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 | O C T O B E R 2 0 2 2 2 4 Some of the best practical metallurgists can be found in the kitchen. The kitchen is a fantastic array of metals, metal combinations, processed metals, and combinations such as the cladding of different metal layers. There is a maze of technologically competing metals such as aluminum, steel, stainless steel, cast iron, copper, brass, bronze, and cladding combinations. For example, in frying pans, a heat-conducting core of copper with outer protective stainless steel can be made by the cladding technique. Clad sandwiched metal combinations in pans are almost endless. Other metal combinations include the low heat-conductive stainless-steel handles on highly conductive aluminum or cast-iron bases. The sophistication of kitchen metallurgy has rivaled that of the aircraft and electronics industries in recent decades. Metallurgical terms like cryogenic hardening and HRC hardness are standard in the advertising for chef knives. Environmental and safety concerns require knowledge of lead, cadmium, aluminum, bismuth, and arsenic. A metallurgical background seems necessary to make purchasing decisions. This article focuses on the most prominent steel application in the kitchen—flatware. FLATWARE METALLURGY Consider kitchen steel metallurgy 101. Stainless steel is a metallurgically defined term, not a culinary term. When many people think of stainless steel, they think of sinks, appliances, and flatware. The highest quality stainless flatware is shiny, rust and stain-resistant, heavy, and non-magnetic. Had this stainless been available, Victorians would have gladly used it in place of silverware. The best flatware and kitchen sink stainless steel are in the 300 series. The 300 series formula of iron, chromium, and nickel was patented in 1924 by W.H. Hatfield of Sheffield, England, but many alloy combinations exist under the general Hatfield formula. Hatfield added chromium to an iron base for corrosion resistance and nickel to eliminate stains. The metallurgy of stainless flatware can be complex and nuanced in the application of chemistry. Metallurgy steels excel against corrosion, stain, and tarnish, making a beautiful flatware knife but a terrible cutting knife, steak, or chef knife. There are, however, ways to overcome this in an 18/10 or 18/8 flatware set. The combination of chromium and nickel defines the steel as 300 series. These high-quality 300 grades contain 18% chromium/10% nickel and 18% chromium/8% nickel. The 300 series also has low carbon to maintain softness and formability. Eighteen percent chromium is considered optimal for strong corrosion resistance. Eight percent nickel is the minimum for stain resistance. Metallurgically, 18/10 (type 305) and 18/8 (type 304) are 300 series stainless steel, but there is a difference. Type 305 steel (18/10) is the best to protect from corrosion, stain resistance, and luster needed for high-quality flatware, but is costly. Higher chromium content imparts better corrosion resistance but at a price. Chromium costs about $3/lb and is rising since Russia is a substantial supplier. Higher nickel improves the luster and stain resistance, but nickel adds a higher cost at $4/lb. Code 18/10 is optimal for stain resistance, luster, feel, and aesthetics. Selecting 18/8 over 18/10 is a mistake for the slight price difference. The lower nickel content of 18/8 will dramatically decrease flatware’s feel (heavy), luster, and stain resistance. The 18/10 (type 305) is considered the gold standard of flatware containing 18% chromium and 10% nickel. It has the weight and sheen approaching that of silver without the need for polishing. Type 305 is relatively soft, non-magnetic, and non-heat-treatable. It has a microscopic crystal structure PERSPECTIVE THE / (TYPE ) IS CONSIDERED THE GOLD STANDARD OF FLATWARE CONTAINING % CHROMIUM AND % NICKEL. defines the quality, performance, and price of flatware. Stainless steel for flatware is based on chromium and nickel content, but there are other minor alloying elements such as carbon that affect properties. Chromium is added for corrosion resistance and hardening. Nickel is added to aid in formability, reduce stains, and add luster to the finish. Flatware codes are based on % chromium content/% nickel content. There are four producer codes: 18/10, 18/8, 18/0, and 13/0. Note there are two levels of chromium content, 18 and 13%. The chromium and nickel code combinations represent a tradeoff of price and performance. The 13% chromium level is considered the minimum for corrosion resistance. Table 1 lists codes, types, and grades of several common tableware. The first two flatware codes (300 series) are 18/10 (type 305) and 18/8 (type 304). The 300 series stainless DINING METALLURGY 101 This introduction to the metallurgy of flatware describes the grades and qualities of metals used in typical cutlery and the reasons to choose one set over another. Quentin R. Skrabec, Jr. St. Eloi Consulting, Maumee, Ohio
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