Steel

Today, steel is one of the most common materials used in the world, over 1.3 billion tons are produced every year. Steel is an alloy which consists of iron and carbon content between 0 .2% to 2.1% by weight, depends on the grade. Carbon is the commonly used alloying material for iron; various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten.  Carbon and other elements act as a hardening agent for iron. The amount of varying alloying elements and their presence in the steel controls qualities such as; hardness, ductility and tensile strength.  Steel with more carbon content can be made stronger and harder than iron, but that kind of steel is less ductile than iron.

Alloys with carbon content greater than 2.1% are called cast iron, due to their lower melting point and castability.  In the mid of 19^th century Bessemer process was invented, Due to this invention  steel became an inexpensive mass produced material. It is majorly getting used in buildings, infrastructure, ships, automobiles, machines and weapons.

Heat treatment

Annealing, quenching and tempering are the common types of heat treating process available to steel.  Annealing is the process of heating steel to a required high temperature to soften it. Annealing has three phases: recovery, recrystallization and grain growth. Quenching and tempering will heat the steel in austenite phase first, then quenching it in Water or oil. This rapid cooling will results in hard and brittle martensitic structure.

Steel production

When iron is smelted from its ore, it contains more carbon .It should be melted and reprocessed to reduce the carbon to the correct amount, at that point other elements can be added to become steel. Normally 96% of steel is continuously cast and only 4% is cast steel ingots. The ingots are then heated in a soaking pit and hot rolled into slabs, blooms or billets. Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such as i-beam and rails.

Steel Industry

The steel industry is considered as a marker for economic growth, because of the critical role played by steel in infrastructural and overall economic development. The economic boom in china and India has produced the massive demand for steel in recent years, from 2000-2005 worlds steel demand had increased by 6%. In the year 2005, the survey from British geological stated that, china was the leading top steel producer about one third of the world share.

Questions:

• Explain steel?
• Explain Annealing, quenching and tempering?