Iron & Steel Industry

Direct-reduced iron (DRI), also called sponge iron,[1] is produced from direct reduction of iron ore (in the form of lumps, pellets or fines) by a reducing gas produced from natural gas or coal. The reducing gas is a mixture majority of hydrogen (H2) and carbon monoxide (CO) which acts as reducing agent. This process of directly reducing the iron ore in solid form by reducing gases is called direct reduction. DRI is successfully manufactured in various parts of the world through either natural gas or coal-based technology. Iron ore is reduced in solid state at 800 to 1,050 °C (1,472 to 1,922 °F) either by reducing gas (H2+CO) or coal. The specific investment and operating costs of direct reduction plants are low compared to integrated steel plants and are more suitable for many developing countries where supplies of coking coal are limited. Direct-reduced iron has about the same iron content as pig iron, typically 90–94% total iron (depending on the quality of the raw ore) as opposed to about 93% for molten pig iron, so it is an excellent feedstock for the electric furnaces used by mini mills, allowing them to use lower grades of scrap for the rest of the charge or to produce higher grades of steel.

Continuous casting, also called strand casting, is the process whereby molten metal is solidified into a "semi-finished" billet, bloom, or slab for subsequent rolling in the finishing mills. Prior to the introduction of continuous casting in the 1950s, steel was poured into stationary molds to form ingots. Since then, "continuous casting" has evolved to achieve improved yield, quality, productivity and cost efficiency. It allows lower-cost production of metal sections with better quality, due to the inherently lower costs of continuous, standardised production of a product, as well as providing increased control over the process through automation. This process is used most frequently to cast steel (in terms of tonnage cast). Aluminum and copper are also continuously cast. Sir Henry Bessemer, of Bessemer converter fame, received a patent in 1857 for casting metal between two contra-rotating rollers. The basic outline of this system has recently been implemented today in the casting of steel strip.

Steel is manufactured by the chemical reduction of iron ore, using an integrated steel manufacturing process or a direct reduction process. In the conventional integrated steel manufacturing process, the iron from the blast furnace is converted to steel in a basic oxygen furnace (BOF). Steel can also be made in an electric arc furnace (EAF) from scrap steel and, in some cases, from direct reduced iron. BOF is typically used for high-tonnage production of carbon steels, while the EAF is used to produce carbon steels and low- tonnage specialty steels. An emerging technology, direct steel manufacturing, produces steel directly from iron ore. This document deals only with integrated iron and steel manufacturing; that on Mini Steel Mills addresses the electric arc steel process and steel finishing processes. Steel manufacturing and finishing processes discussed in that document are also employed in integrated steel plants. See also Coke Manufacturing. In the BOF process, coke making and iron making precede steel making; these steps are not necessary with an EAF. Pig iron is manufactured from sintered, pelletized, or lump iron ores using coke and limestone in a blast furnace. It is then fed to a BOF in molten form along with scrap metal, fluxes, alloys, and high-purity oxygen to manufacture steel. In some integrated steel mills, sintering (heating without melting) is used to agglomerate fines and so recycle iron-rich material such as mill scale.

The LMF’s function is to refine the steel chemistry and maintain temperature. The LMF also acts as a buffer or holding area between the melt shop and caster. Ladle arrival at the caster must be closely synchronized with the process. The ladle is lowered by crane onto the LMF car. The LMF is equipped with a bulk flux and alloys batching system, alloy wire feeders, H2O cooled roof and electrodes to allow temperature adjustments. Argon gas is bubbled through the ladle also to aid in refining. The LMF operator takes another sample of the steel, and based on the sample results, adds a controlled amount of lime and alloys to the steel in the ladle. Lime reacts with impurities, forming slag that floats on top of the metal. As needed, alloys are added to the steel by using the bulk alloy system, dumping bagged alloys into the ladle, and by using the wire feeder to feed metallurgical wire containing alloys. If necessary, the electrodes can be used to adjust or maintain steel temperature. When the chemistry and temperature at the LMF are within specifications, the ladle car moves by rail into a position where it is accessible to the overhead crane. The crane lifts the ladle to the caster when called for by the caster. The LMF acts as a buffer between the melt shop and the caster.