The following are the five ways steel mills brought their raw materials:
1. Limestone: Limestone is used as a slag former in the iron and steel making process. The slag has several functions, but it is mainly an active component in the metallurgical processes. The slag serves to bind substances which are not desired in the steel being produced. This enables one to control the composition and thereby give the steel improved properties.
2. Alloying elements: Steel is an alloy with iron as the base material. All steel includes small quantities of e.g. carbon, silicon and manganese.
During the production process, alloying elements are elements are added e.g. chromium, nickel, molybdenum and vanadium, often in the form of ferrous alloys (ferrosilicon, ferromanganese, ferrochromium and ferrovanadium, etc). This is how the preconditions are created for imparting the desired for properties to the steel: for example, corrosion resistance, hardness, abrasion (wear) resistance and toughness.
3. Coal: Charcoal was originally used in the production of iron. Charcoal was produced from the combustion of wood in kilns (wood stacks). Today mineral coal is mainly used, but it cannot be utilised directly in the blast furnaces. For this reason the coal is carbonised which implies the removal of water and volatile matter. In this way the coke (carbonised coal) acquires the strength that is required in the blast furnace.
The carbon’s main function in iron production is to act as a reducing agent to convert the iron oxide to iron. But the coke also has further functions: to act as a physical support material for the blast furnace charge, to raise the carbon content in the iron and to supply energy.
4. Scrap metal: Iron and steel scrap is used as a secondary raw material, both for scrap-based and ore-based steel production. The scrap is sorted into different classes and the steel plants utilise a mixture of the types of scrap that best suit the steel that it is intended to produce.
Scrap can be divided into three categories depending on origin:
Internal scrap is scrap that falls to the floor within the plants during steel production and that is directly recovered for the production process. This scrap has the advantage that its precise content is known.
Engineering workshop scrap is the scrap that arises during the working of steel in workshops, within the construction industry, on bridge building etc.
Scrap metal collection is the scrap collected from end-of-life products e.g. on demolition of structures and installations and from households. The scrap may include everything from bridge beams to household utensils.
5. Iron ore: Iron occurs very rarely as a pure metal in the earth’s crust. On the other hand, there is plenty of iron which is chemically bonded, in association with other elements such as oxygen and sulphur. The most abundant elements in the earth’s crust, in named order, are: oxygen, silicon, aluminium and iron.
For the extraction of metallic iron, the compounds formed between iron and oxygen, so-called oxides, play a wholly dominant role. The iron ore mineral is called magnetite (black ore) or hematite (bloodstone ore), depending on the type of oxide of which it is composed.
Magnetite has acquired its name through its magnetic properties. When it is scratched against an uncoloured surface a black streak is formed. Its chemical formula is often written Fe3O4, but since it is a mixed oxide it is more correct to write FeO • Fe2O3. Hematite or bloodstone ore, Fe2O3, has acquired its name from the blood red streak that is formed when scratched.
After mining, the material is crushed and subsequently the ore is separated from the gangue in a process known as ore dressing. In the case of magnetite ore this takes place through magnetic separation. The processed product is called dressed ore or concentrate. The dressed ore can then be shaped and agglomerated into pellets, small marble-like balls with a specific composition, size and strength. Alternatively, the dressed ore can be used to produce iron-rich sinters i.e. semi-fused and solidified lumps of iron oxide.
five ways steel mills brought their raw materials
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