The history of stainless steel begins with its discovery (as probably expected) roughly 100 years ago. Up until 1911 there were a great many people from various countries (USA, Britain, Germany, France, Sweden, and Poland) claiming to have “invented” stainless steel but none of the were able to meet the minimum requirement of 10.5% chromium for their chromium-iron alloys. One big breakthrough that was very helpful in stainless steels discovery was by the French scientist Brustleina, who was able to figure out that the carbon content must remain below .15% in order to create an allow that contains a high content of chromium. This discovery delayed the development of stainless steel for 20 years as scientists were not able to create a low carbon chromium-Iron alloy.
In 1895 Hans Goldschmidt was able to create a process (the aluminothermic reduction process) that was able to produce carbon-free chromium which made the discovery of stainless steel possible.
The first version of what is considered today as stainless steel was developed by another French Scientist, Leon Guillet, whose first analysis of alloys that consisted of Iron, chromium, and nickel would be classified as 300 series grade stainless steel. Unfortunately, Guillet did not make any mention of the alloys ability to resist corrosion.
In 1911 the importance of having a minimum level of chromium in the alloy was discovered by a pair of German Scientists, Germans Monnartz and W. Borchers. The pair were able to figure out that there was a direct correlation between the alloys ability to resist corrosion and the level of chromium.
Harry Brearley, a British Researcher at Brown Firth Laboratories discovered and industrialized the first stainless steel alloy while attempting to create a corrosion-resistant alloy for gun barrels. However, the discovery was not publicly announced until 1915 when The New York Times published an article about the discovery. At this point stainless steel was still not yet stainless steel. The alloy discovered by Brearley was named and branded “Staybrite” by Firth Vickers. 1915 was also the year that Brearley first applied for a US patent where he discovered that US Scientist, Elwood Haynes had already applied for the same patent in 1912.
Elwood Haynes was not granted the patent until 1919. Brearley and Haynes ended up becoming partners and were able to found The American Stainless Steel Corporation in Pittsburg, PA.
There were many different brand names given to stainless steel and the actual name did not come about until 1921 when it was labeled an “unstainable steel” by a trade journal which then changed to stainless steel.
There were several other scientists and metallurgists across the globe that would make claims of discovering stainless steel alloys first but without the efforts and works of all of them, the stainless steel that we know and depend on so much would have taken much longer to be discovered, if ever at all. To give a much simpler answer to the question “who invented stainless steel?” the answer is typically Harry Brearley.