Processing of Raw Material
The raw material is viz. Iron ore, coal/coke, as well as the fluxes, (limestone/dolomite), are all sourced from their respective sites and stacked, recycled, and blended to the desired proportion. PMPL was the first company to manufacture corrosion-resistant steel CRS bars in South India.
Beneficiation of Coke, Agglomeration and Conversion to Coke to Columbine
Iron ore is treated to increase its iron content. The iron ore fines are then agglomerated to form pellets. To improve productivity, sinter is used. For later use, the coal is transformed into coke.
Iron making
Coke, ore, sinter, and limestone are all fed into the blast-furnace’s top. Through nozzles at the furnace’s bottom, hot air is injected. This reduces iron ore. The iron in the ore and sinter are melted to create a pool or molten steel in the furnace’s bottom. The limestone reacts with impurities, molten rock from iron ore and/or sinter, creating a liquid “slag” that floats on top.
2 – Conversions of molten steel to steel and continuous cast
Pretreatment and primary Steelmaking
Pre treatment is performed on the molten iron before it is turned into steel. The BOF contains the molten steel from the blast furnace and is filled with oxygen. This oxygen reacts with the carbon in the iron, and the carbon is eliminated as carbon dioxide.
Secondary Steelmaking
Ladle heating is then used to refine the steel’s chemical composition. This is done using a Ladle Heating Furnace or LHF and a RH De-gasifier.
Continuous Casting
Continuous casting is where the molten steel is poured into a casting device to create billets. The cross section of the billets is 165mm2.
3 – Hot rolling and thermomechanical treatment
Quenching
A hot-rolled bar is removed from the final mill stand. This includes roughing mills and intermediate mills as well as finishing mills. The rebar is instantly quenched 9 (a heat treatment in which the rebars can be rapidly cooled to achieve certain material properties). This is done using a water spray system inside the quenching box. This is done to harden and strengthen the surface, but the core will remain hot and soft.
Self-tempering
Because the core is at a much higher temperature, heat continues to be supplied to the surface even after the quenching box has been closed. This causes the outer martensitic layer to temper into a structure called Tempered Martensite . This stage is also where the core is austenitic, a typical cubical crystal structure.
Atmospheric cool
After self-tempering the bars are exposed to atmospheric cooling at room temperature on special cooling beds. The austenitic inner core transforms into a ductile, ferrite-pearlite structural. The end result is a perfect combination a strong outer (tempered martensite), and a core (ferrite) that has been heated treated.
