IRON THE ROOT METAL: Steel and stainless steel are both alloys of iron. The earliest recorded production of iron dates back to Anatolia (Turkey) in 2000 BCE. The Iron Age was well established by 1000 BCE.
Iron is a very soft metal. It can be moulded easily, but is not of much use. The carbon content of Iron ranges from 0.07% to 0.8%. A carbon content of less than 0.3% makes the iron very soft but if the carbon content is above 0.3%, iron becomes very hard and brittle. By 900 BCE the Egyptians developed the technique of tempering iron to make it more malleable, but at the same time retaining the hardness. Tempered iron was used to make swords and knives.
HISTORY OF STEEL: The Chinese were the first to produce heat treated steel. During the Han Dynasty (206BCE to 25CE) the Chinese started producing high carbon steel. In the course of the ensuing centuries, man learned to make steel from iron by adding carbon.
Many attempts were made to reduce the corrosive properties of steel and the anti-corrosive properties of chromium were noted as early as the 16th century. However the first commercially viable of a non-corrosive steel was developed as late as 1914 by Harry Brearley of Sheffield. This steel was christened stainless steel. It was an alloy of iron containing 0.4% carbon and 13% chromium. Brearley used it to produce cutlery.
PRODUCTION PROCESS: Steel is an alloy of iron and carbon. The carbon content does not exceed 2%. The process of quenching and tempering controls the properties of steel. The hardness and brittleness are reduced and the metal is strong and tough.
Stainless steel is produced by injecting argon and oxygen gas into liquid steel to reduce the carbon to the desired levels.
ADDITIONAL ELEMENTS: Other elements are added to steel in order to control its properties. These include nickel and manganese.
Additional anti-corrosive elements like nickel are added to stainless steel.
COST OF PRODUCTION: Both steel and stainless steel have comparably low production costs. The raw materials are abundantly available and the forming and processing is relatively simple and cost efficient.
CONCLUSION: Stainless steel is essentially a form of steel. Steel is the most widely used material in the world. A vast assortment of artefacts ranging from the lowly sewing needle to the lofty sky scrapers are all produced using steel. The tools and machinery used to produce almost everything – from seeds to space stations- are made from steel. The transportation the raw materials and finished products of anything and everything, is dependent on steel.
Despite the marginal differences between, steel and stainless steel dominate all aspects of our lives.
PROPERTIES: Steel has an impressive weight bearing capacity, making it the ideal metal for the construction industry as well as the railways, bridges, machinery, heavy vehicles and many other heavy industries. It is strong but malleable.
Stainless steel is easy to fabricate, has aesthetic appeal and hygienic properties. Its low carbon content makes it heat resistant. It is used for making surgical instruments, cutlery, home appliances, storage tanks etc.
CORROSION: The iron in steel combines with the oxygen in the air to form iron oxide, commonly known as rust. Rust is highly corrosive.
The chromium in stainless steel reacts with the oxygen in the air to form a chromium rich oxide film that coats the steel making it resistant to rust, stains and corrosion.