The core difference
Both TMT (Thermo-Mechanically Treated) and HYSD (High-Yield Strength Deformed) bars are reinforcement steel for concrete construction, but the manufacturing process and resulting properties are meaningfully different.
TMT bars
Produced by rapid water-quenching the hot rolled bar and then letting the core temperature temper the outer layer. The result: a tough martensitic outer ring with a ductile ferrite-pearlite core. Excellent for earthquake-prone regions because the bars can bend without snapping.
HYSD (cold-twisted) bars
Cold-worked to increase yield strength. Cheaper to produce but more brittle, especially at bends, and reduced corrosion resistance versus TMT.
What most Indian projects use today
TMT Fe 500 D and Fe 550 D dominate high-rise, bridge, and infrastructure projects. HYSD is largely phased out of new IS-code-compliant work. If your BOQ still specifies HYSD, get it re-evaluated - swapping to TMT is usually cost-neutral and gives better safety margins.
Compare TMT prices from steel manufacturers across North India, Central India, and Eastern India on The Loha Bazaar marketplace.