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In metallurgy, stainless steel is defined as an iron-carbon alloy with a minimum of 10.5% chromium content.[1] The name originates from the fact that stainless steel does not stain, corrode or rust as easily as ordinary steel (it "stains less", but is not actually stain proof). This material is also called corrosion resistant steel when it is not detailed exactly to its alloy type and grade, particularly in the aviation industry. As such, there are now different and easily accessible grades and surface finishes of stainless steel, to suit the environment to which the material will be subjected in its lifetime. Common uses of stainless steel are everyday cutlery and watch straps.
Stainless steels have higher resistance to oxidation (rust) and corrosion in many natural and man made environments; however, it is important to select the correct type and grade of stainless steel for the particular application.
High oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.[2] The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, which means that the metal remains lustrous. It is, however, impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium.
Nickel also contributes to passivation, as do other less commonly used ingredients such as molybdenum and vanadium.
Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels. The molybdenum gives 316 better overall corrosion resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments. It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields. Grade 316 also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections.
Grade 316L, the low carbon version of 316 and is immune from sensitisation (grain boundary carbide precipitation).
The AISI 316L stainless steel has been widely used in artificial knee or hip joints, as well as internal fixation devices. It is well known that this material has a good corrosion resistance and acceptable biocompatibility properties ... ideal for watch bands and bracelets, etc.