The re-bar leaving the last stand of hot rolling passes through a special water cooling section. The cooling is such that a surface layer of the bar is quenched into martensite, the core remaining austenitic. The quenching treatment is stopped when a determined thickness of martensite has been formed under the skin. The re-bar leaves the drastic cooling section, the temperature gradient established in its cross section causes heat to flow from the centre to the surface. This results in self tempering of martensite. Finally, during the slow cooling of the re-bar on the cooling bed, austentic core transforms into ferrite and pearlite.
       Peekay TMT is produced by the world's most advanced technology licensed from Centre de Recherches Metallurgiques (CRM), Belguim, inventors of this process. Tempcore bars are being successfully used in most parts of the developed world. TMT are produced in two grades:  TMT 415 and TMT 500. The numbers indicate the proof stress. Because of the unique manufacturing process, TMT bars exhibit an excellent combination of strength and ductility that far exceeds the minimum limits specified by IS:1786. Typical values for yield strength are as high as 465 N/mm2 for TMT (as against IS standards, 415 N/mm2). Ductility as measured by elongation is 21% min (as against standards 14.5% min). Thus, you get product which offers you higher safety margins.