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What is TMT?news
23 January 2006

Thermo mechanically treated (TMT) steel, can be described as a new-generation-high-strength steel having superior properties such as weldability, strength, ductility and tensility, which meet the highest international quality standards.

Features:

Resists fire: Withstands temperatures up to 5,000C.

Resists corrosion: The TMT process gives the bar superior strength and anti-corrosive properties.

Earthquake resistance: The soft ferrite-pearlite core enables the bar to bear dynamic and seismic loading.

Malleability: TMT bars are most preferred because of their flexible nature

Enables welding: They have fine welding features.

Bonding strength: External ribs running across the entire length of the TMT bar give superior bonding strength between the bar and the concrete.

Cost-effective: A high tensile strength and better elongation value gives you great savings

How TMT steel is prepared:
Under thermo mechanical treatment, the steel bars are passed through a specially designed water-cooling system where they are kept till the outer surface of the bars becomes colder while the core remains hot. This creates a temperature gradient in the bars.

When the bars are taken out of the cooling system, the heat flows from the core to the outer surface, further tempering of the bars, which helps them attain a higher yield strength. The resulting heat-treated structure imparts superior strength and toughness to the bars. The microstructure of the core is a very fine-grained ferrite and pearlite. TMT bars are also known as 'quenched and tempered rebars', because of the quenching and tempering processes involved in making the bars.

The production of quality TMT bar depends on three major factors - quality raw materials, a properly designed and automated mill, and a well-designed quenching and tempering technology. All rebars must be purchased based on the properties of yield strength, tensile strength and elongation values.

Deciding the percentage of carbon content in steel has been a major challenge for engineers. While a minimum level of carbon content in steel is essential to achieve the required strength, excess carbon threatens its weldability. In TMT bars, this problem has been eliminated by restricting the carbon content to 0.2 per cent to attain weldability and ensuring that its strength is not lost. The joints can be welded by ordinary electrodes and no extra precautions are required.

The bars come in different lengths, in sizes of 11 to 12 metres and can be customised to the required specifications. TMT bars that have uniform and concentrated hardened periphery and the softer core will have the desired tensile strengths coupled with high elongation as required in seismic zones. Depending on the size and grade, rebars with hardened periphery of about 15 to 30 per cent of the cross sectional area of the bar are ideal for civil constructions (constructions of houses, offices, etc.)

also see : Hectic year ahead for Kanishk Steel

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What is TMT?