Precious Metals: Stainless Steel
Stainless Steel (Inox) Jewellery
Source: Man Made
The name "Stainless Steel" originates from the fact that this particular steel alloy is impervious to staining, inhibiting corrosion or rust that normally would occur with ordinary high-strength/low-alloy (HSLA) or carbon steel. The ferrous alloy, "stainless steel" or inox, has a minimum chromium content or 10.5 percent, forming what is known as a thin "passivation" layer of chromium (III) oxide, which protects against the corrosive effects of exposure to oxygen and salts. The passivation layer is too thin to be visible but is impervious to water and air, maintaining the luster of the metal under harsh conditions.
Harry Brearley of the Brown & Firth Research Laboratories in Sheffield, England is credited as the inventor of stainless steel in 1913. Similar industrial developments were taking place at the Krupp Iron Works in Germany, where Eduard Maurer was developing an austenitic alloy ("austenitic stainless steel") which was patented in 1912.
Molybdenum and vanadium can also be used as passivation agents in anti-corrosion alloys. When a higher level of hardness or tensile strength is required, carbon can be added.
Austenitic Stainless Steel
Austenitic stainless steel (aka 300 series) accounts for around 70 percent of worldwide stainless steel output. The typical composition of "austenitic" stainless steel is 18% chromium and 10% nickel, commonly known as 18/10 stainless, which is the alloy most often used in jewelry and flatware. Austenitic stainless steel contains a maximum of 0.15% Carbon, a minimum of 16% Chromium and sufficient Nickel and/or Manganese content to retain an austenitic structure at all temperatures ranges.
Stainless steel is a hard metal alloy which has a hardness of 5.5 to 6.0 on the Mohs scale, with a Vickers Hardness (HV or VHN) of between 200 and 240. the specific gravity of inox steel is 7.8.
Bibliography on Stainless Steel
1. American Iron and Steel Institute, Steel Glossary  . www.steel.org
2. Ask Dr. Steel, Why is Stainless Steel Stainless? . www.stainless-online.com
3. MacRAE's Blue Book (USA), Bar, Stainless Steel . www.macraesbluebook.com
4. Canadian Trade Index (CTI), Industrial Stainless Steel . www.ctidirectory.com
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