Ceylon Steel Corporation Ltd., as the pioneer steel manufacturer in Sri Lanka, once again, keeping up to its pioneering spirit, introduced the high strength, high workable reinforced steel bar to Sri Lanka â€“ Quench and Self Tempered Re-Bars or QT Bars for short.Until the introduction of Lanwa QT Bars, steel manufactured in Sri Lanka were of the type called â€˜Hot-rolled and Cold- workedâ€™ steel. Lanwa was a pioneer in introducing that type of steel, under the brand name â€˜Torâ€™, back in the nineteen Â eighties.
But when the world progressively abandoned â€˜cold-workedâ€™ re-bars, and, found a superior replacement in â€˜Quenched and Self-tempered Steel, Lanwa was the first to introduce that superior manufacturing process, too, to Sri Lanka
The process involved an entire re-hauling of the manufacturing plant. For it no longer relied on the labour intensive, time consuming, costly procedure of manually cold-twisting the rebar for strength. Instead it employed and entirely a different method.
Â Manufacture of Lanwa QT BarsÂ Â
Lanwa purchases only the finest quality billets from overseas manufacturers withÂ a reputation for producing the purity needed for the manufacture of quench and self-tempered steel re-bars.
In spite of the quality assurance from reputed billet manufacturers, Lanwa utilizes their very own ultra â€“modern laboratory to do their own verification and testing. Each batch of imported billets are sampled and tested for 32 metal and nonmetal components employing anÂ Ultra Modern LaboratoryÂ spectro meter.
Unlike most re-bar manufacturing plants, who uses a single zone re-heating furnace, Lanwaâ€™s reheating furnace has four â€“firing zones. This guarantees the 12 foot, 530 kilo gram mass of the entire billet is brought to a uniform temperature of 1200C. Another vital parameter necessary to maintain the desired mechanical properties of the finished product.
It is paramount that the hot-rolling reduction process, from billets to the desired profile of the re-bars, be taken in stages to assure the right consistency of micro-structural and mechanical properties of the finished product. With a focus on quality and standards, Lanwa is the only steel manufacturer equipped with an 18 multi-pass stand, hot-rolling mill in Sri Lanka.
The re-bar leaving the last stand of the hot-rolling mill, then,Â passes through a special water cooling section. The cooling efficiency of this installation is such that the surface layer of the bar is quenched into martensite, with the core remaining austenitic. From this fabrication process, the metallographic structure of the core turns out to be different from that of the skin.
When the bar leaves the severe cooling section, the temperature gradient established in its cross- sectionÂ causes the heat to flow from the centre to the surface. This increase in the temperature of the surface layer results in the self-tempering of the martensite. Finally, during the slow cooling of the rebar on the cooling bed, the austenitic core transform into ferrite and pearlite, or into bainite, ferrite and pearlite.
This type of steel exhibits a stress-strain diagram with a yielding plateau like hot-rolled steel. It also presents excellent weldability, bendability and ductility characteristics.