Corrosion handbook
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Another severe form of corrosion relevant for stainless steel is stress corrosion
cracking. Austenitic stainless steel can be prone to this form of corrosion under
specific highly aggressive environments such as in indoor swimming pools. In
such cases, highly corrosion-resistant grades of stainless steel must be used for
some applications, e.g. grades with a molybdenum content of more than 6 %.
You will find more information about selecting stainless steel grades in section 4.
Stainless steel grades
There are various grades of stainless steel with different levels of stability. The
most common grade is alloyed with around 18 % Cr and 10 % Ni (see Fig. 33).
Increasing or reducing the amount of specific elements in the steel changes its
corrosion properties, its mechanical properties or some processing properties
such as weldability. If the nickel content is significantly reduced the alloy phase
will no longer be purely austenitic, but will then combine austenitic and ferritic
phases (duplex stainless steel). Additionally to these grades, there are the
martensitc stainless steel grades.
Stainless steel designations
The illustration in Fig. 33 shows the three most common forms of stainless steel
grade designations:
7L
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1L
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1L
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Fig. 33: Classification tree for the most common austenitic and austenitic-ferritic
stainless steel grades. The Roman numbers indicate the corrosion resistance
class (see also 4.3)