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Carbon Structural Steel Production Technology
The production of carbon structural steel uses a wide variety of raw materials and technologies, from the traditional blast furnace route to modern electric-arc and oxygen furnaces. Each route has its own distinctive characteristics and advantages, which are explained in this article.
Blast Furnace Route
The blast furnace route to the production of carbon structural steel redirects the hottest element of the steelmaking process, the oxidation of scrap and other raw materials, away from the steelmaking vessel and into the blast furnace. Molten iron from the blast furnace is then transferred to the steelmaking vessel, where additional scrap steel is introduced and, together with the purified iron, subjected to the oxygen lancing process.
In the steelmaking process, oxygen is injected into the bath of molten iron. This causes a reaction that releases heat and generates a slag by-product. Scrap and mill scale is then added to the bath to give the desired carbon content. Additional oxidizing and reducing agents are injected into the steel bath to control slag formation and also to control the rate of cooling and, hence, the structure and properties of the steel. The goal is aimed to have a predefined rate of cooling, so that the desired carbon-equivalent composition and properties can be achieved in the end product. The level of alloying elements is also carefully controlled and can be adjusted according to the type of product to be made. The finished product is then poured into ladles or teeming vessels, which are either allowed to cool slowly or sprayed with water to accelerate cooling.
Electric Arc Furnace Route
The electric arc furnace (EAF) route to the production of carbon structural steel is focused on the efficient melting of scrap steel. The reaction between the electrodes, together with the oxygen injected into the metal bath, create a slag by-product. The main purpose of the EAF is to efficiently melt scrap steel and to achieve rapid tapping from the furnace.
Additional alloying elements and oxidizing agents are injected into the molten bath to achieve the desired carbon-equivalent composition and the desired structure and properties of the steel. During slag formation and oxidation of high-carbon scrap, a large number of micro-alloying elements is also introduced into the bath, which helps to achieve the desired characteristics of the steel.
The level of alloying elements can be varied with different types of steel. The EAF process permits the use of a variety of raw materials, such as direct-reduced iron, typically in the form of hot briquetted iron, which eliminates the need for the blast furnace route. The tapout conditions of the molten steel are also designed to ensure efficient cooling and to achieve ideal structural and microstructural characteristics. The finished product is then transferred to ladles or teeming vessels and cooled by spraying with water.
Oxygen Furnace Route
The oxygen furnace route to the production of carbon structural steel is similar to the EAF process, but the steelmaking furnace is replaced by an oxygen furnace. This approach takes advantage of the higher thermal efficiency of the oxygen furnace, which is used to melt the scrap steel and quickly achieve the desired composition with less energy input.
The oxygen lancing process is then used to produce the required amount of oxygen for the oxidation of the scrap steel, as well as to inject additional oxidizing and alloying elements into the steel bath. This method produces steel with a uniform composition and the desired properties. The tapout conditions are carefully designed to ensure efficient cooling and to achieve the ideal structural and microstructural characteristics. The finished product is then poured into ladles or teeming vessels and cooled by spraying with water.
Conclusion
Carbon structural steel can be produced using either the traditional blast furnace route, the electric arc furnace route or the oxygen furnace route. Each approach has its own advantages and applications, but all three routes use similar process steps: melting scrap steel, introducing oxidizing and alloying elements, controlling slag formation and cooling to achieve the desired properties. The steel produced in each of these routes has its own characteristic properties and can be tailored to suit particular applications.
