Steel has been a vital tool for mankind since its inception. Steel is the major component in almost everything starting from buildings, bridges, automobiles to pieces of machinery. Discovery of steel and it’s production dramatically changed the economic status of the world. Steel is an alloy of Iron and Carbon in which the carbon content is at 2% (Above 1%, it is classified as Cast Iron).
A Little history
Steelmaking has been done since ancient times, especially during Iron Age, in Ancient China, Rome, Srilanka and even in India. For a majority period of time, steel was produced in bloomer furnaces which were replaced by new methods in the late 17th century. Modern steel industry began in the late 1850s. The production of inexpensive steel was introduced by Henry Bessemer in his method known as the Bessemer process. This process was done by introducing oxygen into molten iron in order to reduce the carbon content.
The bessemer process was replaced by newer methods namely Open hearth process. Currently steel production makes use of recycled materials as well as traditional raw materials, such as iron ore, coal, and limestone. Two processes, Basic Oxygen Steelmaking (BOS) and Electric Arc Furnaces (EAF), account for virtually all steel production.
Steel as a reinforcement
The application of steel acting as a reinforcement for concrete in constructions was a major breakthrough. The purpose of reinforcement is to support tensile strengths which, the concrete alone cannot provide. Therefore by adding steel bars along with concrete produces the Reinforced Cement Concrete (RCC) structure in which the concrete provides the compressive strength and steel provides tensile strength.
The concept of reinforcement was introduced in the 19th century by French industrialist François Coignet. He was the first person to use iron-reinforced concrete as a technique for constructing building structures. Even though iron bars were used as reinforcements, it was prone to corrosion quickly, due to which it was unsuitable for reinforcement. This prompted for a newer form of reinforcement which could be resistant to corrosion.
The iron bars were replaced by a newer type of steel rebar called the Mild Steel (MS) rebars. Unlike normal iron bars, Mild Steel is an alloy of iron, carbon, sulphur and other components which has a greater tensile strength. Mild Steel rebars had better ductility, bendability, workability and corrosion resistance. This was achieved due to the low carbon content present in Mild Steel rebars.
Mild steel bar
Mild Steel rebar had more tensile strength than iron bars, having a grade of Fe 250, where 250 is the maximum yield strength in N/mm. But the need for a better reinforcement soon arose as the mild steel reinforcement bars couldn’t provide the tensile strength the new world construction demanded. As newer technologies were introduced in constructions, steel makers used these technologies to produce higher strength steel reinforcement bars. One such steel rebar was the Higher Yield Strength Deformed (HYSD) steel rebar. Read on about the evolution of reinforcement bars from mild steel to HYSD and finally the TMT processed steel bars on the next blog.