Stainless Steel
 Ferritic stainless steels contain a minimum of 11% chromium. They are
relatively inexpensive as they contain no nickel. Ferritic stainless
steels are magnetic.
Austenitic stainless steels contain a minimum of 18%
chromium, along with a minimum of 8% nickel. They are non-magnetic,
which is a great advantage in many applications, especially marine
applications where unwarranted magnetic influence can affect compasses
and other direction finding equipment.
They also possess improved formability (e.g. deep
drawing or stretching) compared to ferritic stainless steels and are
tougher, maintaining their strength better at high temperatures.
Weldability is improved as is corrosion resistance, and, with the
addition of less that 2% molybdenum, corrosion resistance is
significantly improved.
Martensitic stainless steels contain a minimum of
11.5% chromium, generally with no nickel content but an addition of
0.15% - 0.4% carbon. These steels give very high strength in the
hardened condition. Tempering at 150°C to 170°C increases corrosion
resistance, and the abrasion and wear resistance of these alloys is well
known. Some variants containing high carbon content are not, however,
recommended for welding.
Duplex and Super Duplex stainless steels typically
contain approx. 22% chromium, 5% nickel and around 0.1% minimum of
nitrogen.
Effectively, they are of a mixed ferritic/austenitic
structure, and have high strength combined with good corrosion
resistance, good weldability, formability and resistance to crevice and
pitting corrosion in
chloride solutions.
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