A brief history of stainless steels

Through the years there has been a lively discussion about who invented stainless steels and who made the first commercial heat. Today it is generally accepted that stainless steels were discovered in Europe somewhere in the early 20th century. There is still quite some discussion about where the first heat for a commercial application was produced though.

First developments

Harry Brearley, who was born in Sheffield, England, in 1871, probably invented stainless steel. His father was a steel melter and through private study and night school he became an expert in the analysis of steel and its production. In 1908 Brearley was given the opportunity to set up the Brown Firth Laboratories, which was financed by the two leading Sheffield steel companies of the day. In 1912 Brearley was asked to help solve 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.

Using first the crucible process, and then more successfully an electric furnace, a number of different melts of 6 to 15% chromium with varying carbon contents were made. The first true stainless steel was melted on the 13th August 1913. It contained 0.24% carbon and 12.8% chromium. At this time Brearley was still trying to find a more wear-resistant steel, and 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 re-agents he used 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. At the time, table cutlery was silver or nickel plated. Cutting knives were made of carbon steel, which had to thoroughly washed and dried after use, and even then rust stains would have to be rubbed off using carborundum stones. Brearley immediately saw how this new steel could revolutionise the cutlery industry but he had great difficulty convincing his more conservative employers. On his own initiative, he than had knives made at a local cutler's, R.F. Mosley. To begin with, Brearley referred to his invention as "rustless steel". It was Ernest Stuart, the cutlery manager of Mosley's who first referred to the new knives as "stainless" after, in experiments, he had failed to stain them with vinegar. "Corrosion resisting" steel would be really the better term, as ordinary stainless steels do suffer corrosion in the long term in hostile environments.

Other claims

Other claims have been made for the first invention of stainless steel, based upon published experimental papers that indicated the passive layer corrosion resistance of chromium steel or patented steels with a 9% chromium content intended for engineering purposes. One of these claims is based on an article in a 1913 Swedish hunting and fishing magazine about a steel that was used for, again, gun barrels. The steel seems to resemble a stainless steel so there are indications that the first commercial heat might have been produced in Sweden (see Stainless Steel World, April 2002, page 52-53).

German developments

Within a year of Brearley’s discovery, Krupp in Germany was experimenting by adding nickel to the melt. Brearley's steel could only be supplied in the hardened and tempered condition; the Krupp steel was more resistant to acids, was softer and more ductile and therefore easier to work. There is no doubt that but for Brearley's chance discovery, the metallurgists at Krupp would have soon made the discovery themselves. From these two inventions, just before the First World War, the "400" series of martensitic and "300" series of austenitic stainless steels were developed. The First World War largely put a halt to the further development of stainless steel, but in the early 1920s a whole variety of chromium and nickel combinations were tried including 20/6, 17/7 and 15/11. Brearley’s successor at the Brown Firth Laboratories was Dr W.H. Hatfield, who is credited with the invention in 1924 of 18/8 stainless steel (18% chromium, 8% nickel) which, with various additions. Today 18/8 is comanly known as 304 and still dominates the melting of stainless steel today. Dr Hatfield also invented 18/8 stainless with titanium added, now known as 321.a

Other grades

Most of the standard grades still in use today were invented in the period 1913 to 1935, in Britain, Germany, America and France. Once these standard grades became accepted, the emphasis changed to finding cheaper, mass-production methods, and popularising the use of stainless steel as a concept. This tended to stifle the development of new grades. However, after the Second World War, new grades with a better weight-to-strength ratio were required for jet aircraft, which led to the development of the precipitation hardening grades such as 17:4 PH. From the 1970s onwards the duplex stainless steels began to be developed. These have far greater corrosion resistance and strength than the grades developed in the 1920s and are really the future for the increasing use of stainless steel.