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