Development of Stainless Steel
In the troubled years immediately before World War I, arms manufacturing increased significantly in the UK, but practical problems were encountered due to erosion (excessive wear) of the internal surfaces of gun barrels. Brearley began to research new steels which could better resist the erosion caused by high temperatures (rather than corrosion, as is often mentioned in this regard). He began to examine the addition of chromium to steel, which was known to raise the material’s melting point, as compared to the standard carbon steels.
The research concentrated on quantifying the effects of varying the levels of carbon (C, at concentrations around 0.2 weight %) and chromium (Cr, in the range of 6 to 15 weight %).
In order to undertake metallography to study the microstructure of the experimental alloys (the main factor responsible for a steel's mechanical properties) it was necessary to polish and etch the metallic samples produced. For a carbon steel, a dilute solution of nitric acid in alcohol is sufficient to produce the required etching, but Brearley found that the new chromium steels were very resistant to chemical attack.
It was probably Harry Brearley’s upbringing in Sheffield, a city famous for the manufacture of cutlery since the 16th century, which led him to appreciate the potential of these new steels for applications not only in high temperature service, as originally envisioned, but also in the mass production of food-related applications such as cutlery, saucepans and processing equipment etc. Up to that time carbon steel knives were prone to unhygienic rusting if they were not frequently polished and only expensive sterling silver or EPNS cutlery was generally available to avoid such problems. With this in mind Brearley extended his examinations to include tests with food acids such as vinegar and lemon juice, with very promising results.
Brearley initially called the new alloy "rustless steel"; the more euphonic "stainless steel" was suggested by Ernest Stuart of R.F. Mosley's, a local cutlery manufacturer, and eventually prevailed. It is reported that the first true stainless steel, a 0.24wt% C, 12.8wt% Cr ferrous alloy, was produced by Brearley in an electric furnace on August 13, 1913. He was subsequently awarded the Iron and Steel Institute's Bessemer Gold Medal in 1920.
Virtually all research projects into the further development of stainless steels were interrupted by the 1914-18 War, but efforts were renewed in the 1920s. Brearley had left the Brown Firth Laboratories in 1915, following disagreements regarding patent rights, but the research continued under the direction of his successor, Dr. W. H. Hatfield. It is Hatfield who is credited with the development, in 1924, of a stainless steel which even today is probably the widest-used alloy of this type, the so-called "18/8", which in addition to chromium, includes nickel (Ni) in its composition (18wt% Cr, 8wt% Ni).
After leaving Brown Firth, Brearley joined Brown Bayley's Steel Works, also in Sheffield; he became a director of the firm in 1925.
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