Steelmaking is the process for producing steel from iron and ferrous scrap.
In steelmaking, impurities such as nitrogen, silicon, phosphorus,sulfur and excess carbon
are removed from the raw iron, and alloying elements such as manganese, nickel, chromium
and vanadium are added to produce different grades of steel.
Limiting dissolved gases such as nitrogen and oxygen, and entrained impurities in the
steel is also important to ensure the quality of the products cast from the liquid steel.
There are two major processes for making steel, namely basic oxygen steelmaking which has
liquid pig-iron from the blast furnace and scrap steel as the main feed materials, and
electric arc furnace steelmaking which uses scrap steel or direct reduced iron as the
main feed materials.
Oxygen steelmaking is fuelled predominantly by the exothermic nature of the reactions
inside the vessel where as in EAF steelmaking, electrical energy is used to melt the solid
scrap and/or DRI materials.
In recent times, EAF steelmaking technology has evolved closer to oxygen steelmaking as
more chemical energy is introduced into the process.
History
Steelmaking has played a crucial role in the development of modern technological societies.
Cast iron is a hard brittle material that is difficult to work, whereas steel is malleable,
relatively easily formed and a versatile material.
For much of human history, steel has only been made in small quantities.
Since the invention of the Bessemer process in the 19th century and subsequent technological
developments in injection technology and process control, mass production of steel has become
an integral part of the world's economy and a key indicator of technological development.
The earliest means of producing steel was in a bloomery.
Early modern methods of producing steel were often labour-intensive and highly skilled
arts.
See: finery forge, in which the German finery process
could be managed to produce steel.
blister steel and crucible steel.
An important aspect of the industrial revolution was the development of large-scale methods
of producing forgeable metal.
The puddling furnace was initially a means of producing wrought iron, but was later applied
to steel production.
The real revolution in steelmaking only began at the end of the 1850s when the Bessemer
process became the first successful method of steelmaking in quantity, followed by the
open-hearth furnace.
Modern processes Modern steelmaking processes can be broken
into two categories: primary and secondary steelmaking.
Primary steelmaking involves converting liquid iron from a blast furnace and steel scrap
into steel via basic oxygen steelmaking or melting scrap steel and/or direct reduced
iron in an electric arc furnace.
Secondary steelmaking involves refining of the crude steel before casting and the various
operations are normally carried out in ladles.
In secondary metallurgy, alloying agents are added, dissolved gases in the steel are lowered,
inclusions are removed or altered chemically to ensure that high-quality steel is produced
after casting.
Primary steelmaking
Basic oxygen steelmaking is a method of primary steelmaking in which carbon-rich molten pig
iron is made into steel.
Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes
it into steel.
The process is known as basic due to the chemical nature of the refractories—calcium oxide
and magnesium oxide—that line the vessel to withstand the high temperature and corrosive
nature of the molten metal and slag in the vessel.
The slag chemistry of the process is also controlled to ensure that impurities such
as silicon and phosphorus are removed from the metal.
The process was developed in 1948 by Robert Durrer and commercialized in 1952–53 by
Austrian VOEST and ÖAMG.
The LD converter, named after the Austrian towns of Linz and Donawitz is a refined version
of the Bessemer converter where blowing of air is replaced with blowing oxygen.
It reduced capital cost of the plants, time of smelting, and increased labor productivity.
Between 1920 and 2000, labour requirements in the industry decreased by a factor of 1,000,
from more than 3 worker-hours per tonne to just 0.003.
The vast majority of steel manufactured in the world is produced using the basic oxygen
furnace; in 2011, it accounted for 70% of global steel output.
Modern furnaces will take a charge of iron of up to 350 tons and convert it into steel
in less than 40 minutes, compared to 10–12 hours in an open hearth furnace.
Electric arc furnace steelmaking is the manufacture of steel from scrap or direct reduced iron
melted by electric arcs.
In an electric arc furnace, a batch of steel may be started by loading scrap or direct
reduced iron into the furnace, sometimes with a "hot heel".
Gas burners may be used to assist with the melt down of the scrap pile in the furnace.
As in basic oxygen steelmaking, fluxes are also added to protect the lining of the vessel
and help improve the removal of impurities.
Electric arc furnace steelmaking typically uses furnaces of capacity around 100 tonnes
that produce steel every 40 to 50 minutes for further processing.
By-product gases from the steel making process can be used to generate electricity through
the use of reciprocating gas engines.
Secondary steelmaking Secondary steelmaking is most commonly performed
in ladles and often referred to as ladle.
Some of the operations performed in ladles include de-oxidation, vacuum degassing, alloy
addition, inclusion removal, inclusion chemistry modification, de-sulphurisation and homogenisation.
It is now common to perform ladle metallurgical operations in gas stirred ladles with electric
arc heating in the lid of the furnace.
Tight control of ladle metallurgy is associated with producing high grades of steel in which
the tolerances in chemistry and consistency are narrow.
HIsarna steelmaking
The HIsarna steelmaking process is a process for primary steelmaking in which iron ore
is processed almost directly into steel.
The process is based around a new type of blast furnace called a Cyclone Converter Furnace,
which makes it possible to skip the process of manufacturing pig iron pellets that is
necessary for the basic oxygen steelmaking process.
Without the necessity for this preparatory step the HIsarna process is more energy-efficient
and has a lower carbon footprint than traditional steelmaking processes.
See also History of the steel industry
History of the steel industry Argon oxygen decarburization
Decarburization FINEX
Flodin process Steel mill
Carbon Additive References
External links The short film The Drama of Steel is available
for free download at the Internet Archive [more]
U.S. Steel Gary Works Photograph Collection, 1906-1971
"Steel For The Tools For Victory" , December 1943, Popular Science large detailed article
with numerous illustrations and cutaways on the modern basics of making steel