The TMT bars that are used by top steel manufacturers in strengthening the foundation of the country’s infrastructure goes through various stages before it achieves the required form. Let us travel along with iron ore through its journey from ore form to steel to eventually become TMT bars produced by TMT bar manufacturers of the country.
- Processing of raw iron ore into molten iron – Smelting
Raw iron ore is sourced from select locations along with coal, limestone and dolomite. The iron ore is then beneficiated to increase the grade of it and also increase the iron content in it. Then the iron ore fines are agglomerated which is where they are formed into lumps of appropriate size through processes called sintering and pelletizing.
Beneficiated iron ore, coke, limestone and dolomite is then fed on top of the blast furnace. Hot air is then injected through the nozzles that are at the base of the furnace. This results in iron ore and sinter melting and collecting at the bottom of the furnace as a molten pool. It is the carbon and carbon monoxide in coke that helps in chemical reduction of iron oxides in the ore to become molten iron.
In the process, limestone combines with impurities from the iron ore and sinter, forming a liquid ‘slag’ which, being lighter, floats on top of molten iron as it is lighter in density.
- Conversion of molten iron into steel
In the second stage oxygen is blown into the furnace and it combines with carbon in the iron. With this pretreatment carbon is eliminated in the form of carbon dioxide. This is steel in its raw form. It is an alloy of iron and carbon containing less than 2% carbon. Further heating is done to refine the chemistry and composition of steel. Alloy additives are used to arrive at the desired chemical composition.
The journey of raw molten steel into TMT steel bars starts when molten steel is gradually transferred to the continuous casting machine to form billets.
- Raw steel into TMT Bars
Following which, the billets are immediately passed through a process called quenching where they are rapidly cooled to acquire certain properties. With this process the surface hardens while leaving the core hot and soft. The core would continue to supply heat to the surface and cause the self tempering of the outer layer to become martensite. The core stays austenitic at the stage.
In the next stage the bars go through atmospheric cooling and then the austenitic core gets transformed into a ductile ferrite pearlite structure. The final structure, thus, is a perfect combination of a strong outer layer (tempered martensite) with a ductile core (ferrite) and is called the TMT Bar.
The TMT process (Thermo mechanical treatment) used by the steel bar manufacturers brings in a lot of advantages to the steel bar. TMT bars can withstand bending and rebending due to low carbon content and higher elongation. They are safe and economical due to their bendability, weldability and ductility. Retention of strength due to martensite outer layer, earthquake resistance due to soft ferrite pearlite core, ease of welding , anti corrosive properties and superior bonding strength between bar and concrete are the other benefits that TMT process brings into the steel bars made by TMT steel companies.
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