Steel Making Methods

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Steel Making Methods

| Advantages| Disadvantages|
Basic Oxygen Furnaces| * Very high production rates and low residual element * Does not burn fuel| * Good efficiency requires large amount of pig iron to continue production. * Requires costly filtering process due to high levels of pollutants produced. * High refurbishing costs. * High dependence on blast furnace/coking.| Electric Arc Furnaces| * Minimal emissions/pollution. * Filtering of scrap not necessary. * Easy temperature control. * Precise alloying. * Economical to use scrap metal. * Contamination free. * Simultaneous deep deoxidising and desulfurization actions.| * Excessive electricity required. * Requires a steady supply of scrap metal * High transportation cost * Enclosures to reduce high sound levels * Dust collector for furnace off-gas * Slag production * Cooling water demand * Heavy truck traffic for scrap, materials handling, and product| The first step in the process, is to make the steel itself. The most common method of steel making, constituting for over 60% of worldwide production uses a Basic Oxygen Furnace (BOF). This process includes taking over 75% pig iron and reducing it to a low-carbon steel in an abundance of oxygen. The second type utilises Electric Arc Furnaces (EAFs). This involves melting up to 100% recycled scrap and reforming it using the heat produced from electrical arcs between highly charged electrodes. Figure 2 (right & below): EAF Process

Figure 2 (right & below): EAF Process
Figure 1 (left): BOF Process
Figure 1 (left): BOF Process

From the table above it is clear to see that without an established, effective transport system that allows for large amounts of scrap metal to be processed, the Basic Oxygen Method has fewer disadvantages. However, as TATA Steel already has an efficient system in place, the most feasible method would be using Electric Arc Furnaces. Despite initial costs, using EAFs save on energy and raw materials, making it more environmental and cost friendly in the long run. ‘Whilst a typical integrated (ie. BOF-route) steel mill today costs about $1100 per tonne of installed capacity, a medium-size EAF-route mini-mill today costs under $300 per tonne in terms of the initial capital outlay. ‘1 Casting Methods

The next stage in the process is to shape the steel and this is done by casting. Casting involves allowing molten metal to be poured into a mould to it can cool and solidify into a desired shape. The two most common methods of casting are Ingot Casting and Continuous Casting. The first of which is a traditional method that has largely been discontinued in mass production since the 1950s. It involves moulding the steel into bars (or ingots) before being reshaped and treated. Continuous casting however misses out the ingot stage and skips straight to having the metal in the form of slabs, billets or blooms for subsequent rolling in the finishing mills. Figure 4 (left): Continuous Casting Process

Figure 4 (left): Continuous Casting Process

Figure 3 (left): Ingot Casting Process
Figure 3 (left): Ingot Casting Process

Because Continuous Casting is basically an “evolved” version of Ingot Casting, there are now little or no advantages of Ingot Casting. Continuous Casting is more advantageous because:

* Reduced overall costs
* Improved quality of steel due to less variability in chemical composition both along the thickness and along the length and surface has fewer defects. * Increased yield, since it is not necessary to crop the ends of continuously cast slabs. * Reduced energy costs because the slabs are sent directly to hot rolling and do not require pits for reheating. Also, the thicknesses of continuously cast slabs are half the thickness of ingot castings and thus require lower energy for hot rolling. * Less pollution/emissions.

* More amenability over the dimensions.

Because of all this, the clearly...
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