Every TMT quote names a grade - Fe 500, Fe 500D, Fe 550D. The number is strength; the "D" is ductility. Here is what the grades mean under IS 1786, how they differ, and how to make sure you receive what you paid for. The grade itself must come from your structural engineer's drawings.
Fe stands for iron, and the number is the minimum yield strength in N/mm2 - the stress at which the bar starts to deform permanently. D marks a ductile grade: the same yield strength, but stricter requirements for elongation, tensile-to-yield ratio and chemistry, so the bar can bend and stretch further before it breaks.
| Grade | Min. yield (N/mm2) | Min. tensile strength | Min. elongation |
|---|---|---|---|
| Fe 500 | 500 | 1.08 x actual yield, not less than 545 N/mm2 | 12% |
| Fe 500D | 500 | 1.10 x actual yield, not less than 565 N/mm2 | 16% |
| Fe 550 | 550 | 1.06 x actual yield, not less than 585 N/mm2 | 10% |
| Fe 550D | 550 | 1.08 x actual yield, not less than 600 N/mm2 | 14.5% |
| Fe 600 | 600 | 1.06 x actual yield, not less than 660 N/mm2 | 10% |
Summary of IS 1786 mechanical requirements; D grades also have tighter limits on carbon, sulphur and phosphorus. Refer to the current standard for full requirements.
In an earthquake, a well-designed structure is meant to bend, not snap. Bars with a higher elongation and a higher tensile-to-yield ratio can absorb more energy and give warning before failure. That is why many designers specify D grades for columns, beams and joints in seismic zones.
On Indian Steel Portal you float one inquiry for the TMT grade you need - grade, sizes, quantity, preferred makes, delivery city and payment terms. KYC-verified mills, stockists and traders quote against it in a live reverse auction with a minimum decrement and a soft-close, ranked L1 to L4 on landed cost. You award L1 or any ranked bidder, and the deal note - with GST, MTC and weighment terms - is generated for both sides.
Float a TMT inquiry - freeTMT bars and rebarsBoth have a minimum yield strength of 500 N/mm2. Fe 500D must meet higher minimum elongation (16% vs 12%), a higher tensile-to-yield ratio and tighter chemistry limits, so it is more ductile.
Yes - its minimum yield strength is 550 N/mm2 against 500. Whether to use it is a design decision for your structural engineer.
Most house designs in India specify Fe 500 or Fe 500D. Use the grade on your structural drawings.
Only with the structural engineer's approval. A different grade changes the design assumptions, including laps and bending.
Check the grade and BIS mark rolled on the bar, match heat numbers with the mill test certificate, and test samples in an accredited lab for large orders.
Last updated 8 October 2026.
