The steel making plant is one of the 5 production areas in Esfahan's Mobarakeh Steel Company. This plant is responsible for the production of steel slabs needed by the hot-rolling mill with the quantity and quality agreed upon with the area. It consists of the following units:
2.Electric arc furnaces (EAF’s)
3.Ladle furnace treatment (secondary metallurgy) and ladle service
4.Continuous slab casting
5.Slab cooling and conditioning
Material handling unit
This unit is responsible for the transportation, unloading, loading preparation, accumulating and distributing all raw materials and additives needed by the steel making process to be charged into the electric arc furnaces and secondary metallurgical facilities in accordance with the predetermined technical specifications
Major activities of the area:
1.Receiving and storing of the materials
2.Loading the materials in the silos for consumption in the electric arc furnaces
3.Transferring and distributing the materials needed by the electric arc furnaces and secondary metallurgical facilities.
4.Recycling of the steel wastage and preparing the scraps
5.Monitoring the direct purchase contracts
A.Delivering and distributing the materials received on conveyers from the iron making plant in order to make them available and ensure the continuation of the production process of sponge iron and additives such as lime, dolomite and so forth and transferring them on conveyor belts to the steel making plant and storing them in the electric arc furnace silos. This unit is also responsible for the controlling and scheduling the charging operations on conveyor belts and performing emergency operations on the relevant equipment.
B.Distributing the additives and consumables in accordance with storing systems of receiving, storing and distributing of about 24 materials in various tonnages, shapes and sizes into different parts of the steel making plant also takes place by this section.
Steel scraps made ready for consumption is carried to the steel scrap pools of the area and stored in the 17 pools made for this purpose with the approximate capacity of 45,000 tons. Then the scraps are loaded in loading baskets and carried on trucks into the plant for charging into the electric arc furnaces.
Electric arc furnaces unit
This unit consists of 8 electric arc furnaces with each with the capacity of 180 ton liquid steel in each heat with the transformer power of 90 MVA.
The scrap loaded in the basket by the existing overhead cranes existing in this unit is charged into the electric arc furnace and the roof of the furnace is shut and the heating operation begins. In this stage, the scrap is molten. This stage of operation is called boring. Then the sponge iron is charged into the furnace from the silos storing sponge iron. The amount of the scrap charged per heat is 170 ton. The rate of charging sponge iron is 500 – 3200 kg per minute depending on the liquid steel conditions. This stage is called melting during which the following activities take place simultaneously.
2.Graphite powder blowing
3.Charging lime and dolomite for the production of bulky slag
4.Sampling and measuring the temperature
After the sponge iron is completely molten, the refining stage befalls and final adjustments in temperature and analysis are carried out depending on the test results of the laboratory.
The slag is discharged as soon as it is needed. The final stage in the electric arc furnace operation is the tapping (discharging) stage in which the empty ladle which has been preheated according to the production procedures is directed towards the furnace and necessary amount of ferroalloys and additives such as bauxite and lime are added to the ladle simultaneous with the tapping of the liquid steel from the electric arc furnace into the ladle. The liquid steel is developed in the liquid steel containing ladle.
The total period of the heat from the tapping of the previous liquid steel to the tapping of the next liquid steel is about 150 minutes and these activities take place regularly in this unit.
Ladle furnace unit
This unit consists of 4 ladle furnaces each with the transformer power of 30 MVA and 6 bins with the capacity of 9 cubic meters in which materials such as high-carbon, mid-carbon ferromanganese, ferrosilicon, lime and calcium aluminate are stored.
The most important activities that take place in each heat on the ladle furnaces (L.F.) are as follows:
3.Adjusting chemical analysis
4.Adjusting the temperature and the time of delivery to the next unit (continuous casting unit)
5.Purification or elimination of the existing impurities
Deoxygenizing takes place for the elimination of the oxygen from the liquid steel after measuring the oxygen content of the liquid steel. After the elimination of the oxygen content some aluminum is added to the liquid steel.
Slag making takes place with the following goals:
1.Increasing the heat efficiency of the electric arc
2.Absorption of the liquid steel impurities by the to the slag
4.Reduction of the refractory lining of the slag line of the ladle
5.Prevention of re-oxidation of the aluminum dissolved in the liquid steel
6.Increasing the efficiency and easier adjustment of the chemical analysis of the liquid steel
7.Clean ladle after tapping the bottom of the ladle
8.Reduce the sound pollution
Adjusting the chemical analysis of the liquid steel:
After completing the procedures mentioned above, and sampling the liquid steel, materials needed are added to the liquid steel after calculations.
Adjusting the heat and time of delivery to the continuous casting unit:
The temperature of the liquid steel upon exist from the ladle furnace is calculated on the basis of the solidification temperature of the grade of the steel being produced and informed to the operator who must consider the tapping voltage tolerance, type of materials added to the liquid steel, amount and status of the ladle slag, method of argon blowing into the ladle and so forth, and take the liquid steel carrying ladle out in the due course which is usually about 20 minutes before the commencement of the casting operations.
Liquid steel purification
One of the responsibilities of the secondary metallurgical unit is to eliminate the impurities as much as possible. Impurities fall into the following categories:
1.Oxide impurities such as Al2O3, SiO2, MgO
2.Carbide, nitride and sulfide impurities
3.Non-metallic impurities or excessive alloy elements content of the liquid steel
4.Sulfur and phosphorus
5.Harmful gases such as hydrogen, nitrogen and oxygen
Continuous casting unit
This unit is responsible for the transformation of the liquid steel into slabs with the standard quality and dimensions as ordered by the customer and delivering it to the slab cooling and conditioning unit. This unit has four two-strand liquid steel lines of arc type with the radius of 10.5 meters. The dimensional features of the slabs are as follows:
Width: 650 – 1880 millimeters
Length: long slabs: 9.50 – 10 meters and short slabs: 4.5 – 4.75 meters
Thickness: 200 millimeters
After the determination of the temperature and chemical analysis of the liquid steel in the secondary metallurgical unit, overhead cranes move the liquid steel containing ladle to the continuous casting unit. Each heat has a 6-digit code that communicates heat details such as chemical analysis, temperature, duration, quality and so forth and the heat is traceable in the MIS system. In the continuous casting unit, the liquid steel carrying ladle is put first on the turret, and as soon as the hydraulic cylinder is attached to the sliding gate of the ladle, and the adjustment of the tundish car on the casting lines, a flow of liquid steel starts from the ladle into the tundish with the opening of the sliding gate. The flow of the liquid steel from tundish to the dies starts as soon as the stopper is opened. There is a short pause in the dies for the formation of the initial shell before the continuous casting operation commences. The freezing front starts forming inside the slab as soon as the slab leaves the die and the slab passes through rolls while being sprayed with water, and the solidification in the cross-section of the slab is completed as soon as the slabs attains the due metallurgical length. The slab is cut in the slab cutting section with due consideration of minimal wastage. The slab is engraved with a 9-digit number for identification and traceability purposes as soon as it leaves the cutting machine.
With the completion of the first stage of casting, the second stage of casting starts when the second ladle of liquid steel is placed on the other arm of the turret, and the ladle sliding gate opens for the continuous flow of the liquid steel and maintenance of the continuity of the casting process. The successive heats on average transform five heats in one single phase of the operation into slabs and the slabs thus produced and conditioned go to the next unit.
Slab conditioning and cooling unit
This unit cools down the slab in the following two ways with due consideration of the type of the slab. 1.Cooling in air
2.Cooling in water
Slabs that require air cooling move to the relevant section on overhead cranes and move to slab conditioning section after 72 hours.
Slabs that require water cooling move to two cooling tanks on the roller tables automatically and get out after 20 minutes and move to the slab conditioning section.
In the slab conditioning section, the slabs are inspected by quality control inspectors and have their surface defects identified. Then scarfing operators begin to eliminate these defects by hand-held torches. After final approval of the quality control department, the slabs move to the hot-rolling mill, but in case of non-conformity, the slabs are kept in the storehouse for later transfer to the hot rolling mill..