MT Bars (Thermo Mechanically Treated Bars)

TMT Bars,Thermo mechanically treated bars are high strength deformed steel bars used in reinforced cement concrete (RCC) work manufactured with the help of advancement of technology. TMT bars are latest production in MS steel bars and have superior properties such as strength, ductility, welding ability, bending ability and highest quality standards at international level.

What is thermo mechanically treatment process?

By adopting thermo mechanically treatment process higher strength of TMT bars is obtained. In this process, steel bars get intensive cooling immediately after rolling. When the temperature is suddenly reduced to make surface layer hard, the internal core is hot at the same time. Due to further cooling in atmosphere and heat from the core, the tempering takes place. This process is expected to improve properties such as yield strength, ductility and toughness of TMT bars. With above properties, TMT steel is highly economical and safe for use. TMT steel bars are more corrosion resistant than Tor steel.

How to get higher strength of TMT bars?

Generally, higher strength of TMT bars can be obtained by increasing carbon content, micro alloying, and thermo mechanically treatment or cold twisting. So far in India, cold twisting of bars is extensively used for the production of high strength bars. The two main ribs become helical when cold twisting process is done whereas these ribs in hot rolled bars are straight. The excess of carbon content threatens its property of welding ability.

In TMT bars, this problem has been eliminated. In these bars, carbon content has also been brought down leading to improved ductility and can be restricted to 0.2% to attain welding ability and at the same time no strength is lost. The joints can be welded by ordinary electrodes without any extra precautions.

Features of TMT Bars

Better ductility and malleability
High yield strength and toughness
More bonding strength
Earthquake resistance
Corrosion resistance
High thermal resistance
Economical and safe in use
No loss in strength at welded joints
Ordinary electrodes used for welding the joints

Caution

While purchasing TMT bars, notice identification mark on these bars from manufacturing firm.
For big projects it is advised to check that only one type/grade of bars is brought to the site and is used in the project after conducting test for each lot. Do not use mixed, 2 or 3 types/grades bars in RCC work at one work.

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HSD Steel Bars (High Strength Deformed Bars)

High strength deformed bars IS: 1786-1985 are steel bars which are provided with lugs, ribs, projection or deformation on the surface and are produced in form of cold twisted deformed bars. These bars are extensively used for reinforcement purposes in a construction. Due to ribs or projections on the surface, these steel bars minimize slippage in concrete and increase the bond between two materials i.e. between cement concrete and steel bars.

The deformed bars have more compressive and tensile stress than that of mild steel plain bars. High strength deformed bars have improved anchorage; therefore they can be used without end hooks or bent up ends of bars. This reduces labor for fabrication of steel reinforcement. The deformation is spaced on bar at uniform distances. These bars are produced in sizes or sections from 4 mm to 50 mm in diameter.

Generally cracks develop in reinforced concrete around mild steel bars due to stretching of bars, loss of bond under the load. To minimize this problem, deformed bars having projecting ribs or twisted surface which improves the bond with the concrete should be used in RCC work.

Features of HSD Bars

Low carbon value: HSD Bars have lower carbon level, resulting in good ductility, strength and welding ability.
Superior bonding strength: HSD bars are well known for their excellent bonding strength when used with concrete.
Welding capability: Since these bars have lower carbon content, they have 100% welding capability than conventional bars.
High tensile strength: HSD bars feature high tensile strength. They offer great asset in construction process, where a lot of bending and re bending is required.
Wide application range: These bars have wide application range like in building residential, commercial and industrial structures, bridges, etc.
Satisfactorily malleability, minimum weight and maximum strength and suitable for both compression and tension reinforcement.

Process of production of bars

The main process for production of bars is hot rolling followed by cold twisting. Latest technological advances in the field of micro-alloying of steel and thermo-mechanical treatment process have resulted in the production of deformed bars as reinforcement for use in cement concrete in three grades namely Fe 415, Fe 500 and Fe 550.
The strength of bonds of deformed bars
In addition, the calculated strength of bonds of deformed bars should be 40 to 80 % higher than that of plain round bars of same nominal size. Tor steel possesses the strength of 1.5 to 2.0 times of mild steel in compression as well as in tension, whereas it costs only 10% more than mild steel.

Deformed steel bars have minimum 0.2% proof stress or yield stress in N/mm square. Proof stress is the stress at which non proportional elongation equal to 0.2% of the original gauge length takes place. Hence deformed steel bars are very economical to use in RCC work. Structural Engineer recommends cold twisted deformed (Ribbed or Tor Steel Bars) bars as they are best quality steel bars for construction work.

Mechanical properties of high strength deformed (HSD) steel bars for concrete reinforcement

Property	Grade of Steel
	Fe415 Fe500 Fe550
0.2% proof stress/ yield stress minimum N/mm square	415.0 500.0 550.0
Elongation, percent minimum on Gauge length 5.65 VA where A is the cross sectional area of the test piece	14.5 12.0 8.0
Tensile strength, minimum, N/ mm square	10% more than proof stress but not less than 485, 8% more than proof stress but not less, than 545, 6% more than proof stress but not less than 585

What are the benefits of using TMT bars for construction of homes