Marine grade stainless
Marine grade stainless alloys typically contain molybdenum to resist the corrosive effects of NaCl or salt in seawater. Concentrations of salt in seawater can vary, and splash zones can cause concentrations to increase dramatically from the spray and evaporation. SAE 316 stainless steel, is a molybdenum-alloyed steel and is the second most common austenite stainless steel (after grade 304). It is the preferred steel for use in marine environments because of its greater resistance to pitting corrosion than other grades of steel without molybdenum. The fact that it is negligibly responsive to magnetic fields means that it can be used in applications where a non-magnetic metal is required. A fully austenitic grade (super austenitic, low magnetism), even when cold worked, is Nitronic 50.  An example of a non-molybdenum grade performing well in seawater is Nitronic 60. "The pitting resistance of NITRONIC 60 in sea water is actually better than Type 316 due to the high levels of Si and N. The N also increases the yield strength..". 
While 316 is not completely rust-proof, the alloy is more corrosion-resistant than other common stainless steels. Surgical steel is made from subtypes of 316 stainless steel. In addition to molybdenum, 316 also contains a number of other elements in varying concentrations (see table below).
|SAE||% Cr||% Ni||% C||% Mn||% Si||% P||% S||% N||% Mo||Description and uses|
|316||16–18||10–14||0.08||2||0.75||0.045||0.03||0.10||2.0–3.0||General grade for food processing, chemical storage and transport, textile dying equipment, cladding of nuclear fuel, and oil refining equipment as well as some medical implants.|
|316L||16–18||10–14||0.03||2||0.75||0.045||0.03||0.10||2.0–3.0||Low-carbon grade for handling paper pulp as well as the production of rayon, rubber, textile bleaches, and high-temperature industrial equipment. This is the preferred grade for medical implants as it is resistant to sensitization (grain boundary carbide precipitation).|
|316F||16–18||10–14||0.08||2||1||0.2||0.10 min||-||1.75–2.5||Free-machining grade with reduced molybdenum and correspondingly increased phosphorus and sulfur for automatic machine screw parts as well as surgical implants and pharmaceutical processing equipment.|
|316N||16–18||10–14||0.08||2||0.75||0.045||0.03||0.10–0.16||2.0–3.0||High-nitrogen grade with increased resistance to pitting and to corrosion in crevices. Used for chemical handling accessories.|
Non-standard grades include 316H which has a "high" carbon content of greater than 0.04% giving it a high creep rupture strength at high temperatures, 316L(Hi)N which is an extra-high nitrogen grade (0.16-0.30%), 316Ti which is stabilized by titanium, 316Cb which is stabilized by niobium, 316L-SCQ which is a high-purity version of 316L, and 316LS which specially adapted for surgical implants.
Like other grades of stainless steel, marine grade stainless steel is a relatively poor conductor of both heat and of electricity when compared to metals and other conductive materials.
- Material Properties Data: Marine Grade Stainless Steel
- Metal Progress. American Society for Metals. July 1979.
- Eberhardt, Anthony J. Waterpower '89: Proceedings of the International Conference on Hydropower. Generators, Volume 3. American Society of Civil Engineers. p. 1428. ISBN 0872627233.
- Oberg, pp. 411-412.
- Joseph R. Davis (2000), Alloy Digest Sourcebook: Stainless Steels, ASM International, p. 8, ISBN 978-0-87170-649-2
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