Iron (Fe) is the chemical element with atomic number 26 in group 8 of the periodic table of the elements. It is one of the most abundant elements in the earth's crust and the second most abundant of the metals.
Iron is extracted from mineral deposits in the form of iron oxide. To produce iron, the oxide has to be reduced in a blast furnace. Coke, limestone and ore from iron ores are added to the blast furnace. The iron in the ore is reduced and chemically oxygen is released from the iron oxide in the ore. This releases the iron. Iron, moreover, cannot be used in its pure state, so it is alloyed to create different types of iron.
Characteristics of iron
- It has a density of 7874 kg/m3 and its melting point is 1538 °C.
- It is silver-grey in colour and is magnetic.
- It is a malleable metal, i.e. it can be rolled into sheets or plates and is tough.
- It is very hard and dense.
It is the most widely used hard metal, but in its pure state it does not have many applications except when its magnetic potential is used. Iron is widely used in the formation of siderurgical products using it as the main element or with other alloys, both metallic and non-metallic. The largest producers of iron are Australia, Brazil, China and Russia.
Steel is considered an alloy of iron if it contains less than 2.1% carbon. If it contains more than 2.1% carbon, it is called cast iron.
Steel has the metallic characteristics of iron in its pure state, but the addition of carbon and other metallic or non-metallic elements improves its physicochemical properties, especially its strength. They are classified according to their carbon content:
- Low carbon steels (<0.25%). They are soft but ductile. They are used in vehicles, pipes or structural elements. There are also high-strength and low-alloy steels, which contain other elements up to 10% by weight; they have greater mechanical strength and can be worked very easily.
- Medium carbon steels (0.25%-0.6%). They are heat-treated to improve their properties. They are stronger than low carbon steels, but less ductile. They are used in engineering parts requiring high mechanical and wear resistance.
- High carbon steel (0.6%-1.4%). They are even stronger, but less ductile. Other elements are added to form carbides, e.g. tungsten is used to form tungsten carbide. These steels are mainly used in tools.
- Alloy steels (carbon + other elements). It is impossible to meet the demands of today's industry with unalloyed steels. Therefore, in order to achieve certain characteristics of resilience, wear resistance, hardness and resistance to certain temperatures, we must resort to these alloys. In this way we introduce chemical and structural modifications that affect hardenability, mechanical characteristics or resistance to oxidation.
Iron-carbon alloy cast irons have a carbon content of between 2.15% and 6.7% and contain other alloying elements such as manganese, phosphorus, silicon, oxygen and sulphur. There are different types of cast iron:
- White cast iron: composition with carbon and silicon. They are known as unweldable.
- Grey cast iron: the carbon is in the form of flakes and is therefore weldable.
- Nodular/ductile cast iron: contains magnesium in its structure. It has good mechanical properties similar to carbon steel.
Iron, like many other metals, is easy to recycle because it does not lose its qualities. The problem arises because it has contaminants. Iron is melted down in special furnaces and the pure iron is extracted so that it can be reused. Iron scrap often comes from old cars (end-of-life vehicles) and household appliances (electronic scrap).
The recycling of this metal is very important to reduce greenhouse gases. There are 4 main stages in metal recycling:
- Collection: delivery of metal waste to companies dedicated to its collection.
- Processing: sorting according to the composition of the material.
- Fragmentation: shredding the metals and compacting them.
- Distribution: sale to industry that can make use of the recycled metals.
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