Stainless steel reinforcement is sometimes used in marine structures.  Often when a long service life is desired, or where the environmental conditions are extreme.  Two different types of stainless steel reinforcement are available: Austenitic, or Duplex.  Duplex is a mixture of austenite and ferrite.  Duplex stainless steels are generally both stronger and cheaper owing to their lower Nickel content.

Within each type, there are a number of common grades: 

• Austenitic:  304 & 316.
• Duplex (austenitic-ferritic):  2101, 2304 & 2205.

The microstructure of stainless steel can be identified on site with use of a magnet.  If the stainless steel has a duplex microstructure, then a magnet will stick.  If it has an austenitic microstructure, then a magnet will not stick. 

In the photo attached, the diameter of the rebar is stamped on (i.e. 40mm diameter).  This helps with quality control, as it is easy for the builder & checker to identify that the correct size bars have been used.