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  • Writer's pictureAvantika Rana

What is a TMT Bar? Why do we need it for construction?

Have you ever visited a construction site and wondered why those corner pillars have iron rods embedded in them?

What are TMT bars?  Need in the construction?

These twisted Iron rods are called TMT bars, and TMT stands for Thermo Mechanically Treated bars.

Let us break it up to you in a simple way!

TMT is a series of unique thermomechanical processes to make durable steel rods using modern metallurgy science.

  • TMT bars are iron/steel rods which are thermo mechanically treated to give better ductility, strength and bendability.

  • These TMT bars are often used in construction projects to provide the needed support and stability.

  • TMT bars acts as a backbone of a structure.

What is the process of Thermo Mechanically Treatment?

Basically, the TMT process helps the rods become tough on the outside and soft on the inside. This is because the variation of temperature gives two layers of steel.

TMT bars are made up of two layers:-

  • Tough outer core- Gives ductility, strength and hardness

  • Soft inside core- Gives flexibility with better bendability

Metallurgically there are three allotropes of iron which are responsible for giving the desired TMT bars.

Three Allotropes of iron

1. Austenitic- Roughly it is a molten liquid solution of iron with carbon that exists above critical eutectoid temperature of 727 °C.

This is a necessary material to start the TMT process. It is a liquid iron solution with carbon compounds to give concrete strength to the bars.

The making of hard core and soft core depends on the way we reduce its temperature.

2. Martensite- Rapid cool down - Very Hard in nature

When Austenitic goes through sudden quenching, it results in drastic temperature change. This temperature change is responsible for the tough outer layer of the steel bar. And this results in a tough and durable TMT bar.

Reason- Because the cooling rate is so sudden, carbon does not have enough time for diffusion. Therefore, the martensite phase consists of a metastable iron phase oversaturated in carbon. The more carbon a steel has, the harder and more brittle it becomes. This is why martensitic core is very hard and brittle.

3. Ferrite-Pearlite - Gradual cool down at atmospheric temperature. - Soft in nature

When the Austenitic is slowly cooled down, it turns into Ferrite-Pearlite mass. This Ferrite- pearlite mass is soft in nature and is responsible for giving great tensile strength and elongation. The yield and tensile strengths of TMT bar increases with increase of pearlite content in the inner core.

Also, due to the absence of cold stress and the carbon presence, the bar becomes corrosion-resistant and uplifts its weldability.

Why choose TMT bars for construction?

  1. TMT bars do not carry surface deformities and give better strength to structures.

  2. TMT bars can bear a sudden stress load. Thus, making them an excellent choice to use in seismic zones like 3, 4 and 5.

  3. TMT carries great ductile strength- Which gives a free hand to build unique design structures.

  4. TMT process makes them corrosion-resistant thus are used in constructions like dams, bridges or canals. (Frequent contact with water)

  5. Due to numerous properties of strength, they give longevity to the structures in future.

  6. TMT plays a vital role in reinforcing the concrete to avoid cracks.

  7. TMT bars are fire resistant and can resist fire to up to 1000 degree Celsius.

  8. TMT bars are cost-effective and feasible when compared to other steel bars. Despite the fact that there are many types of steel bars available in the market, but none supports the structure in terms of better strength, effectiveness and anti-corrosive nature like TMT bars.

Here is a guide which can help you buy the best TMT in the market-

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