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Stainless Steel Stainless steel is a metal commonly used in consumer electronic devices. In the GPX AM/FM Stereo Receiver, model number A2935, stainless steel screws are used to hold the device together. There are many different types of stainless steel at different qualities and prices. Each type is used for different purposes. Using stainless steel for screws in electronics is a commonly used process that allows products to last longer and sustain more wear and tear. The following image shows a stainless steel screw in the back of the radio. Since GPX Inc. has not supplied our group with any information about the GPX radio, the material that the screws in the radio were made out of was unable to be specifically determined. Based on research, I was able to induce that the screws in the radio were most likely made of stainless steel. Other consumer products such as certain portable electronics and the metal casing of the iPod use stainless steel. The Casio EX-S100 digital camera also contains stainless steel screws (“User Rating for EX-S100...”). Physical Properties of Stainless Steel Stainless steel is used for making screws because of its unique properties. It is a shiny silver-colored metal. Wikipedia defines stainless steel “as a ferrous alloy with a minimum of 10.5% chromium content” (“Stainless steel”). A ferrous alloy means that it is a metallic compound containing iron and other elements. The high oxidation resistance of stainless steel is possible because of the chromium content. A layer of chromium(III) oxide forms when the stainless steel is exposed to oxygen. This layer protects the metal underneath from the elements but is thin enough that it is invisible to the naked eye; therefore, the metal will stay lustrous. When stainless steel is scratched, the layer of chromium oxide quickly reforms to protect the metal (“Stainless steel”). The following statistics from the  Australian Stainless Steel Development Association demonstrate the wide range of properties of differing grades of stainless steel.
(“Properties of stainless steel”) Grades of Stainless Steel There are many different types and grades of stainless steel. Austenitic stainless steels “contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point to the alloy” (“Stainless steel”). Cryogenic means the effects of very low temperatures. Austenitic means that the stainless steel has formed a crystalline structure that is non-magnetic and not as brittle at low temperatures. A common stainless steel seen in some screws is 18/8 stainless. It is composed of 18% chromium and 8% nickel. Some stainless steels are known as “superaustenitic” and demonstrate immunity from chloride pitting, crevice corrosion, and stress corrosion cracking. Pitting is caused by corrosion of stainless steel when oxygen is not present. According to Wikipedia, crevices and chloride can deprive stainless steel of the oxygen needed to form its protective layer. Austenitic stainless steels can undergo heat treatment to become very hard and usable for razor blades and cutlery. Ferritic stainless steels aren’t as durable as austenitic grades and cannot be hardened by heat treatment. They often contain molybdenum, titanium, or aluminum. Martensitic stainless steels are extremely strong, tough, easily machinable, and can be hardened by heat treatment. They are not as corrosion resistant as other types. Martensitic stainless steels contain high amounts of carbon (“Stainless steel”). Forming of Stainless Steel Objects Stainless steel is a very environmentally friendly material. It is 100% recyclable. “Over 50% of new stainless steel is made from re-melted scrap metal (“Stainless steel”). Milling is the main process for forming stainless steel into objects such as screws, nuts, and bolts. Milling machines are used for making complexly shaped metal objects. This is accomplished by removing unneeded material to from the final shape. Reasons for Using Stainless Steel in Screws Screws in GPX’s AM/FM Stereo Receiver were most likely made of stainless steel because of its resistance to corrosion. The metal is also relatively inexpensive. “Stainless steel fasteners cost only a small amount more related to a total project budget, but they can have significant effect on the life span of a structure” (Which grade of stainless steel...). Steel is very strong and inexpensive but reacts with air and water to form rust. According to Tim Carter, “If you never want to worry about rust and corrosion, you simply need to use stainless steel” (Stainless steel nails...). Because of the lack of documentation on the GPX radio, I am unable to cite the specific grade used in the screws. Stainless steel comes in 150 grades. The 200 series are austenitic iron-chromium-nickel-manganese alloys. The 300 series are austenitic iron-chromium-nickel alloys. The 400 series are ferritic and martensitic alloys. The grade of stainless steel in the screws is most likely to be in the 300 series. The 18/8 stainless steel mentioned above is grade 304 stainless steel. It will hold up to most elements except sea-water. This is a likely candidate for the screws in the GPX radio. Type 316 stainless contains 2-3% molybdenum and more nickel than type 304 and 305 stainless. It has greater survivability in a coastal or harsh environment (Which grade of stainless steel...). Carter claims that “316 stainless steel is the ultimate corrosion resistant alloy,” and that it will “resist attacks by just about anything you can throw at it” (Stainless steel nails...). Based on the properties and cost of stainless steel, I don’t believe GPX had any better choices for materials to use in their screws. Newer radios and products might not even contain screws on the outside of the device for visual appeal. For making screws, stainless steel still appears to be the best option. Stainless steel screws are milled into many shapes and sizes. They are used in many circumstances such as construction, consumer electronics, speakers, and computers. Stainless steel is the material of choice because of it is relatively inexpensive, hard, machinable, and very corrosion resistant. Screws made of this material are very common so it is not unexpected that GPX Inc. would use this type of screw in its consumer audio products. Sources Carter, T. Stainless steel nails, screws & fasteners. Retrieved October 25, 2005, from http://www.askthebuilder.com/B363_Stainless_Steel_Nails_Screws_Fasteners.shtml “Properties of stainless steel”. Australian stainless steel development association. Retrieved November 7, 2005, from http://www.assda.asn.au/asp/index.asp?pgid=17971 “Stainless steel”. Wikipedia, the free encyclopedia. Retrieved October 24, 2005, from http://en.wikipedia.org/wiki/Stainless_steel “User rating for EX-S100 digital camera (3.2MP, 2048x1536, 2.8x opt, 9.3MB built-in memory)”. PC world.com | Product finder. Retrieved November 2, 2005, from http://pcworld.pricegrabber.com/rating_getprodrev.php/product_id=5162117/id_type=M/ Which grade of stainless steel fasteners is best for my application. Retrieved October 25, 2005, from http://www.stainless-fasteners.com/which-stainless.htm |
