Refractories for electric arc furnace have been considered versatile equipment for the manufacturing of steel right since the very first commercial application in the year 1903. Initially, these furnaces were used to produce stainless steel – the purest form of steel – with a very high production cost. Nevertheless, with constant innovations in engineering and technology after the 2nd world war, the production cost saw a substantial decrease, and the steel production because commonplace through this methodology.
The share of electric arc furnaces has increased in the steelmaking process because of the advent and introduction of high-capacity furnaces. The availability of electricity at moderate prices has also contributed a lot to making this process popular and cost-effective. However, the conditions towards the refractories became severe with a high power-rating in the furnaces.
Truth be told, a modem electric arc furnace is having around 85% of the roof and 70% of side walls fixed with water-cooled boards. Along these lines, the particular utilization has come down significantly and has been accounted for flapping around 2 kg/ton of steel against 10- 12 kg with practically no water-cooled board. The decrease in the utilization has been made conceivable by the improvement and utilization of top-notch refractories with exact control in different properties, including design adjustment and, furthermore, by changing the cycle parameters for making them more viable with the refractories. The different specialized advancements which have helped in decreasing the headstrong utilization are as per the following:
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Introduction of E.B.T system for bringing down the thermal fluctuations
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Introduction of DC furnace in carrying off hot spots
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Introduction of LF
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Application of water-cooled panels.
Electric Arc Furnace Process at a glance
The EAF is refractory lined and loaded up with scrap and additionally other created iron units. The scrap is softened with a powerful electric circular arc from the hub/hubs making liquid metal. Excellent refractory brick is needed to endure the high temperatures decreasing heat loss to convert steel into liquid. Present-day EAF vessels are equipped with oxygen burners to forestall cold spots in the liquefying salvaged material cycle. When the dissolution is finished, it is moved into a spoon to begin the next procedure.
Refractory Lining of the Electric Arc Furnace
Refractories for the lining of the EAF rely upon its design. The working circumstances additionally impact the refractory performance. The working conditions in the electric arc furnace call for refractories that are chemically fundamental and show a high level of resistance to high temperature as well as thermal cycling. The design of the contemporary EAFs highlights the capricious base tap-opening and calls for special refractories for their lining.
A large number of design features are associated with electric arc furnaces but their grouping is done based on the following:
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Tapping design that includes bottom tapping or side tapping
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The power source that includes DC (direct current), or AC (alternating current)
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Supplementary oxygen (O2) use for an increase in the melting rate.
Wear Mechanisms at a glance
Corrosion
Corrosion is the most significant wear mechanism in electronic arc furnace refractories. It happens due to different types of chemical reactions of the metallic oxides particularly in the slag with the refractory materials. Magnesia (MgO) from the refractory lining is dissolvable in the fluid slag, with immersion levels going from 6 % to 14 %, contingent upon the FeO content. The chemical corrosion responses bring about the wearing of the lining and the result of the reactions becomes a part of the slag.
Corrosion reactions can be brought down by neutralizing FeO with fluxes and by having a control on the O2 content of the slag. It can also be reduced by saturating the slag with MgO via external means. The C in the refractory results in deoxidization of corrosive slag at the slag or refractory interface, this way minimizing lining corrosion.
Oxidation
In refractory wear by oxidation, the C of the lining is oxidized in reaction either with O2 or FeO in the slag. As the C of the lining reacts, the C content of the refractory shrinks, and the refractory strength is lost and it is washed away. The C oxidation mechanism also takes place on the cold face of the brick particularly when there are holes in the steel shell.
Melting
It is also one of the wear mechanisms for refractories in the EAF. The unshielded electric bend creates temperatures that are well over the dissolving point of numerous refractories. Dissolving is the straightforward stage change of the refractories from the solid to the fluid, and the fluid stage when framed is then washed away. Melting can prove to be a serious issue in the
electric arc furnace refractory lining particularly when it is not detected timely and not corrected with immediate attention.
Hydration
Since water is broadly being utilized in present-day EAFs, there are frequencies of water spills. Refractories are effortlessly harmed by water or steam because of the hydration of the MgO or lime items in the refractories. Hydration brings about the development of the singular grains containing the lining. These grains develop and explode, upsetting the lining.
Spalling
Refractory wear due to spalling happens when the refractory is exposed to fast heating or quick cooling. Quick heating or fast cooling cause stresses in the lining area and when these stresses surpass the innate strength of the refractory material, it results in breaking. At the point when these cracks intersect, pieces of refractory drop out of the lining. This mechanism of refractory damage is seen and observed often in the roof refractories because they are heavily exposed to cyclic heating and cooling.
Concluding Remarks
RHI Magnesita India is the leading supplier of high-grade refractory products including refractories for electric arc furnace and electric arc furnace refractory lining systems indispensable for industrial high-temperature processes exceeding 1,200°C. The company is a single refractory solutions platform offering the industry’s most comprehensive product and solutions portfolio including Magnesia and Alumina-based bricks and mixes for large industrial customers. More details can be obtained from the website of the company.