Stainless Steel Grades

Here is the information you request.

What distinguishes Type 316 from Type 304 is the addition of molybdenum up to a maximum of 3%.
http://bosunsupplies.com/StainlessInfo2.cfm

The numbering system that uses 2xx, 3xx, 4xx, 5xx, etc is by the American Iron and Steel Institute (AISI)

[from machinery's handbook]:

Standard Steel Numbering System.

The most widely used systems for identifying
wrought carbon, low–alloy, and stainless steels are based on chemical composition, and
are those of the American Iron and Steel Institute (AISI) and the Society of Automotive
Engineers (SAE). These systems are almost identical, but they are carefully coordinated.
The standard steels so designated have been developed cooperatively by producers and
users and have been found through long experience to cover most of the wrought ferrous
metals used in automotive vehicles and related equipment. These designations, however,
are not specifications, and should not be used for purchasing unless accompanied by supplementary
information necessary to describe commercially the product desired. Engineering
societies, associations, and institutes whose members make, specify, or purchase
steel products publish standard specifications, many of which have become well known
and respected. The most comprehensive and widely used specifications are those published
by the American Society for Testing and Materials (ASTM). The U.S. government
and various companies also publish their own specification for steel products to serve their
own special procurement needs. The Unified Numbering System (UNS) for metals and
alloys is also used to designate steels (see pages 403 and 405).
The numerical designation system used by both AISI and SAE for wrought carbon, alloy,
and stainless steels is summarized in Table 3 . Table 2 lists the compositions of the standard
carbon steels; Table 4 lists the standard low–alloy steel compositions; and Table 5 includes
the typical compositions of the standard stainless steels.

AISI SAE Stainless Steels
2xx 302xx Chromium–Manganese–Nickel Steels
3xx 303xx Chromium–Nickel Steels
4xx 514xx Chromium Steels
5xx 515xx Chromium Steels
a xx in the last two digits of the carbon and low–alloy designations (but not the stainless steels) indicates
that the carbon content (in hundredths of a per cent) is to be inserted.

[end quote]

If you need the tables let me know.

cheers,
d.g.whiskey

> Total agreement with what competently reported by our colleague d.g.whiskey , except for this info: out of United States in technical & scientific environmet too, the Aisi/Sae codes are used as specifications for the designation of steels in commercial contracts, particularly referring to stainless steel. Not a nice but a "comfortable" practice . . . After this, it may happen that someone is "inventing" new designation as "SS 3xx" . . . , never heard & very similar to AISI & SAE. Be carefull they can be tricky. In these events it is important to ask detailed compositions and explications, a copy of the norms and designation tables to which the code is referring is always to be asked. As already written, unless you know very well & you trust your supplier, you cannot lie the quality of your production on fancy shortnames.

these are called Austenitic stainless steels. When Chromium (Cr)and Nickel (Ni) is added to steel it becomes stainless steel. depending on the percentage of these elements added it gets its grade. now 18% Cr and 8% Ni is called SS 304 grade. Added to this if 2 % molybdenum is added, it becomes SS 316. there is no SS 306 grade available. 20%-10% is called SS310. and the list goes on. you go to ASME Section 2 part A and you will see all these things.

As someone else said the 300 series is the austenitic series of Stainless Steel, which means they have austenitic structure. There is not a direct correlation between the number 304.. 316.. and the composition but you have to look into chart or table to find the exact composition.

hope this helps

S