Iron has been, since its origin, one of the metals that have contributed the most to civilisation, allowing a qualitative leap in terms of constructions and tools. It has been a reference metal and has been very present throughout history for more than 6,000 years. So, in this blog post, we will explain the most common types of iron.
Types of iron
Iron is the most commonly used hard metal, but in its pure state it does not have many applications except if its magnetic potential is used. This material is frequently used in the formation of iron and steel products, as the main element or with other alloys, both metallic and non-metallic.
This is basic crude iron, which is made by heating iron ore in a furnace. Inside the furnace, the iron ore chemically reacts with coke and limestone. Pig iron contains approximately 90-95% iron, 3-4% carbon and traces of other elements such as silicon, manganese and phosphorus, depending on the ore used. It is much harder than pure iron, but still too weak for use.
Because of these characteristics, pig iron is considered more of a raw material than a finished or semi-finished product, and is considered only an intermediate stage in the manufacture of steel or cast iron.
Among its applications, we can summarise them mainly in three:
- As feed for the mixer from which it passes directly to the refining furnaces.
- As pig iron billets, ingots which, once cooled, can be stored while awaiting re-melting to produce steel or iron castings.
- Used for direct casting of castings, although it can only be used for items that do not have to withstand structural loads or high pressures.
Cast iron or cast iron is an iron-carbon alloy with a high carbon content of about 3-4%, just like pig iron. This makes it an extremely hard and brittle material, which makes it impossible to shape even when heated. On the other hand, it oxidises relatively easily. Its usefulness derives from its relatively low melting temperature.
Within cast iron, we can distinguish soft cast iron, grey cast iron and ductile cast iron. White cast iron has carbide impurities that allow cracks to propagate directly. Grey cast iron has graphite flakes that deflect a passing crack and initiate countless new cracks as the material breaks. Ductile cast iron has spherical graphite nodules that prevent the crack from advancing further.
Wrought iron is a material formed by mixing liquid iron with some slag (waste). The result is an iron alloy with a much lower carbon content (between 0.05% and 0.25%).
Wrought iron is thus softer than cast iron, and also much less tough, so it can be heated to shape relatively easily, and is also less prone to rust than cast iron.