Demystifying Manufacturing Process Of Premium TMT Bars

TMT (Thermo-Mechanically Treated) bars are extensively deployed in construction projects for their superlative strength, ductility, and resilience forming the backbone of bridges, buildings and other structures. But did you ever reflect on how these bars are actually produced? The fascinating manufacturing process of premium TMT bars involves several intricate steps transforming raw materials into these bars of very high quality and performance standards.

The Process

1. Selecting the raw materials

The manufacturing process commences with the careful selection of raw materials, primarily high-quality Iron ore, Coal or Coke, Limestone and Dolomite. The primary source of iron is iron ore. Limestone and Dolomite act as fluxing agents and Coal, used in the form of Coke delivers the fuel required to create high temperatures in the furnace.

2. Sintering

Initially, Iron ore, Limestone and Coke are crushed and sized properly. Then, for optimal performance, the crushed materials are pre-heated and fused together in a process known as sintering. This helps to produce manageable pellets to enhance productivity.

3. Blast furnace

The blast furnace, which is the heart of the manufacturing process of premium TMT bars, uses extreme heat to melt the mixture of iron ore, coke, and limestone. The mixture is added or charged into the top of the blast furnace while a blast of hot air is passed through the nozzles at the bottom of it. The air chemically reacts with the mixture and the reduction of the iron in the ore takes place producing molten metal.  The Limestone mixes with impurities and liquid slag (impurities separated from Iron) is formed which being lighter than the molten metal floats over it. 

4. Steelmaking

The molten iron is transferred to a Converter or a Basic Oxygen Furnace (BOF), where oxygen is blown through it to remove carbon, an impurity. Here Oxygen blends with Carbon in the Iron, forming Carbon dioxide and is eliminated. This is the refinement of Iron into steel. Further purification is done in a Ladle Heating Furnace (LHF) and RH Degasser.

5. Continuous casting

The molten steel is then poured directly into a casting machine, a copper mould cooled by water, where it solidifies into long slabs or billets.

6. Hot rolling

The slabs or billets are moved through a series of rollers, which progressively reduce their thickness and increase length. This process also refines the grain structure of the steel and increases its strength. The temperature used in the rolling mill is between 1200°C to 1250°C.

7. Thermo mechanical treatment

This is an extraordinary process. It is this process which makes the bar develop a tough outer layer (Martensite) with a soft inner core and a Ferrite Pearlite structure. This process remarkably increases the strength and ductility of the TMT bars compared to ordinary ones. 

8. Quenching 

This cooling technology is called Quenching. The products from the finished mill are passed through a microprocessor-controlled Quenching Box-water cooling system. The manufacturing process of premium TMT bars utilizes a water spraying system known as Thermex technology for superfast cooling of the outer core. The process guarantees the ductility of the bars while forming a hard martensitic rim together with a hot Austenitic core and they become super tough and durable.

9. Self tempering 

The bars are subjected to a controlled cooling process that tempers the martensite, significantly decreasing the brittleness and improving overall toughness so that they can tolerate high loads.

10. Atmospheric cooling

After self-tempering, the bars are put on a cooling bed, where they get ready to be cooled at normal atmospheric temperature. This step makes sure that the TMT bars finally possess the required properties like high tensile strength, better ductility, good corrosion resistance and great weldability.

The Benefits

1. Composed of prime steel billets with the help of a controlled process to optimize all constituents, Premium TMT Bars keep exhibiting a Yield Strength of 570 N/mm2 min and a Tensile Strength of 630 N/mm2 min which is a remarkable improvement on the present range of 550D range TMT Bars available in the country, offering a perfect combination of strength and flexibility.  
2. Consistency in weight and length of Premium TMT Bars as per the IS 1786 grade, helps construction professionals and builders to get batch consistency and uniform sectional weight across all construction units while facilitating superlative structural durability.
3. Premium TMT Bars possess unparalleled and matchless shine and finish.
4. The consistent and standard rib area (mm2/mm) metrics of Premium TMT Bars secure an interlock bonding with the concrete so that there is superior stability to the construction area.
5. The premium TMT bars eventually produced can give up to 20% more strength to a concrete structure than conventional steel bars made with the same quantity of steel together with substantial cost savings.