Tuesday, October 11, 2005

Invention of Stainless Steel

Stainless steel, the name doesnt sound like a puzzle of alien world. Everyone must be familiar of this metallic alloy and its uses in our daily life. Main property which makes it so popular and useful is its excellent corrosion resistance, which is attibuted to the presence of metal Chromium in this alloy system. Infact, stainless steel is defined as ferrous alloy containing more than 10.5 % Chromium (by weight). Other main alloying elements are Molybdenum and Nickel. More information about this interesting iron alloy can be found here and here.

Just like other major inventions, stainless steel was also an accidental invention. This is accredited to Harry Brearly from Sheffield, UK in 1913. Interesting fact is that he left school at the age of 12 and then by private studies and night school he became an expert in steel analysis. In 1912 Brearley was asked to help in the problems being encountered by a small arms manufacturer, whereby the internal diameter of rifle barrels was eroding away too quickly because of the action of heating and discharge gases. Brearley was therefore looking for a steel with better resistance to erosion, not corrosion. As a line of investigation he decided to experiment with steels containing chromium, as these were known to have a higher melting point than ordinary steels.

He made a number of different melts of 6 to 15% chromium with varying carbon contents. The first true stainless steel was melted on the 13th August 1913. It contained 0.24% carbon and 12.8% chromium. In order to examine the grain structure of the steel he needed to etch (attack with acid) samples before examining them under the microscope. The etching reagents were based on nitric acid, and he found that this new steel strongly resisted chemical attack. He then exposed samples to vinegar and other food acids such as lemon juice and found the same result. Thus, a corrosion resistant variety of steel was born, which was later named as Stainless Steel.


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