This is a special heat treatment process, wherein the heat treatment is done from
the heat of the rolling process itself. Ingots/Billets which are heated in a re-heating furnace, are rolled
through a series of rolling stands, and progressively reduced to the final size and shape of the Rebar.
As the hot rolled Rebar emerges from the finishing stand of the Bar Mill, it is rapidly cooled. This
quenching process by a special water spray system converts the surface layer of the bar to a hardened
structure called ‘Martensite' while the core remains ‘Austenitic'
The second stage of ‘tempering' begins as the bar leaves the water cooling section.
In this stage, the heat flows from the core to the surface layer, transforming it into ‘Tempered Martensite':
while the core continues to stay ‘Austenitic'.
The third and final stage takes place on the cooling bed. Here the Austenitic core is transformed to a ductile ‘Ferrite-Pearlite' core. The finished bar has a micro structure comprising a tough outer layer of ‘Tempered Martensite' and a ductile core of ‘Ferrite - Pearlite'.
This composite structure gives excellent yield strength to the bar along with superior ductility and weld ability.
