AKS TMT 500W bars are produced from the world-renowned TMT technology. TMT stands for Thermo – Mechanical Treatment. It is a specially designed heat treatment process involving quenching and tempering of steel.

Quenching is a metallurgical process involving the rapid cooling of the steel to strengthen and harden the steel. Although quenching makes the steel stronger and harder, it also makes the steel brittle. To eliminate this brittleness, the material is tempered after quenching.

The key feature of the TMT technology is that it converts a low carbon, low strength steel to low carbon but high strength steel.

Iron is a unique element. When carbon is introduced into iron it becomes steel. Steel, at different temperature, behaves differently. For instance, at very high temperatures it becomes soft and when cooled very rapidly it becomes strong and hard. This simple property of steel has been utilized in the TMT technology. Without introducing high amount of carbon into the steel, just by cooling the steel from a specific high temperature at a specific cooling rate and for certain duration, the strength of the steel is increased. The figure below shows how a water cooling system is introduced at the exit end of a rolling mill to produce TMT bars.

Stage 1- Quenching: The hot-rolled bars, at high temperature from the rolling mill, enter the water cooling system. Rapid cooling (quenching) is done in this special water system converting the surface layer of ribbed bar into hardened structure.

Stage 2- Tempering: When the bars reach the cooling bed, the surface layer of the bar is cooler while the core is hot. Due to the temperature gradient, heat flows from the core to the surface. This heat is absorbed by the surface and it softens slightly such that the surface is no longer brittle. This softening process is called tempering.

Stage 3- Air-cooling: Now both the surface and the core cool slowly down in air to room temperature. This slow cooling in air transforms the core of the bar into fine-grained ferrite-pearlite. Final microstructure of the bar is tempered martensite at the surface and fine ferrite-pearlite at the core.