[MW:2680] RE: 2659] 304 & 304 L

Hamed,

 

304 is the general designation of a group of alloys all having nominally 18% Cr and 8% Ni and no other metallic elements added.  304 can have any carbon content up to a maximum of 0.8% C.

 

304 has several variations depending on carbon content and nitrogen addition.

The low carbon variations are preferred for water wetted service. Stress corrosion cracking, knife line attack, etc are controlled by preventing precipitation of Cr carbides (removing carbide from solid solution in the within the grains).  Precipation of Cr carbides is achieved by limiting the amount of carbon available to form them.  Room temperature strength is generally decreased.  The low carbon varieties have poor elevated temperature (creep strength) and are prohibite for use at elevated temperatures by ASME Code.  Nitrogen may be added to enhance strength of the low carbon variations at room temperature and at cryogenic temperatures.

• 304L  - nominally 18%Cr - 8% Ni, carbon < 0.03%
• 304LN - nominally 18%Cr - 8% Ni, carbon <0.03% and 0.010% < N < 0.16%

The high carbon variaion has elevated carbon content is intended for high temperature service (creep service).  Examples would be superheater tubes in fossil fueled boiler.

• 304H - nominally 18% Cr - 8% Ni, 0.04% < carbon < 0.10%

There is also an 304N variation that has the same general chemistry as 304, including carbon < 0.8%, but with the addition of 0.010% < Nitrogen < 0.016%   

 

Note that it is now common practice for most 304 to be produced with low carbon content and to be dual certified, i.e. 304/304L.  If you are going to use 304 at elevated temperatures you need to evaluate the chemistry carefully or specify 304H.

 

Hope this helps.

 

John 

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Hamed
Sent: Sunday, July 12, 2009 7:50 AM
To: materials-welding@googlegroups.com
Subject: [MW:2659] 304 & 304 L

Dear all

I want to know the difference between SS 304 & 304 L?

 

RGARDS

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