Before TMT bars and HYSD bars, mild Steel bars were earlier used for small-scale construction. They were not strong, low tensile strength or even bendability. To correct these, HYSD or High yielding strength deformed bars were introduced for reinforcing heavy structure scale construction. As the scale of structures began to touch the sky, both literally and metaphorically, problems associated with HYSD bars gave way to TMT bars. Its is much better in every metric when compared with HYSD bars. They are better in Fire resistance, Corrosion Resistance, High Dimension Tolerance, Weldability and most importantly Bendability. In a physically perfect world, HYSD would be the better choice but due to the reasons listed below, we can see how TMT bars are a better choice.
While TMT stands for ‘Thermo Mechanical Treatment’, the name is basically their process of protection and HYSD means ‘High Yielding Strength Deformed’ which is their main characteristic when compared with other rods. HYSD bars can be further divided into Torsed / twisted steel (TOR Steel Bars) and Cold Twisted Deformed Steel Bars (CTD Steel Bars).
What are TMT Bars?
Thermo Mechanically Treated or TMT bars are high-strength reinforcement bars having a hardened outer core and a soft inner core. They are manufactured under a process called Thermo Mechanical Treatment, after which they are named.They are manufactured by passing hot rolled steel billets through water, which hardens the surface and increases its tensile strength while the inner core stays at a comparatively warmer temperature and hence, the core becomes more ductile. This variation in the microstructure of the cross-section of the bar provides huge strength to the bar. Since there are no twisting or deformation processes employed in this method, TMT bars have no surface cracks or other defects as well.
What are HYSD Bars?
When expanded, HYSD stands for High Yielding Strength Deformed Steel, as stated earlier; and is also their main characteristic. HYSD steel also undergoes heat treatment similar to TMT bars, but the subsequent processes are different. In this type of steel, after undergoing the heat treatment process, the hot steel rods are either heat rolled or cold twisted for shaping, thus making them both thermally and mechanically treated.
Differences between These Two
Some of the major differences between these two bars are like:
- These bars have preferred corrosion-resistant properties over HYSD bars because of rapid quenching and tempering in the manufacturing process. TMT bars have a stronger external layer when compared with HYSD due to ductile microstructure at the centre and hard crystalline outside surface of TMT steel.
- Due to the amazing flexibility and solidness shown by TMT bars, they can be utilized for a wide scope of development works and is essentially one of the essential reasons why development labourers depend significantly more in this bars when contrasted with HYSD steel bars. Utilizing TMT bars for development assists with lessening the utilization of steel by 8% to 11% when contrasted with HYSD bars for a similar development, again expanding their moderateness.
- TMT bars have the lowest occurrence of surface defects contrasted with HYSD bars since it doesn’t include twisting or torsional stress.
- The manufacturing process of TMT bars doesn’t include contorting or torsion, not at all like HYSD bars which make them a progressively dependable choice. Mild Steel bars were prior utilized for little scope development because of low yielding quality however later High yielding quality twisted bars were created for strengthening substantial structure scale development. Be that as it may, with increment in the size of the development, TMT bars were presented which guaranteed better quality, opposition against erosion and fire, progressively bendable and had more resilience limit overall. TMT bars give longer life to the structure as the TMT steel doesn’t respond with the solid, shaping rust that consumes more space and makes splits in the solid.
- These TMT bars are superior to HYSD because of lesser residual stresses, more corrosion resistance because of hard surface and greater ductility for similar strength grade.
- TMT steel bars manufacturing process includes hot rolled steel wires going through water. This makes the surface hard and keeps the centre hotter and milder. This aids in making the steel erosion safe and furthermore makes welding simpler. Where HYSD bars are both hot or cold worked due which it is somewhat harder to weld than TMT.
- TMT bars have no surface distortions contrasted with HYSD bars. Thus TMT bars are perfect for use in basic frameworks for a better quality of the structures.
- TMT bars have a higher burden-bearing limit than HYSD bars. This assists with lessening the number of bars required for building a structure along these lines decreasing the expense of development. TMT bars are more flexible than HYSD bars. This results in more noteworthy adaptability permitting more space for stylish planning of a structure.
- TMT bars have less residual stress and higher elasticity because of the better assembling process. These are successful in seismic tremor inclined zones and it adapts better to abrupt burden floods and ingestion when contrasted and HYSD bars. Because of its different highlights, it is most appropriate for a wide range of construction purposes.
- Due to rapid quenching and tempering done during the manufacturing process, TMT bars have better erosion opposition, when contrasted with HYSD, which are dull. Because of its predominant erosion opposition, TMT bars are utilized to fabricate solid structures in waterfront zones where the stickiness is high.
- TMT bars have high-pressure yield and the ability to withstand unexpected burdens than HYSD bars consequently they are profoundly appropriate for development in zones with incessant or high seismic movement including seismic zones.
- As the size of development became further and the requirement for solid structures emerged which HYSD bars couldn’t meet, TMT bars were concocted with better quality in Bendability, Weldability, Fire obstruction, Corrosion Resistance and High Dimension Tolerance.
- TMT bars have a stronger external layer when contrasted with HYSD due with malleable microstructure at the centre and hard crystalline outside surface of TMT steel.
The variation in the micro structure of a TMT bar makes it exceptionally reasonable for high quality construction work. TMT bars are greatly improved at withstanding torsional stress making them profoundly erosion safe contrasted with lower levels of steel development bars. HYSD bars are created by the mechanical curving of the steel bars directly in the wake of throwing, subsequently bringing about surface blemishes. This progression brings down the general quality obstruction of the HYSD bars. Both hot rolled and cold worked HYSD bars were utilized as a superior quality option in contrast to the previously utilized mellow steel bars however as they contain surface disfigurements inclined to mileage, they prompted the improvement of TMT bars.
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