Update 7/23/2018:I added a small piece of new information on the development of 440C steel to the article.
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The writing of this article was made much easier due to the existence ofThe History of Stainless Steelby Harold Cobb . If you want more information on the history of stainless and the people who developed it, check out the book.
Nailing down one specific inventor of stainless steel is somewhat difficult; several people could be claimed as the “first” to analyze steels that could be called stainless. Part of the reason for the complexity is the fact that a critical mass of information, techniques, and available materials needed to exist for the inventor to connect everything together. A few of the important breakthroughs are as follows :
- Discovery of chromium in 1797 by Louis Nicholas Vauquelin
- Development of ferrochromium by Pierre Berthier in 1821. Ferrochromium can be added to molten iron to produce stainless steel. Ferrochromium at this time had a very high carbon content which made the production of stainless steel very difficult.
- A provisional British patent was obtained for an “acid- and weather-resistant” steel alloy with ~31% chromium in 1872, but the final patent was never filed.
- Hans Goldschmidt developed a method for producing low-carbon ferrochromium in 1895.
- A. Carnot and E. Goutal reported that high carbon contents reduce corrosion resistance of chromium-added steel in 1898.
- The development of chromium-alloyed tool steels and the use of higher hardening temperatures than was typically used in low alloy steels. These key discoveries were presented in 1900 and 1906 and led to rapid development of tool steels, which probably helped indirectly to spur the development of stainless steel as well. See The History of the First Tool Steel for more information.
- Leon Guillet is sometimes credited with the development of stainless steels. He published papers starting in 1904 where he analyzed the mechanical properties for high chromium steels. He looked at compositions that are similar to modern steels such as 410, 420, and 440C. However, his goal was to study the heat treatments, microstructures, and mechanical properties of high chromium steels. He did not discover until later the stain resistance of the studied steels, and is not known to have studied corrosion resistance. Also, while he is credited with 410, 420, and 440C, he was not necessarily attempting to develop specific steels but looked at a range of carbon and chromium contents, which happened to include combinations that look like those specific steel designations.
- In 1908 Philip Monnartz studied the effect of chromium and carbon on resistance to corrosion of steel in different environments including nitric acid, water and atmosphere. He published the results in 1911. He found that when the chromium content neared 12% that the resistance to corrosion greatly increased. He found that the corrosion resistance came from the “passivation” of the steel where an oxidizing condition induces corrosion resistance with high chromium steel. See How Much More Chromium Does D2 Need to be Stainless? for more information on passivation. He also found that low carbon steels did better in corrosion resistance because higher carbon led to carbides formed between chromium and carbon and thus reduces the free chromium in the steel. Molybdenum was also found to improve corrosion resistance by Monnartz.
Multiple Investigators in 1909-1912
There were multiple metallurgists look at high chromium steels for stain resistance at this time . Eduard Maurer and Benno Strauss developed chromium-nickel stainless steel between 1909 and 1912. Their steels became prototypes for modern steels 414 (12% Cr, 2% Ni) and 431 (16% Cr, 2% Ni), and also a steel very similar to the common austenitic stainless 18-8 which is used in conditions requiring very high corrosion resistance but is not used for knives. In 1911 Elwood Haynes was experimenting with the effect of chromium on corrosion resistance, hardness, and cutting quality. And Christian Dantsizen of the GE research laboratory was experimenting in 1911 with high-chromium steels.
Commercial Production of Stainless Steel
Harry Brearley, however, is credited with the start of industrial use of stainless steel , who was an employee of Firth Brown Research Laboratories. He discovered that steels with more than 10% chromium resisted etching and thought that such steels may be well suited for rifle barrels. In 1912, he produced an ingot with 12.8% Cr and 0.24% C and found it didn’t work well with gun barrels, but did in knives. Such a composition is very similar to modern 420 steel used today. This ingot is known as the first commercial cast of stainless steel. He reported the non-corrosive properties to several companies that might be interested, but received a negative response: “Nobody was impressed; perhaps the idea of producing on a commercial scale a steel which would not corrode sounded ridiculous.” The rusting of knives provides opportunities for people to buy more knives, after all.
This changed in 1914 when he convinced Ernest Stuart, manager of knife company R.F. Mosely’s, to try the steel. After a series of experiments they finally had success and forged and heated treated about 125 pounds of steel that was found to work well. Ernest Stuart is credited as the person who named the steel stainless, as he said that, “It stains less.” Prior to that Brearley had referred to it as “rustless” steel. Mosely ordered seven tons of stainless steel and other knife companies were also requesting orders of the steel. In 1915 the new steel was announced in the New York Times and also in advertisements:
Brearley went on to obtain patents in Britain, U.S., France, and Canada. His US patent was granted in 1916. He didn’t patent simply a stainless steel, however, but steel for cutlery. In fact, the patent is titled simply, “Cutlery.” Therefore, the first stainless steel was patented as a knife steel. There are wide ranges of composition given in the patent, but the typical composition is listed as 0.3% carbon, 13% chromium, and 0.3% manganese, the same as modern 420 steel used in knives. In the patent Brearley described his steel as “practically untarnishable when hardened” . After Thomas Firth & Sons learned of the patent they were concerned that there would be legal issues with their American subsidiary Firth-Sterling Steel Company in Pennsylvania. Firth’s directors agreed to purchase a half-share in the American patent, which ended the potential legal dispute. As part of the agreement, Brearley required that the Firth-Brearley Stainless Steel Syndicate would be formed “to foster the world-wide production of stainless steel cutlery.” During the first World War, Britain began using “Firth’s Aeroplane Steel” which was a stainless steel made for engine exhaust valves.
A patent was also granted to Elwood Haynes for stainless steel . Haynes was the inventor of Stellite, which continues to see some limited use in knives. Stellite is a cobalt-based alloy (not a steel) and is known for its very good corrosion resistance. Haynes had first filed his stainless steel patent slightly earlier than Brearley, but it was not granted until 1919. Haynes had to appeal arguing that his discovery was similar to Brearley’s but that they were made independently.The Firth-Brearley Stainless Steel Syndicate established a patent-holding company in the US to manage the licensing of the stainless steel patent, called the American Stainless Steel Company. Representatives of the company went to Haynes and offered him a position on the board and a 30% share in the new company. This avoided a court battle. This left the ownership of the American Stainless Steel Company as Firth-Brearly Stainless Steel Syndicate (40%), Elwood Haynes (30%), and the balance shared equally among Firth-Sterling Steel, Bethlehem Steel, Carpenter Steel, Crucible Steel, and Midvale Steel. Those steel companies, of course, were the first to license the patents to produce stainless steels. The combination of the two stainless steel patents made it very difficult for any company to produce stainless steel without paying the royalty, which was approximately 20%.
The Ludlum Steel company patented their own stainless steel in 1919 which used a significant silicon addition (3%) along with chromium (8%). The American Stainless Steel Company board attempted a settlement but the Ludlum Steel Company refused. The American Stainless Steel Company took them to court and in 1922 lost the case as the judge concluded that the silicon addition changed the steel significantly versus the original patents. They appealed the decision and won as the higher court concluded that the steel was stainless whether or not silicon was added.
The date that the American Stainless Steel Company ended is unknown, though in the early 1930’s they lost a suit with the Rustless Iron Company where their patent was not upheld, and Brearley’s patent also expired in the 1930’s.
Development of other Early Stainless Steels
Owen Parmiter, a metallurgist for Firth-Sterling Steel Company, wrote a paper on stainless steel in 1924, and updated it for 1935. He said in those papers that the original 420-type composition developed by Brearley continued to be the most popular version. However, in the updated 1935 paper he mentioned that a stainless steel with 0.7% carbon and 16.5% chromium had been developed . The higher carbon gives it higher hardness, with correspondingly higher chromium to maintain similar corrosion resistance to 420. That composition looks essentially like modern 440A steel, another common knife steel. I can’t find much information on when 440C was developed though it likely grew out of the existing 440A steel for applications requiring even higher hardness. I did find a patent for a bearing steel filed in 1940 with 0.9-1.1% carbon and 17-19% chromium; basically identical to 440C, though it’s not clear if the steel existed prior to the patent, as the patent focused on the production of bearings though the composition of the steel is a significant part of the patent . It was named 440C by at least 1944  and by 1949 it was called one of “the three most important grades of hardenable stainless steel in use today” .
Update 7/23/18:I found in the same 1935 book mentioned in the above paragraph  a reference to early 440C steel (though not called 440C, of course) by both Parmiter and more extensively by Morton and Rummler of Hoover Steel Ball Company and Machine Specialty Company. The high carbon 440C had begun to see use primarily as a bearing steel but other applications requiring high hardness, abrasion resistance, and corrosion resistance. Morton and Rummler stated: “While stainless steel as described in Section A of this chapter has been regarded as standard for cutlery and other implements to withstand attack of vegetable juices and animal extracts, the higher carbon, higher chromium steels now to be described have certain advantages. When properly heat treated they are equally resistant to tarnish or stain, and because of their greater strength and resistance to abrasion are better able to hold a sharp edge – wherein the early stainless steels were notably inferior to plain carbon cutlery steels.”
Update 8/17/20:I found that David Giles of Latrobe steel patented 440A steel in 1926-1927. Learn a bit more about him in this article. Giles, David J. “Steel alloy.” U.S. Patent 1,650,707, issued November 29, 1927.
Uddeholm in 1927 patented a stainless steel  with 0.7-1.1% carbon, 10-16% chromium, and 0.75-2.0% manganese, with a base composition of approximately 1% carbon and 13% chromium. This steel avoided the Brearley patent by having a minimum carbon content of 0.7%, which is right at the edge of the Brearley patent. Raising the carbon content with the same chromium content as 420 lowers the corrosion resistance but Uddeholm argued that the higher manganese content allowed the corrosion resistance to remain high. I am unable to find any research that indicates that manganese does indeed improve corrosion resistance, so I don’t think there is any validity to their claim . This Uddeholm steel was named AEB and later AEB-H. It has high potential hardness and good wear resistance and toughness but lower corrosion resistance than the 420 and 440-series steels. AEB was important in early stainless steel razors but was eventually replaced by AEB-L. Sandvik still makes a similar steel called 19C27.
Photo micrographs of 420, 440C, and 19C27 can be seen below. The carbide volume (white/grey particles) is much lower in 420 and the carbides are much smaller, which is because of its low carbon-chromium combination. Because of the low carbide volume and small carbides it has high toughness and ease in sharpening but lower wear resistance than 440 grades or AEB. 440C has a large volume of large carbides giving it high wear resistance but the lowest toughness of the three. AEB is an intermediate grade in terms of carbide volume, toughness, and wear resistance:
From reading the history it is apparent that the early development of stainless steel is greatly tied to knives. Stainless steel was so connected to knives in the minds of people that in 1926 it was reported that, “its almost exclusive use for cutlery purposes for a considerable period of time…has led to the belief, probably widely held, that stainless steel is simply a special type of cutlery steel” . Perhaps without the early adoption in knives it would have taken longer for the use of stainless steel to take off, or maybe even alternative materials would have been used for certain applications. It was this early development of stainless steel that led to the widespread use of 420 and 440A-class stainless steels in production knives and the common use of 440C in the custom knife market.
Cobb, H. M. “History of Stainless Steel.”Materials Park, OH, USA: ASM International,2010.
Brearley, Harry. “Cutlery.” U.S. Patent 1,197,256, issued September 5, 1916.
Haynes, Elwood. “Wrought-metal article.” U.S. Patent 1,299,404, issued April 1, 1919.
Thum, Ernest Edgar, ed.The book of stainless steels: corrosion resisting and heat resisting alloys. American Society for Metals, 1935.
Ulrich, Jelinek. “Method of making balls.” U.S. Patent 2,313,876, issued March 16, 1943.
Zapffe, Carl A., and M. Eleanor Haslem. “A Test for Hydrogen Embrittlement and its Application to 17 per cent Chromium, 1 per cent Carbon Stainless-Steel Wire.”Metals Technology13, no. 1 (1946): 1-28.
Zapffe, Carl Andrew.Stainless steels: an elementary text for consumers. American Society for metals, 1949.
Veges, Arved Eduard Gaston Theo. “Manufacturing edge tools and special composition of steel for same.” U.S. Patent 1,644,097, issued October 4, 1927.
Pardo, A., M. C. Merino, A. E. Coy, F. Viejo, R. Arrabal, and E. Matykina. “Pitting corrosion behaviour of austenitic stainless steels–combining effects of Mn and Mo additions.”Corrosion Science50, no. 6 (2008): 1796-1806.
Pardo, A., M. C. Merino, A. E. Coy, F. Viejo, R. Arrabal, and E. Matykina. “Effect of Mo and Mn additions on the corrosion behaviour of AISI 304 and 316 stainless steels in H2SO4.”Corrosion Science50, no. 3 (2008): 780-794.
Monypenny, John Henry Gill.Stainless iron and steel. Vol. 1. Chapman & Hall, 1926.