QUENCHING
In the first stage, quenching starts with the hot rolled bar leaving the final stand and immediately being quenched by a special high Pressure Water spraying System. The process results in formation of "Martensite" on the outer surface of the bar while the core remains austenitic.
SELF-TEMPERING
In the second stage the bar leaves the water quenching box and is exposed to air. The heat flux from the still hot core reheats the outer surface of the bar. The Martensite formed in the first stage is thus subject to self-tempering giving a structure called "Tempered Martensite" which is strong and tough. The core is still austenitic at this stage.
ATMOSPHERIC COOLING
The third and final stage of "Atmospheric Cooling" takes place on the cooling bed, where the austenitic core is transformed into the ferrite pearlite ductile core. The final structure, thus, consists of a combination of the strong outer layer of tempered martensite and a ductile core of ferrite-pearlite.