JNTU B.Tech III STEEL MAKING Previous Question Paper (November/December - 2020 - R16)

The fundamental Principle of Steel Making is the controlled oxidation of impurities present in the molten pig iron (hot metal) or scrap. Pig iron produced in a blast furnace contains high levels of carbon (3.5–4.5%), silicon, manganese, phosphorus, and sulfur. The steelmaking process involves oxidizing these elements to specific levels required for the desired grade of steel. Carbon is removed as carbon monoxide or dioxide gas, while silicon, manganese, and phosphorus are oxidized to form a liquid slag, typically using lime as a flux to neutralize acidic oxides.

The chemical reactions generally follow the order of oxidation based on oxygen affinity: Silicon and Manganese are oxidized first, followed by Phosphorus (which requires basic conditions and lower temperatures), and finally Carbon. The process is represented by the general reaction:

The two primary industrial routes for steelmaking are the Integrated Route and the Electric Arc Furnace (EAF) Route:

• Integrated Route (BF-BOF): Raw materials (Iron ore, Coke, Limestone) are processed in a Blast Furnace (BF) to produce liquid hot metal. This hot metal is then refined in a Basic Oxygen Furnace (BOF) where high-pressure oxygen is blown to reduce carbon and impurities.
• EAF Route: This route primarily uses steel scrap or Direct Reduced Iron (DRI) as the metallic charge. Electrical energy is used to melt the charge, and oxygen lancing is employed for refining.

Both routes converge at the Secondary Steelmaking stage, where precise alloying, deoxidation, and temperature control are performed, followed by Continuous Casting to produce semi-finished shapes like billets, blooms, or slabs.