The following two web pages should have the information on surface roughness for which you are looking:

http://www.cs.rochester.edu/u/roche/rec.wood.misc/grit.sizes.html

http://www.sunnen.com/industrial/catalog/175.pdf

A No. 2B finish is a standard, as-rolled (not polished)finish for stainless steel.  The definition is a bright, cold-rolled finish resulting in the same manner as No. 2D finish, except that the annealed and descaled sheet receives a final light roll pass through polished rolls.  This is the general-purpose cold-rolled finish that can be used as is, or as a preliminary step to polishing.

I recommend that you perform a web search using www.google.com when you are trying to find information on an unknown subject.

A 2B finish on stainless will range from about 5 microinches Ra on lighter gauges, say 0.024 inch to 15 microinches on 0.187 inch. A 180 grit finish is equivalent to a number 4 finish which has a Ra of 5 to 15 typically. There is no standard.
 For more info see http://www.stainlesscenter.com FAQ's.