TMT: 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.
HYSD: When expanded, HYSD stands for High Yielding Strength Deformed Steel; 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
Mentioned below are the 10 reasons why you should prefer TMT bars over HYSD bars
1- Mild Steel bars were earlier used for small scale construction due to low yielding strength but later High yielding strength deformed bars were invented for reinforcing heavy structure scale construction.
2- As the scale of construction grew further and need for durable structures arose which HYSD bars were unable to meet, TMT bars were invented with better quality in Bendability, Weldability, Fire resistance, Corrosion Resistance and High Dimension Tolerance.
3- TMT bars have stronger external layer when compared with HYSD due to ductile microstructure at the core and hard crystalline exterior surface of TMT steel.
4- TMT bars have less residual stresses and more tensile strength compared to HYSD bars.
5- TMT bars have better corrosion resistant properties than HYSD bars due to rapid quenching and tempering in the fracturing process.
6- TMT bars have the lowest occurrence of surface flaws compared to HYSD bars because it doesn’t involve twisting or torsional stress.
7- TMT bars can be used in various types of construction works due to amazing flexibility and ductility which HYSD bars cannot provide.
8- Using TMT bars can help to reduce consumption of steel by 8% to 11% compared to HYSD bars used for the same construction.
9- Ductile TMT bars are effective in the earthquake-prone zone with the higher sudden load absorption capacity than HYSD bars.
10- TMT bars give longer life to the structure as the TMT steel doesn’t react with the concrete, forming rust that occupies more space and makes cracks in the concrete.