Stainless steel grades
There are different Stainless steels grades with different corrosion resistance and mechanical properties:
Stainless Steel grades 200 Series.
This group of alloys is similar to the more common 300 Series alloys described below as they are non-magnetic and have an austenitic structure. The basic Stainless Steel Grades 200 alloy contains 17% chromium, 4% nickel and 7% manganese.
Although these alloys are somewhat more resistant to attack than the more common 300 series stainless steels, their overall performance is similar. Some proprietary grades related to the 200 series, have performance equal or superior to the best 300 series stainless steels.
These alloys are, however, not immune to attack and are very susceptible to concentration cell corrosion and pitting corrosion attack. When corrosion starts they usually corrode rapidly and nonuniformly.
In seawater immersion, the incubation time for
these alloys is in the range of 1 to 3 months with some of the Nitronic grades
having incubation times of up to 1 year.
Stainless Steel Grades 300 Series.
This group of alloys are non-magnetic and have an austenitic structure. The basic Stainless Steel Grades 300 alloy contains 18% chromium and 8% nickel.
These alloys are subject to crevice corrosion and
pitting corrosion. They have a range of incubation times in seawater ranging from
essentially zero in the case of the free machining grades, such as Type 303, to
6 months to 1 year for the best alloys, such as Type 316. They have been widely
used in facilities with mixed results. If used in an application where chloride
levels are low or where concentration cell corrosion has been prevented through
design, they are likely to perform well. When chloride levels are high and where
concentration cells can occur, the performance of these alloys is often poor.
They must always be selected with care for a specific application and the effect
of potential non-uniform attack on system performance must be addressed.
Stainless Steel Grades 400 Series.
This group of alloys are magnetic and have a
martensitic structure. The basic alloy contains 11% chromium and 1% manganese.
These Stainless Steel Grades alloys can be hardened by heat treatment but have
poor resistance to corrosion. They are subject to both uniform and non-uniform
attack in seawater. The incubation time for non-uniform attack in chloride
containing environments is very short, often only hours or a few days. Unless
protected, using these Stainless Stleel Grades in seawater or other environments
where they are susceptible to corrosion is not recommended.
Stainless Steel Grades 600 Series.
This series of stainless steels
grade is commonly referred to as “Precipitation Hardening” stainless steels.
These steels can be heat treated to high strength levels. They are subject to
crevice corrosion and pitting in chloride containing environments and are also
subject to stress corrosion cracking and hydrogen embrittlement.
The incubation time for crevice corrosion and pitting in seawater is relatively short, often only a few days. The incubation time for stress corrosion cracking can be very short, sometimes measured in hours.
The use of
these Stainless Steel Grade in chloride containing environments is not normally
recommended unless they are carefully selected, their heat treatment is
carefully specified and controlled, and the effect of pitting and crevice
corrosion is properly addressed.
source: MATERIAL DETERIORATION PREVENTION AND CONTROL GUIDE OF ARMY MATERIAL, PARTONE, METALS (MlL HDBK-73S (MR)
More info on Stainless Steel Grades:
Stainless Steel corrosion tables
Stainless Steel corrosion by waters
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