The water quenching process produces a high-strength bar from inexpensive, low carbon steel. In the process, the surface layer of the bar is quenched with water, which pressurizes the crystal structure of intermediary layers and deforms them, while simultaneously tempering the quenched layers using the heat from the bar’s core.
Steel billets of 130 mm, also known as “pencil ingots”, are heated to a temperature of approximately 1200° C to 1250° C in a reheat furnace. They are then progressively rolled to reduce the size of the billets to the desired shape and size of the reinforcing bar. After rolling, the billets move through a quench box where the billet’s surface layer gets converted to martensite, causing it to shrink. This shrinkage pressurizes the core, helping to form the correct crystal structures, maintaining the core’s heat and austenite. A microprocessor helps in maintaining the temperature difference throughout the cross-section of the bars to ensure that they have the necessary mechanical properties during all the processes.
The bar leaves the quench box with a temperature gradient through its cross-section. As the bar cools, heat flows from the bar’s center to its surface so that the bar’s heat and pressure appropriately temper an intermediate ring of martensite and bainite.
Finally, the slow cooling after quenching automatically tempers the austenitic core to ferrite and pearlite on the cooling bed.
These bars exhibit a variation in microstructure in their cross-section and have strong, tough, tempered martensite in the surface layer of the bar, an intermediate layer of martensite and bainite, and a refined, tough, and ductile ferrite and pearlite core.
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