Steel sheet that has been wound. A slab, once rolled in a hot-strip mill, is more than one-quarter mile long; coils are the most efficient way to store and transport sheet steel. Coke The basic fuel consumed in blast furnaces in the smelting of iron. Coke is a processed form of coal. About 1,000 pounds of coke are needed to process a ton of pig iron, an amount which represents more than 50% of an integrated steel mill's total energy use. Metallurgical coal burns sporadically and reduces into a sticky mass. Processed coke, however, burns steadily inside and out and is not crushed by the weight of the iron ore in the blast furnace. Inside the narrow confines of the coke oven, coal is heated without oxygen for 18 hours to drive off gases and impurities.