TMT stands for Thermo Mechanically Treated. The TMT bars have a hard outer surface and a softer core. Their manufacturing process includes hot rolled steel wires passed through water. This makes the surface hard and keeps the core warmer and softer. This helps in making the steel corrosion resistance and also increase its weldability. Thermo-mechanically treatment (TMT) is a process that takes the round steel stock and softens it in a furnace and is rolled has it is taken out and quenched in water to create a “martensite ,” which is a process of hardening steel.  The result is a stronger, more corrosive resistant steel rebar than other rebar types. On the other hand, HYSD stands for High Yielding Strength Deformed bars. These bars have more yield strength than Mild Steel. Unlike TMT bars, HYSD bars are both hot or cold worked. They are graded as Fe 415 or Fe500.