Modern Steel Mills L.L.C. operates three completely operational steel manufacturing units in West Bengal. An automated integrated steel plant at Durgapur has Quality Assurance & Testing laboratories, Rolling Mill with Thermex System, Continuous Billet Casting Mill, DRI Unit, EAF, Steel Melting Shop Equipped with Electric Arc Furnace. The company has collaborated with Concast AG-Zurich and HSE Germany to set up the plant.
Best TMT Bar Manufacturing Plants India – Sponge iron is produced making use of a solid reductant involving reducing iron ore in lumps or pellets form along with a carbonaceous material like coal, in the Direct Reduced Iron (DRI) plant. There is a rotary kiln to carry out the reduction at specific temperature (8500C – 10500C). The kiln is inclined and rotates to move the raw material from its feed end to the discharge end. During this movement process, iron ore reduces. The material discharged from the kiln is cooled down by a rotary cooler and is then separated from the coal char. The basic reactions are as follows
3Fe2O3 + CO = 2Fe3O4 + CO2
Fe3O4 + CO = 3FeO + CO2
FeO + CO = Fe + CO2
Electric Arc Furnace
The summarization of the steps involved in an arc furnace is as follows:
The preparation of the Charge is as per the grades proposed chemistry for the targeted grade, Sponge iron and other ingredients together with lime in a close requisite ratio is charged in the arc furnace.
Melting is carried out by injecting electrical energy to the charge materials through three graphite electrodes. CO is produced when the injected carbon reacts with oxygen, that bubbles through the bath forming foamy slag. The excess CO reacts with oxygen and converts to carbon dioxide and again generate heat. Oxygen will react with components in the bath, that include phosphorus, sulphur, silicon and manganese. Slag is formed from the oxides. The charged material is melted at about 1800°C in arc furnace.
Once enough charge is melted and enough space is created, it’s time for the second charge. This way the process is repeated. Temperature is measured when the final charge is melted and it reaches at melt stage. Along with the temperature measurement, sample is drawn to determine the amount of oxygen to be blown during refining.
At the refining stage, undesired elements in steel, such as phosphorus and steel are reduced, and the carbon is brought down to the required levels. Easy removing of sulphur and phosphorus can be achieved in EAF, which is not possible in Induction Furnace. In the early refining stage, phosphorus is removed. Sulphur is removed during the reducing stage as sulphides in slag.
Aluminium, manganese and silicon react with oxygen before carbon to form oxides that go into the slag. The reaction of carbon with oxygen generates CO, which bubbles through the bath, cause the slag to foam and has several beneficial effects. The foaming is helpful in reducing the level of hydrogen and nitrogen in steel. At the end of refining stage, temperature is measured, and the sample is drawn for analysis.
In the de-slagging process, the slag layer above the steel is removed from the furnace. This is an important process to remove impurities from the molten material.
The furnace in order to remove slag is tilted towards the slag door. During the early heating stage when the temperature is relatively low, Phosphorus is transferred to the slag. At the beginning of refining process, the first de-slagging removes the large portion of the phosphorous (as P2O5) and thus avoids phosphorous reversal to the metal. The furnace is de-slagged many times during the refining state.
The tap holes open when the required temperature and composition are achieved, and the tapping of metal into the ladle occurs, which is then sent to continuous casting unit to cast billets. During the tapping process, bulk alloys are based on the bath analysis for the required steel grade. Before further processing, De-oxiders might be added to the steel for controlling the oxygen content. This is generally referred as killing of steel. Aluminium or silicon in the form of ferrosilicon or silicon manganese are added.
Continuous Billets Casting
Through EAF, Molten Steel is tapped into a laddle and transferred to the continuous casting machine. From the laddle, liquid steel flows into the tundish and then into water-cooled mold. In the mold, solidification begins. Based on the length needed, the continuous Billets from the CCM is sized.
Rolling Mill with Thermex Technology
The produced billets are re-heated at 1200°C in the re-heating furnace and then rolled into finished material sections in the Rolling Mill Unit. If TMT re-bard are needed to be manufactured, the re-bars are guided through specially designed Thermex pipes right from finishing stand of the rolling mill, to obtain special property.
From the finished mill stand, the hot rolled bar enters into the ‘Thermex System’ and is quickly cooled by a water spray system. As the TMT re-bar is quickly cooled, its surface hardens to a depth optimized for each section, creating a martensitic rim and the core remains hot and austenitic. Quenching is the word for the quick cooling process.
As the re-bars leave the quenching box, their core remains hot in comparison to the surface. It allows the heat to flow from the surface’s core and cause Tempering of the outer Martensite layer. It forms a structure known as ‘Tempered Martensite’.
The cooling bed allows atmospheric cooling. In this, transformation of Austenitic core into ductile Ferrite-Perlite structure is carried out. The final structure comprises stronger outer layer (Tempered Mastensite) with ductile core (Ferrite-Pearlite). The material’s tensile strength increases in this process, while high ductile and weldability are kept. The complete process is a patented technology from HSE, Germany under the brand ‘Thermex’.