Ferritic grades: Ferritic stainless steels are magnetic non heat-treatable steels that contain
chromium but not nickel. They have good heat and corrosion resistance, in
particular sea water, and good resistance to stress-corrosion cracking. Their mechanical properties are not
as strong as the austenitic grades, however they have better decorative appeal.
Martensitic grades are magnetic and can be heat-treated by quenching or
tempering. They contain chromium but usually contain no nickel, except for 2 grades. Martensitic steels
are not as corrosive resistant as austenitic or ferritic grades, but their hardness
levels are among the highest of the all the stainless steels.
Austenitic stainless steels are non-magnetic non heat-treatable steels that are
usually annealed and cold worked. Some austenitic steels tend to become slightly
magnetic after cold working. Austenitic steels have excellent corrosion and heat
resistance with good mechanical properties over a wide range of temperatures.
There are two subclasses of austenitic stainless steels: chromium-nickel and
chromium-manganese-low nickel steels. Chromium-nickel steels are the most
general widely used steels and are also known as 18-8(Cr-Ni) steels. The chromium nickel ratio can be modified to improve formability; carbon content can be reduced to improve intergranular corrosion resistance. Molybdenum can be added to improve corrosion resistance; additionally the Cr-Ni content can be increased.