of the Liquidus of the Alliage. The means of reheating are, either the electric furnace with pockets, or a chemical process like the Aluminothermie. It is also possible to work all the time very hot, to cool at the good temperature only at the last time.

Run

Continuous casting

Continuous casting is the tool for solidification of metal. The pocket steel is posed on a pivotor, who have two arms, to accommodate two pockets, and of this fact of running uninterrupted. Metal runs out via the channel of cast in a distributer which will distribute it on two lines of casting. At exit of the distributer, metal arrives in the ingot mould which will give him its final form (slab) by water cooling. At the end of the line, the slab is cut to the length desired by oxycutting (a large blowtorch). Next stage, rolling.

Run in ingot

Casting in ingot is the ancestor of continuous casting, and is not used practically any more.

History

August 1st The development of the steel-works follows a way parallel with the Industrial revolution. Indeed, the industrial production required solid tools at reasonable price. The work of the iron ore, available almost everywhere, became more and more adapted to the mass production, while the quality of the Acier S did not cease improving.

See History of the production of steel

External bond

of the steel-works

Bond towards the site of SteelUniversity.org

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