History of Steel Making

Introduction
Steel is a form of Iron with most impurities removed. Iron is a chemical element. It is a strong, hard, heavy gray metal. It is found in meteorites. Iron is also found combined in many mineral compounds in the earth's crust. Iron rusts easily and can be magnetized and is strongly attracted to magnets. It is used to make many things such as gates and railings. When Iron is used to make steel, the product is an even harder and tougher metal compound. Steel is formed by treating molten (melted) iron with intense heat and mixing it (alloying) with carbon. Steel is used to make machines, cars, tools, knives, and many other things.

Iron smelting and iron works are as old as history is recorded. Archaeologists in Egypt discovered iron works dated from about 3000 BC, and iron ornaments were used even earlier; the comparatively advanced technique of hardening iron weapons by heat treatment was known to the Greeks about 1000 BC.

Wrought Iron
Earlier iron works and iron alloys made until 14th century are classified as wrought iron. They were made by heating a mass of iron ore and charcoal in a forge or furnace having a forced draft. Under this treatment the ore was reduced to the sponge of metallic iron filled with a slag composed of metallic impurities and charcoal ash. This sponge of iron was removed from the furnace while still incandescent and beaten with heavy sledges to drive out the slag and to weld and consolidate the iron.

The iron produced under these conditions usually contained about 3 percent of slag particles and 0.1 percent of other impurities. Occasionally this technique of iron making produced, by accident, a true steel rather than wrought iron. Ironworkers learned to make steel by heating wrought iron and charcoal in clay boxes for a period of several days. By this process the iron absorbed enough carbon to become true steel.

Pig Iron
After the 14th century the furnaces used in smelting were increased in size, and increased draft was used to force the combustion gases through the “charge,” the mixture of raw materials. In these larger furnaces, the iron ore in the upper part of the furnace was first reduced to metallic iron and then took on more carbon as a result of the gases forced through it by the blast. The product of these furnaces was pig iron, an alloy that melts at a lower temperature than steel or wrought iron. Pig iron (so called because it was usually cast in stubby, round ingots known as pigs) was then further refined to make steel.

Blast and Electric Furnaces
Modern steelmaking employs blast furnaces that are merely refinements of the furnaces used by the old ironworkers. The process of refining molten iron with blasts of air was accomplished by the British inventor Sir Henry Bessemer who developed the Bessemer furnace, or converter, in 1855. Since the 1960s, several plants, including QATAR STEEL, have been producing steel using electric furnaces.