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Processes - Ferrous (Iron / Steel): Iron Making

Iron
Molten iron is produced by the blast furnace, by the EAF furnace, or by a number of alternative processes (both batch and continuous) that are in various stages of development. Regardless of the method to produce iron, it is then refined into usable grades of steel (carbon, alloy, or stainless).

Steel
Iron is refined into steel, fed from the blast furnace into the BOF, directly in an EAF, or in a ladle refining station downstream of the EAF.

Worldwide over 20 iron making and direct steel making technology scenarios are being evaluated and are in various forms of development. Today in the U.S. and North America, the iron intended for refinement into steel is produced by two primary methods. The BOF (fed by the Blast Furnace) and the EAF (an electric, mainly scrap based method) are utilized to process virtually all the primary steel in the U.S.A. A timeline showing the demise of the Open Hearth method and the corresponding rise of both the BOF and EAF methods over the past nearly 40 years is shown on the following page.

The very latest production statistics, released by the American Iron & Steel Institute, illustrate the continuing and accelerating trend to complete steel making in EAFs.

Blast Furnace Trends and Process Information
Overall, the number of blast furnaces is decreasing. However, the productivity of the average blast furnace is increasing. The productivity rise is due to a number of factors including the steel industry effort to inject supplemental fuels in order to reduce coke consumption and provide cost savings. The chart below shows the trend toward fewer, more productive facilities.

The purpose of a blast furnace is to separate iron from iron ore and in the process produce molten iron (for further steel making processes). The output of a blast furnace is transported (usually by insulated railroad cars called Torpedo Cars) to the BOFshop for refinement into steel.

EAF Furnace Trends and Process Information
Overall, the use of EAF furnaces is increasing. The range of electric arc technologies is expanding (DC, high impedance AC-EAF, etc.). And a number of approaches are being implemented in order to improve productivity, reduce or minimize electrode consumption or breakage, and expand the range of steel grades that can be produced in an EAF shop.

Approximately 225 EAF furnaces are operated by 90 companies in the USA.

EAFs traditionally produce lesser tonnage of lower grade products (rebar, other rod wire materials, etc.). This is due to two primary, quality-related issues. Historically, EAFs could not produce steel grades that were low in nitrogen content. This is because atmosphere dissociation near the high temperature electric arc leads to nitrogen pick-up in the molten metal "bath". Also the content of "residuals" cannot be precisely controlled. These two items have limited the grades EAFs can produce. However, the ability to produce a heat of molten metal and then, in some cases, perform secondary refining steps in an EAF is evolving.