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).
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. TMT bars were better in every metric when compared with HYSD bars. TMT bars 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 reasons listed below, we can see how TMT bars are a better choice.
TMT Bars are better because:
- TMT bars do not surface flaws when compared with HYSD bars as unlike HYSD bars, as the manufacturing process in the TMT bars does not involve twisting or torsional stress.
- When compared with TMT bars, HYSD bars increase the consumption of steel by 8% to 11% when used in the same construction.
- TMT bars come with a stronger external layer, something which is missing in HYSD due to ductile nature of the core and hard crystalline surface of TMT steel.
- When compared with TMT bars, HYSD bars cannot provide flexibility and ductility, thus limiting their use in different types of construction works.
- TMT bars have less residual stress due to the better manufacturing process and have better tensile strength when compared with HYSD bars.
- TMT bars are effective in earthquake-prone zone and cope better with sudden load surges and absorption when compared with HYSD bars.
- TMT bars are more corrosion resistant when compared with HYSD bars, this is mainly due to rapid quenching and tempering used in TMT bar manufacturing process.