Iron and steel are two distinct materials. Though they are similar in many ways, there are many differences. Steel contains iron, but is not considered a type of iron.
Iron in its purest form was produced only in modern time and has very limited use. The iron tools and weapons of our ancestors were actually made of wrought iron. Wrought iron is a finished product. It is ferrite with small amounts of carbon and other elements as well as some impurities called slag. The slag is iron silicate. It is too expensive to separate it from the pure iron. It is also actually beneficial. The slag reduces the hardness of iron and increases the malleability.
Iron is an element. The iron silicate and pure iron are distinct elements, bonded only by a physical association.
The earliest known use of iron dates back to Egyptian tools make in 3000 BCE. The iron then used was wrought iron that is no longer used commercially. By 1000 BCE the Greeks had developed the technique of making hardened iron weapons. In India the Qutub Minar, a pillar made of 98% wrought iron was constructed in the 4th century AD. The pillar has been standing, exposed to the elements, for 1,600 years and there is no trace of rust or decomposition. Wrought iron is the only known ferrous metal to contain siliceous slag. It is the slag that makes the wrought iron highly resistant to corrosion.
The early form of wrought iron is called Charcoal Iron as it was made in a charcoal fire. The term wrought is the medieval past tense of the word verb ‘to work’. Wrought iron means worked iron. Blacksmiths worked the iron using hammers and heat
Wrought iron continued to serve mankind till 1,400 CE. At this time furnaces used in the smelting process became bigger. Iron was placed at the top of the furnace and reduced to metallic iron. This was processed with coke and carbon gasses to produce various alloys.
Steel is an alloy. An alloy is produced when two metals are fused on a chemical level. Steel is an alloy of iron and carbon. It does not contain the impurities found in iron. Steel can be further processed to obtain various types of alloys. When chromium is added stainless steel is produced which is a highly durable and does not rust.
Steel contains less than 2% carbon as compared with pig iron that has more than 2% carbon. Iron has very minute traces of carbon, approximately 0.12%.
The presence of carbon in steel makes it stronger than iron. Steel also has better tension and compression properties than iron and is therefore favoured in the construction industry. However, steel is less flexible than iron.
Steel can be worked both directly and indirectly. True tempering can only be done with steel. It can be forged with red heat or liquefied casted and moulded. Steel is amenable to heat treatment due to the higher carbon content.
The higher carbon content of cast iron makes it stronger than wrought iron but reduces its malleability and ductility. Cast iron can only be worked by liquefying and cast forming.