38 METALLURGYMetallurgy Lane, authored by ASM life member Charles R. Simcoe, is a yearlongLANE series dedicated to the early history of the U.S. metals and materials industries along with key milestones and developments. STAINLESS STEEL: THE STEEL THAT DOES NOT RUST — PART 1 ONE OF THE GREATEST ADVANCES IN MODERN METALLURGY WAS THE DISCOVERY OF A STEEL THAT DOES NOT RUST, WHICH OCCURRED AFTER RESEARCH INTO HIGH CHROMIUM STEELS BEGAN. rench researchers began adding all-austenitic microstructure was seen, it Albert Portevin and an Englishman, W. chromium or nickel to heat treated occurred at ambient temperature. Giesen. Portevin studied the straight Falloy steels during the 1880s and iron-chromium alloys with both low and 1890s, while German researchers began These three categories continue to high carbon. Giesen did most of his work ADVANCED MATERIALS & PROCESSES | JANUARY 2015 JANUARY | & PROCESSES MATERIALS ADVANCED combining chromium with nickel in the define the range of today’s stainless on the iron-chromium-nickel austenitic 1890s. These alloy additions were in steels. Guillet’s studies covered the steels, which had to be low carbon. Both the 2% to 5% range and required heat metallographic and mechanical published their results in the same edition treatment to achieve higher strength. properties that could be measured of the Iron and Steel Institute’s Carnegie during his era. However, he completely Scholarship Memoirs, Vol 1, 1909. Before 1895, there was no process for missed the fact that some of his alloys producing low-carbon chromium to be were resistant to corrosion in both acids added to iron. Further, controlling carbon and the normal atmosphere. They were DISCOVERY OF is the most important factor in making “stainless.” Because Guillet was the first STAINLESS STEEL chromium steels. At this point, German to publish on alloys that would later be The first researcher to discover the chemist Hans Goldschmidt invented classified as stainless steels, Carl Zapffe groundbreaking property of corrosion the thermite process, which combines in his classic Stainless Steels book (ASM resistance was Philip Monnartz of chromium ore with aluminum powder in a International, 1949) awarded him first Germany. He began his work in 1908 and heavy-walled container to generate enough place in the discovery of these alloys. published in the journal Metallurgie in heat to separate the chromium metal 1911. Quoting from Zapffe, “His research without carbon contamination. This paved Two other researchers who studied iron- disclosed the stainlessness of stainless the way to studying alloys with much higher chromium and iron-chromium-nickel steels—and provided as brilliant a chromium content and low carbon. alloys just a few years after Guillet include piece of work as stands in the literature the well-known French metallurgist on stainless steels.” First, Monnartz The first metals researcher to make use of this new low-carbon chromium was a Frenchman named Leon Guillet. He published his research during 1904- 1906 covering the full range of chromium additions that would later be alloys within the commercial range of stainless steel. Guillet’s work showed three basic alloy types: One was low carbon with high chromium that could not be hardened and therefore called ferritic. Another was higher carbon that could be hardened as any Hans Goldschmidt Leon Guillet was the first Philip Monnartz, the alloy steel and called martensitic. Finally, invented the thermite metallurgist to study inventor of stainless steel. he studied alloys with both chromium process. iron-chromium and iron- and nickel. With sufficient nickel, these chromium-nickel alloys. alloys were austenitic. The first time an 0115 AMP features.indd 38 1/9/2015 3:58:08 PM 39 ADVANCED MATERIALS & PROCESSES | JANUARY 2015 | JANUARY & PROCESSES MATERIALS ADVANCED determined that when the chromium this alloy a few years later for steam content exceeded 12%, the steel resisted “IT’S NOT SURPRISING turbine blades. attack by nitric acid and did not corrode in the normal atmosphere. Next, he found THAT IT TOOK SO Another American, Elwood Haynes, that the metal surface needed to be LONG TO DISCOVER worked on stainless steel with a higher prepared to form a protective film. This carbon content to produce a martensitic extremely thin film was the formation of STAINLESS STEEL. microstructure upon quenching from an oxide with a combination of iron and a high temperature. Haynes was an chromium when the chromium exceeded WHAT’S SURPRISING automobile manufacturer with an interest 12%. The tightly adherent film prevented IS THAT IT WASN’T in developing alloys for spark plugs. He further oxidation or corrosion. had already invented Stellite, a cobalt- DISCOVERED SOONER.” chromium-tungsten-carbon alloy used to He also found that low carbon content make hard and wear-resistant surfaces, is necessary to prevent formation of long to discover stainless steel. What’s such as valve seats. He applied for a chromium carbides and that carbon surprising is that it wasn’t discovered sooner.” patent in 1911 on a stainless steel alloy can be controlled by adding stronger that contained 13% chromium with 0.30% carbide formers, such as titanium, carbon, but it was held up for many years columbium, vanadium, molybdenum, STAINLESS STEEL due to interference with a British patent. or tungsten to form carbides of these APPLICATIONS ABOUND alloys rather than of chromium. Finally, The years from 1904 to 1911 were a major The British patent was held by Harry Monnartz learned that the addition of discovery period, while the following Brearley who had been searching for a 2% to 3% molybdenum greatly increased decade witnessed development of wear and corrosion-resistant alloy for gun the corrosion resistance of austenitic alloys for specific applications. The first barrels. This led him to a 13% chromium, stainless. His research provided the basic patent for a stainless steel alloy was 0.25% carbon hardenable stainless steel. He information for all future developments in German #246015, issued in 1910 to W. promoted his alloy—the forerunner of AISI practical alloys for the many applications Borchers and P. Monnartz, although the 420—for cutlery. It was a natural application that would develop for stainless steel. first application for stainless steel was for hardened knives and his employers for lead-in wires for electric lamp bulbs. were in Sheffield, UK, the capital of tool For his discovery, Monnartz must be The research was done by Christian and knife making. Brearley is credited with considered the one true inventor of stainless Dantsizen at the General Electric Research starting the first production of hardenable steel. While the other researchers, especially Laboratories in Schenectady, N.Y. Using stainless. The British military found that Guillet, were the pioneers of iron-chromium very low-carbon chromium made by the Brearley’s alloy was the answer for aircraft and iron-chromium-nickel steels, they Goldschmidt thermite process, he engine exhaust valves and requisitioned the completely missed the only property that developed an alloy containing 14% to available supply for the years 1914-1919. makes these alloys useful today. The mystery 15% chromium and 0.07% to 0.15% Thomas Firth and Sons made 50 tons for is this: How did they not notice that some carbon. His goal was resistance to knives before the war, a production lot of their alloys were so difficult to etch for oxidation at high temperature and considered to be the dawn of the stainless metallographic examination? As Zapffe the chromium provided that in a steel industry. quipped, “It’s not surprising that it took so ferritic microstructure. GE would use One of the most important patents issued for stainless steel went to Eduard Maurer and Benno Strauss working at the Friedrich Krupp Works in Essen, Germany. Their German patent #304159 issued in 1912 included, for the first time, austenitic stainless steel. One of their alloys contained 20% chromium and 7% nickel. With slight modification, this alloy became 18-8, the single most important stainless steel alloy ever produced. Elwood Haynes invented Harry Brearley launched Eduard Maurer patented martensitic stainless steel the production of the first austenitic For more information: Charles R. with 13% chromium and martensitic stainless for stainless steel in 1912. Simcoe can be reached at crsimcoe1@ 0.30% carbon. cutlery and tableware. gmail.com. For more metallurgical history, visit metals-history.blogspot.com. 0115 AMP features.indd 39 1/9/2015 3:58:08 PM.