In this process wrought iron bars are introduced in a furnace in between powdered charcoal layers and are subjected to a very high temperature – about 7000 Celsius for about a week to fortnight depending upon the required quality of the steel. The conditions slowly diffuse carbon into iron and cause the carbon to become dissolved in the iron, raising the carbon percentage. Steel obtained from this process is called “blister steel” due to the blister-like marks formed on the surface due to the evolved gases during the manufacturing process. The carbon amount here is usually around 0.75% to 1.5%.
The process involves heating of either blister steel fragments or short lengths of wrought iron bars mixed with charcoal inside fire clay crucibles. The resulting molten steel is allowed to run through iron moulds. Such steel is called “cast iron.” Cast steel is extremely hard and perfectly homogenous. These are specifically used for making cutting tools and the finest cutlery items.
In this process pig iron is melted in a cupola and poured into Bessemer converter which is pear shaped and has a steel shell lined with refractory material. It’s pivoted on trunnions so as to facilitate tilting, pouring or charging.
Once the above converter is charged with molten pig iron, a strong thrust of air is blasted across the molten mass for about 20 minutes through nozzles provided at the bottom of the vessel. The process oxidizes all traces of the carbon and silicon present, leaving the converter with pure iron.
After this, the blasting of air is stopped and the specified amount of ferro-manganese is added to it for the sake of including the recommended content of carbon and manganese to the steel.
The air blasted procedure is again initiated for some time, ensuring perfect mixing of the alloy.
The converter is then tilted so that the molten material can be discharged into the ladles. In the final step, the molten alloy is shifted into rectangular moulds where it’s obtained in the form of solid ingots.