Ductility is not a nice-to-have. Here is how the D-grade elongation floor changes the way a frame fails.
The rim-and-core structure
Quenching hardens only the outer 2mm of the bar. The retained core heat then tempers that rim while keeping a ferrite-pearlite centre, which is why a TMT bar can be both high-yield and bendable around a small mandrel.
What D-grade actually guarantees
The D suffix locks minimum elongation and a controlled UTS-to-yield ratio. In a seismic event that ratio decides whether a joint hinges predictably or snaps.
Detailing consequences
Higher confidence in ductility lets designers reduce congestion at beam-column joints, which improves concrete compaction and, in turn, real-world durability.