History
As with many of discoveries, it was the accumulated efforts of several individuals that actually began as far back as 1821 that lead to the discovery of stainless steel. In 1913 in Sheffield, England Harry Brearley was experimenting with steels for gun barrels and cutlery when he noticed that some sample material did not rust which he correctly attributed to the chromium content. He is generally accredited as the initiator of the industrial era of stainless steel with his patent in 1919.
The first product was table cutlery and it is still used today. The alloys which comprise the group of today’s stainless steels had their beginnings in Sheffield.
In 1913, whilst working at Firth Brown's research laboratory, Henry Brearley made the discovery that adding chromium to molten iron produced a metal that did not rust.
Chemistry
Stainless steels are iron-based alloys which ASTM A941 (2010b) defines as containing a minimum chromium content of 10.5 percent, and a maximum carbon content of less than 1.20 percent. The reinforcing bars commonly used today have a carbon content of less than 0.15 percent.
It is only with this stated minimum amount of chromium (10.5%) that a stable, transparent, passive and adherent surface film spontaneously forms to protect the surface of the metal from corrosive attack.
The different groups of stainless steels are categorized on the basis of the nature of their metallurgical structure. The exact chemical composition of the steel forms a specific and unique microstructure which is made up of the stable phases of austenitic or ferrite, or a duplex mix of these two.
