Unit 6
Production of liquid steel, Steel casting, Electric furnace
Pig iron treatment
The pig iron from the blast furnace is taken to the steel plant in
torpedo ladles. These are first of all desulphurised with calcium
carbide, which is introduced into the pig iron bath via an injection
lance. The calcium sulphide formed floats as a slag on the pig iron. The
torpedo ladle is then emptied into the pig iron ladle. This ladle is
taken to the slag removal station where the slag from the blast furnace
and the desulphurization process is removed.
Exercise 1:
Translate the following text into Czech:
Pig iron treatment
The pig iron from the blast furnace is taken to the steel plant in
torpedo ladles. These are first of all desulphurised with calcium
carbide, which is introduced into the pig iron bath via an injection
lance. The calcium sulphide formed floats as a slag on the pig iron. The
torpedo ladle is then emptied into the pig iron ladle. This ladle is
taken to the slag removal station where the slag from the blast furnace
and the desulphurization process is removed.
Answer Key: Exercise 1
After the slag removal, the pig iron is poured into the converter or BOF vessel. Scrap is added. Pure oxygen is blown through a lance onto the metal bath to burn off the excess carbon and impurities. At the same time silicon, manganese, phosphorus and residual sulphur present in the pig iron are also burnt off. To allow the purification process to proceed optimally, an amount of lime is added to the bath and an inert gas is blown through the bottom of the ladle. The reaction with oxygen during the blowing process produces heat. By the addition of scrap, the temperature of the bath is controlled at about 1560 ˚C after the blowing process. The pig iron becomes steel.
At the end of the blowing process in the converter, the composition of steel is always about the same. To obtain different steel grades, the chemical composition has to be adjusted. Additives and alloying elements are added to the converter to obtain the desired steel grade. The steel is poured in such a way that the converter slag is removed separately.
Exercise 2:
Exercise 3:
Use Internet for the following task:
Why is pig iron called pig iron and not "raw" iron (comparing to Czech “Surové železo“ and German “Roheisen”)?
Answer Key: Exercise 3
To obtain an even better steel quality, the steel ladle is taken to the ladle treatment station. Here the steel can be cooled by adding small bits of scrap, and alloying material can also be added. A stirring lance is introduced into the steel while an inert gas is blown through it. The ensuring agitation results in an improved homogeneity of temperature and steel composition. In addition, inclusions and impurities are brought to the surface so that the steel is optimally purified. By adding aluminum, the oxygen still present in the steel is bound: the steel has become aluminum-killed. This is necessary for continuous casting. The steel now has the required composition and temperature.
Special steel grades which require very low carbon content are treated in the vacuum degasser of the steel ladle treatment station. It is done by lowering two snorkels into the steel. The steel is then drawn up into the degassing vessel by vacuum. Owing to the low pressure, the oxygen is combined with the carbon in the steel. The resulting gas is drawn off. In this way, the carbon content of steel can be reduced to extremely low values.
Exercise 4:
Translate the following text into Czech:
To obtain an even better steel quality, the steel ladle is taken to the ladle treatment station. Here the steel can be cooled by adding small bits of scrap, and alloying material can also be added. A stirring lance is introduced into the steel while an inert gas is blown through it. The ensuring agitation results in an improved homogeneity of temperature and steel composition. In addition, inclusions and impurities are brought to the surface so that the steel is optimally purified.
Answer Key: Exercise 4
Exercise 5:
Iron -
Carbon monoxide -
Calcium -
Magnesium -
Calcium carbide -
Calcium sulphide -
Aluminum-killed -
Ammonia -
Benzene -
Tar -
Lime -
After the steel ladle treatment, the ladle is taken to the continuous casting unit. Liquid steel runs from the ladle into the pouring basin or tundish that divides the steel over the strand casters. A strand caster consists of a casting mould that is cooled by water and a series of rolls. Spray heads in between the rolls apply cooling water to ensure a further solidification of the steel. The casting mould determines the dimensions of the strand cast. To prevent the solidifying steel from sticking to the wall of the mould, the latter is continuously oscillating.
After the tap hole of the ladle has been opened, pouring continues until the ladle is empty. Because the tundish has a considerable buffer capacity, it is easy to exchange the empty ladle for a full one without interrupting casting into the mould. That is why the process is called continuous casting.
The strands emerge from the installation in a solidified state onto a horizontal roller table. Subsequently they are cut to length. Then the slabs thus obtained are slit lengthwise according to the widths that have been ordered.
Usually the slabs are cooled and inspected carefully for casting defects. Surface faults are removed by scarfing and the slabs are then transported to the reheating furnaces. Slabs with a perfect surface can also be introduced into these furnaces while still hot. This is called hot charging.
Exercise 6:
1. Simplified description of continuous casting:
In the continuous casting unit, steel from the ladle is poured into the tundish and then into the caster.
2. What does a caster consist of?
Caster consists of a casting mould that is cooled by water.
3. Why is it called continuous casting?
Because the tundish has a considerable buffer capacity, it is easy to exchange the empty ladle for a full one without interrupting casting into the mould. That is why the process is called continuous casting.
4. What product do we get from the casting process?
From casting, we obtain slabs.
When using an electric furnace, the sintering plant, the coking plant, the blast furnace and the converter are no longer required.
The raw material for an electric furnace is scrap metal. The scrap is charged into the furnace and melted by electrical energy. This energy is supplied by an electric arc between the furnace charge and large graphite electrodes. The liquid steel is poured into the steel ladle and acquires the required composition by the addition of alloying elements in the steel ladle treatment station.
Most electric furnaces have a capacity of about 150 tons. The reactions in the furnace are comparable with those in the converter in the blast furnace process. Unwanted elements can be removed by oxidation. However, not all elements are amenable to this method of removal, which means that the selection of the scrap to be used is of crucial importance, since some alloy elements present in the scrap metal will be retained in the liquid steel. With modern furnaces, the process takes less than one hour.
Exercise 7:
Exercise 2:
Exercise 7:
The raw material for an electric furnace is metal. The is into the furnace and melted by electrical energy. This energy is supplied by an electric between the furnace charge and large graphite electrodes. The liquid steel is poured into the steel and acquires the required composition by the addition of elements in the steel ladle treatment station.
Most furnaces have a capacity of about 150 tons. The reactions in the furnace are comparable with those in the converter in the furnace process. Unwanted elements can be removed by . However, not all elements are amenable to this method of removal, which means that the selection of the to be used is of crucial importance, since some alloy elements present in the metal will be retained in the liquid steel. With modern furnaces, the process takes less than one hour.
Points to remember:
- A better steel quality can be achieved in the ladle treatment station (e.g. vacuum degassing).
- Slabs emerging from the continuous casting machine are either
transported to the reheating furnaces while still hot (hot charge) or
stored for later cold charge (surface defects are removed by scarfing).
- When using an electric furnace, the sintering plant, the coking
plant, the blast furnace and the converter are no longer required.
Glossary:
| English | Czech |
| Caster | Lička |
| Continuous casting | Kontilití |
| Hot charge | Teplá vsázka |
| Mould | Licí forma |
| Scarfing | Čištění plamenem |
| Slab | Brama |
| Tundish | Nálevka |
| Vacuum degassing | Vakuové odsávání |
Gallery:
Ladle Treatment Stations
|
Continuous Casting
|
Continuous Casting
|
Continuous Casting
|
Electric Arc Furnace
|
Converter
|
Converter
|
Flux
|
Sources:
Applebaum, M, Everything You Always Wanted to Know About
Steel. A Glossary of Terms and Concepts, Summer 1998, Solomon Smith
Barney Inc., 2000,
Meseure, K., Steel Making, ArcelorMittal R&D Gent, ArcelorMittal University - Understanding Steel, 2009
Meseure, K., Steel properties, ArcelorMittal R&D Gent, ArcelorMittal University - Understanding Steel, 2008
An Introduction to the Hot Strip Mill, John Lysaght (Australia) Limited, 1976
PC Translator. CD-ROM. Korytná:LangSoft & SOFTEX Software, 2007
http://www.myarcelormittal.com
http://www.onesteel.com/
http://www.pdmsteel.com/index.html
http://www.steel.org/
http://www.steel-training.co.uk
http://www.stemcor.com/default.aspx
http://www.uss.com/corp/index.asp