Tuesday, April 17, 2012

How to make Steel

Allegheny-Ludlum steel furnace in action. wikimedia

Iron making is strictly divine business and is done in the heavens in enormously powerful furnaces, using nuclear processes inside supergiant stars.

Steel making is a human business that is made possible by inventions of the almost divine spirit God has breathed into us. It takes lots of energy, heat and furnaces, spectacular glows of red and yellow flames and molten materials... somewhat resembling iron making.

Luckily, steel making is not quite as demanding on resources and energy as iron making. It is not based on nuclear reactions that fuse atoms and molecules into something new. It is a more simple chemical reaction in which iron and oxygen are combined to produce a very useful material for all sorts of things.

Adding carbon to iron made Steel and changed the modern world in much the same way as adding tin to copper made Bronze and changed the ancient world. However, it was not all that easy, required some perquisites and so it took us some time. But now steel making is big business and major industry.

Metal Ages
Archaeologists divide human history by identifying the key metal used. The modern Three Age System was originally created by C.J. Thomsen (1788-1865) working as an antiquarian in the Danish National Museum in Copenhagen. Using principles of Aristotelian classification he arranged the collections by material into classes. The three-age system is so useful that it survives also in modern Archaeology although in significantly modified form.

Here is the schema with rough dates currently in use (early history in Eastern Mediterranean, some other regions may have lagged behind.)

Stone Ages 2 mya - 5000 BC.
First human tools were made of stones. Very soon people began to use silica (flint) because of the razor sharp edges it gives. Silicon is a kind of metallic mineral.

Chalcolithic (Copper/Stone) 5000 - 3500 BC
The use of copper in addition to stone tools identifies the Chalcolithic period.

Bronze Ages 3500 - 1200 BC
When copper was improved by adding a bit tin to the mixture a much harder metal was created called Bronze. This marks the beginning of the high River valley cultures.

Iron Age 1200 BC - 1600 AD
Most of the history familiar to us from school and books is from the period when Iron was the main material for tools. Since Iron Age is so long it is not practical and world history. Therefore archaeologists and historians use period names like Persian, Roman, Ottoman Turkish.

Steel Age 1600 AD - present

According to the schema based on metals we are living now in Steel Age. Since a dear child has many names, people commonly use terms like Plastic Age or Atomic Age. But the main metal for tools is definitely steel as future archaeologist of our settlements will also note.

Modern steel making
Making steel is not easy for humans and it took quite a time and some pretty smart people before it became reality. Introduction of steel making in Europe marks the beginning of the New Era and the rise of Western civilization, science and technology and first British Victorian rule of the world, then other Rulers of Steel passing in power even the Roman Rulers of Iron.

Since the 17th century the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace. Originally using charcoal, modern methods use coke, which has proven to be a great deal cheaper.

Processes starting from bar iron was used to make Blister steel and Crucible steel. In these processes pig iron was "fined" in a finery forge to produce bar iron (wrought iron), which was then used in steel-making.

The modern era in steelmaking began with the introduction of Henry Bessemer's Bessemer process in 1858. His raw material was pig iron. This enabled steel to be produced in large quantities cheaply, thus mild steel is now used for most purposes for which wrought iron was formerly used.

The Gilchrist-Thomas process (or basic Bessemer process) was an improvement to the Bessemer process, lining the converter with a basic material to remove phosphorus. Another improvement in steelmaking was the Siemens-Martin process, which complemented the Bessemer process.

These were rendered obsolete by the Linz-Donawitz process of basic oxygen steelmaking (BOS), developed in the 1950s, and other oxygen steelmaking processes. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limits impurities.

Now, electric arc furnaces (EAF) are a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electricity (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity


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