Advanced Materials & Processes

FEB 2015

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

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portation industry. Automobiles used more trim and trucks were lined to carry milk, food, and acid. However, the most interesting use was on trains. Budd Man- ufacturing Co. designed the Zephyr, a passenger train made of stainless steel. It consisted of a locomotive, baggage car, and two passenger cars. From 1935 to the start of WWII, 47 stainless steel trains were manufactured using aircraft con- struction methods. The original Zephyr is now on display at the Museum of Sci- ence and Industry in Chicago. During the war, stainless steel was used extensively for aircraft exhaust systems and engine valves, ship galleys, and hardware wher- ever corrosion was a problem. alloy dEvElopMEnt Following WWII, several stainless steel producers developed alloys that respond well to precipitation harden- ing. Success was first achieved by The American Rolling Mill Co. (Armco). They kept the chromium content at 17%, but reduced the nickel to 4% and added 3.5% copper (17-4 PH) or 7% nickel with 1% aluminum (17-7 PH) and, a third alloy with 7% nickel, 2.5% molybdenum, and 1% aluminum. These alloys have design strengths of 200,000 to 220,000 psi after heat treatment. Another alloy system in development during this time was duplex stainless steels, which feature a microstructure of roughly 50% austenite and 50% ferrite to improve strength and corrosion resistance. aod procEss The major problem in ferritic and austenitic stainless steels production was the requirement for very low carbon con- tent to avoid precipitation of chromium carbides, which lower the chromium con- tent needed for corrosion resistance. This was a particular problem during welding, where a region in the heat-affected zone sits at the ideal temperature for carbide formation. Union Carbide Corp. (UCC) tried using an oxygen lance to reduce the carbon level, but was unsuccessful due to the uncontrolled temperature of the bath. They hired a recent MIT graduate named William A. Krivsky to work on improving the oxygen process. Krivsky tried adding the inert gas argon with the oxygen to control the bath temperature and carbon reaction. He successfully decreased the carbon to very low levels without exces- sive chromium loss. Following his labo- ratory success, UCC looked for a stainless producer to scale up the process to pro- duction levels. Only one company was in- terested—Joslyn Steel, a small producer in Fort Wayne, Ind. Over many years and many heats of steel, Joslyn was unable to produce a satisfactory result. They had tried intro- ducing oxygen and argon into the elec- tric arc furnace using lances coated with ceramics. Joslyn and UCC finally realized that the refining was going to need a separate vessel where argon was blown through the bottom, but oxygen was still introduced with a lance. The new vessel was similar to the old Bessemer converter and the technique became the success- ful argon oxygen decarburization (AOD) process. Union Carbide started offering licenses in 1970. As industry began to learn about the new process, more than 100 vessels were installed within a dozen years with 75% of world production even- tually using AOD. This was the greatest technological advance in the history of processing stainless steel. nEw and novEl applications A major use for stainless steel after WWII was for the exterior walls of high- rise buildings. The austenitic grade with 18% chromium and 8% nickel was select- ed for its corrosion resistance, formabili- ty, and added strength when cold rolled. The first design was the Socony-Mobil Building in New York. Within a few years, it was common practice to clad skyscrap- er buildings with stainless steel. It was also used for kitchen sinks in the late 1930s, later expanding to the exteriors of refrigerators, stoves, dish- washers, and other appliances. Although stainless has largely disappeared as auto trim and hubcaps, its current automotive use is for exhaust systems with catalytic converters and fuel injection systems. The chemical, pharmaceutical, and elec- trical power industries also use large amounts of stainless in piping, tanks, pumps, and other equipment. Stainless steel is the ideal metal alloy for designs requiring steel that does not rust. ~AM&P For more information: Charles R. Sim- coe can be reached at crsimcoe1@gmail. com. For more metallurgical history, visit tHE arGon oxyGEn dEcarbUrization (aod) procEss was tHE GrEatEst tEcHnoloGical advancE in tHE History of procEssinG stainlEss stEEl. Walt Disney Concert Hall, Los Angeles, designed by architect Frank Gehry. Public domain image. Socony-Mobil Building, the first high-rise to use a stainless steel exterior. Courtesy of SebasTorrente at en.wikipedia. Modern kitchen with stainless steel appliances. Public domain image. a d V a n c e d m a t e r i a l s & p r o c e s s e s | F e b r u a r y 2 0 1 5 3 3

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