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Everything you need to know about 550D TMT Bars

Updated: Jun 30


The 550D TMT Bar is a type of Thermo Mechanically Treated (TMT) steel bar, classified according to IS:1786, where Fe represents Iron. Iron is the primary metal used in manufacturing these bars. The number '550' indicates the minimum yield stress in MPa (the tensile stress needed to cause total elongation), while the letter 'D' signifies ductility. In essence, this means that TMT steel bars of 550D grade exhibit increased tensile strength and elongation.


Structures such as dams, railway bridges, flyovers, stadiums, skyscrapers, airports, industrial buildings, windmills, ports, hospitals, tunnels, concrete roads, malls, multiplexes, and other load-bearing constructions require 550D TMT steel bars due to the heavy loads they bear.


Why 550D TMT Steel bars?

In earthquake-prone regions, 550D TMT steel bars are commonly utilized due to the high seismic resistance of D grade steel. The reduced levels of carbon, sulfur, and phosphorus in Fe550D TMT steel bars aid in steel preservation and earthquake shock resistance.

TThis happens because the TMT manufacturing process results in a steel product with a tough exterior shield that gives the necessary strength to the TMT steel bar, along with a flexible inner core that provides the necessary flexibility to endure the intense shaking of the earth during an earthquake.


Difference between Fe 550 and Fe 550d steel

With the increasing need for high-rise construction and critical infrastructure projects, it is essential to use very strong and stable steel bars that help building structures withstand the effects of time, seismic activity, temperature changes, natural disasters and more. can do. Grades Fe 500 and Fe 550d are increasingly being used today for the manufacture of a wide variety of objects. Check out the best tmt Bar in India


Fe 500 is good – due to high seismic resistance and ductility. Fe 500 can be used in a wide variety of multi-story commercial and residential projects. They have a high degree of ductility and strength and are specially made to give stability to high rise structures. They can withstand loads much better and are useful in all areas with sudden loads or high seismic activity.


The Thermo Mechanical Treatment involves 3 steps:

  1. Quenching

  2. Self-tempering

  3. Atmospheric cooling

The first stage of primary steel making takes place in an oxygen furnace. Oxygen is combined with the carbon in the iron to remove the carbon dioxide. Next, it is passed through the EAF (Electric Arc Furnace) for further refinement of the composition of the metal. Molten steel from EAF is transferred to a ladle and then to a Continuous Casting Machine. Liquid steel flows out of the ladle into the casting ladle and then into a water- cooled mould. Here, the molten steel gets solidified and steel billets come out continuously from the CCM in the required length. Once the hot rolled bars are released, they are treated to a water spray system known as the Thermex System. The jets of water cool the outer layer of the bars rapidly and harden them, forming a martensitic outer rim. The core of the bars continues to be molten at this stage. This cooling technology is known as Quenching.


The hot inner core allows heat to flow from inside to the surface causing tempering of the outer Martensite layer, thereby forming a structure called ‘Tempered Martensite’. This process is called


Self-tempering. Once the self-tempering is complete, the bars are further cooled on a cooling bed under normal room temperature. During this process called atmospheric cooling, the soft, molten core turns into a ferrite-pearlite structure which is ductile and soft. This process called


Atmospheric cooling increases the tensile strength and makes the steel bars highly ductile and weldable.


550D grade TMT bars are preferred for building critical infrastructure in the country for the following properties of these bars:


Earthquake resistance: TMT bars offer earthquake resistance thanks to their soft pearlite core. 550D TMT bars are capable of withstanding seismic and dynamic loads. TMT bars exhibit excellent fatigue resistance to seismic events, making them suitable for construction in earthquake-prone regions.


High elongation: TMT bars can elongate up to 50% more than the original length without compromising on the measurements. This is again a desirable property

Corrosion and rust resistance: TMT bars are resistant to corrosion and have moisture resistant properties. As a result, they can be used in constructions such as bridges, dams, canals and sewages, where they may be exposed to water as well as salinity in the groundwater


Flexibility and bendability: TMT bars have excellent capacity for bending, so they can be moulded into different aesthetic shapes and architectural designs


Fire resistance: The top-quality TMT bars produced by the best TMT steel bar manufacturers in India exhibit excellent thermal stability, capable of withstanding temperatures between 400 and 600 °C. This ensures the safety of the occupants residing in buildings constructed using TMT steel bars.


Fatigue Resistance: A unique feature of TMT Bars are their High Fatigue Resistance on dynamic loading on account of the high strength of the surface layer. Weldability: TMT Bars with low carbon equivalent content can be used for butt/ lap and other weld joints without reduction in strength at the weld joints.

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