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QST Rebars

Reinforcement Steel Rebars

SURYADEV QST (Quenching and Self Tempering) rebars are manufactured with Technical Collaboration with Hennigsdorfer Stahl Engineering GmbH Germany, who has supplied their THERMEX cooling Technology in over 100 steel plants all over the world including SAIL.

Reheating Process

Reheating process begins with the Billets up to the re-crystallization temperature (1150° C). The re-crystallization temperature is very important because at this temperature the rolling process can be started effectively without destroying the bonding. The fuel used for reheating is producer gas. Producer gas is obtained by gasification of solid fuels like coal or biomass in the falsifier. Reheating with the use of producer gas is very Eco friendly and ensures uniform temperature of Billet from one end to other. Billets are pushed into reheating furnace with help of pusher and then heated to temperature 0f 1150° C.

Rolling Process

Once the billets reach the desired rolling temperature, they are brought outside the furnace. With the help of rolling conveyor, these billets are made to pass through the first stand i.e. Roughing Mill. With this, the process of gradual size reduction of billets begins. Following roughing mill, the size is further reduced in Intermediate and Finishing Mill. This gradual reduction is an important factor to ensure finer grain structure of the bar. The rolling continues till the required size is obtained. With help of Roller bearings fitted on the Roll Neck any unnecessary deformation of the bar is prevented. The loop scanner in the flow of the bar ensures perfectly tension less rolling process that ensures perfect round shape of the bars. The surface characteristics are finalised in this section.

Quenching Process (THERMEX)

In order to import strength to deformed mild Steel bars that have a natural strength of 250-300N/mm2, 'Controlled Quenching Process' is performed. The bar after leaving the last rolling mill stand is fed to quenching box at a very high speed. In this section, a rapid and controlled water quenching is performed reducing the temperature of surface drastically from 950° C to 300° C. Due to higher speed, only outer portion of bar (case) gets quenched while the inner part (core) remains hot. The cast due to rapid quenching gets converted in martensite form. The micro-structure is fine-grained ferrite - pearlite structure at the core and martensite case. Then the bar is cut with automatic Flying Shear and fed to the cooling bed. This is a patented technology of "Thermex".

Self Tempering & Normalizing Process

At cooling bed, the core that is still hot transfers heat outside to the case thereby tempering it. Due to this self tempering, the martensite case becomes tempered martensite site which has more strength and very high corrosion resistence properties. Quenching as well as self tempering lead to typical micro-structure of QST bar, i.e. fine grained Ferrite-Pearlite structure at the core (Soft) and tempered martensite case (Hard).

Subsequently, normalizing process starts where the bar cools down in atmospheric temperature and gradually attaining the atmospheric temperature.

Cutting

On receiving customer orders, C&B section cuts desired sizes bars as per structural design specifications. This operation is backed with complete Imported technology & equipment.

Storage & Dispatch Process

Once the bars are cooled, the steel rods are stored in finishing goods yard according to their Grades, Sizes, Lot No. or any other distinguishing factor. The material is now ready for dispatch.

Higher Strength

Suryadev QST Rebars have higher strength and are available in all grades. So, now you can have high strength rebars and thus can easily cut overall cost by optimizing consumption.

Bending Properties

Suryadev QST Rebars have excellent bend properties due to the unique ductility (elongation values) obtained by employing the German "Thermex" Technology.

Corrosion Resistance

Controlled water cooling prevents the formation of coarse carbides, which has been cited as the main cause for the corrosion prone nature of common bars. Another reason for better corrosion resistance is the absence of surface stresses caused by the cold twisting and Torsteel process.

Cost-effective

Suryadev QST Rebars require 15-30% less usage than ordinary bars for same work. This results in overall saving of 10-20%.

Better Metallurgical Properties:

Perfect temperature control system to ensure better metallurgical properties.

Perfect Roundness

Tensionless rolling through the loop scanner system during rolling process ensures reduction of oval shapes, which is generally present in traditional rolling mills. The automatic system ensures consistent, uniform properties and precise round shapes.

Precise gauge

Control systems ensure precise accurate weight of the bars by controlling gauge of the bars automatically between stringent tolerance.

Customised product

Chemical metallurgical and physical properties as per design requirements of clients are given by Suryadev. Additional relevant services are offered as per specific customer requirement.

Finer Grain structure

Size reduction from billet to the bars is done gradually in multiple stages for better and consistent grain structure. Refined and finer grain structure gives better metallurgical properties to the bars for longer life.

Higher Bonding Strength

Suryadev QST Rebars with their uniform and precise rib pattern ensure better bonding strength with concrete. This gives higher strength to the structure and hence a longer life.

Better weldability

Suryadev QST rebars bars with carbon content less than 0.25% can be used at all weld joints, without reduction in strength at the joints.

Fire Resistance

Suryadev QST Rebars have higher thermal stability. They are the preferred choice in case of elevated temperatures of 400 - 600 degrees centigrade applications (chimneys, fires).

Formability

Due to very high elongation values and consistent properties throughout the length of rebar, Suryadev QST Rebars have excellent workability and bendability.

Strain Ageing

Due to unique, scientific manufacturing process and chemical composition, Suryadev QST Rebars show no tendency of brittleness either during welding or cold deformation of welded joints.