Iron and steel continue to be vitally important to society. Steels are by far the most widely-used of metallic materials, worldwide the production continues to increase along with economic growth, with around 1000 million tonnes produced in 2004 (Source:IISI), one hundred and fifty kilograms of steel for each member of the worlds population. Obviously there are commercial pressures to maximise the profitability of production, there is also increasing environmental pressures on modern steel making.
The importance of steel is often overlooked or taken for granted, with even many steel producers even regarding it purely as a commodity. It’s true that large amounts of similar materials are produced by different manufacturers to commercial standards, for example automotive and construction markets. However the introduction of new materials for weight saving in automotive applications or the adoption of earth quake resistant steels after the Kobe earth quake in Japan show there is a requirement for innovation. Many steels are also produced in relatively low volumes to meet specific requirements, for example steel for nuclear reactors, tank armour, medical implants or jet engine components.
The importance of ferrous materials can arguably be traced back to before the iron age. Usage of iron increased rapidly during the industrial revolution when wrought iron was used extensively. The invention of the Bessemer process in 1855 greatly lowered the cost of production. Modern production of steel is based on a combination of the basic oxygen process in blast furnaces and recycling of scrap by melting in the electric arc furnace, production has increased steadily since 1950 (189 M tonnes to 1057 M tonnes in 2004). The energy consumption and CO$_2$ per tonne has decreased since 1975, in 2003 the average energy consumption (of companies reporting to IISI) was 19 GJ per tonne.
The complexities that have made ferrous alloys such versatile materials also have made them a fruitful area for research. The mechanical properties are controlled by a combination of alloying elements, mechanical and thermal processing, all of which affect the atomic arrangements in the steel. Significant effort is put into improving alloy design and manufacturing processes to achieve desirable properties in the most cost-effective way.
The use of the scientific methods of investigation into iron and steel really began with the optical microscopy studies of Sorby and Martens in the 19th Century. From 1860 to 1940 the major experimental techniques available and applied were optical microscopy, chemical and thermal analysis, dilatometry and X-ray crystallography. Important concepts introduced as a result of these investigations were allotropy, equilibrium, thermodynamics, solid-state transformation mechanisms and hardenability. The electron microscope and thin foil transmission techniques along with the concept of the imperfect crystal lattice has been important in ferrous metallurgy since the 1950s. Direct observation of atomic structure and defects on a surface was made possible with the atom probe microscope in 1955, and soon after with high resolution electron microscopes, and the scanning tunneling microscope. Experimental instruments continue to be developed and these improvements of instrumentation continually allow us to add to the range of knowledge.
The availability of modern computers has enabled theory to be consolidated into mathematical models which can be used to make predictions, or further aid our understanding, and also allowed the application of more flexible regression techniques to recognise patterns in experimental data.
Energy usage and CO2 in steel making
Increase in steel production
Properties of sheet steels and low-temperature bainite (After Sherif, 2004, PhD Thesis, Cambridge)
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