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Welding 316L Stainless - Heat Input/Heat Affected Zone Rules

beh188 (Mechanical) (OP)
9 May 12 9:35
When welding 316L stainless, are there any code rules (ASME or AWS) that specify the heat input limits/control?  Is there a reason to be concerned about heat input for 316L stainless?

Also, is there any real heat affected zone for welded 316L stainless?  My understanding is that 316L is relatively insensitive to material property changes due to heat, and also is not sensitive to carbide precipitation.  I suppose that the grain size will get (larger?) in the heat affected zone, but I don't think this will have an effect on material properties assuming the material started as solution annealed.
brimstoner (Materials)
9 May 12 11:08
It depends.  

The practical problem is 'dual certified' stainless steels, which tend to have carbon contents that crowd the upper limit for L-grade.  In the region of 0.03~0.04% carbon there is a chance of sensitization, but it takes fairly extreme thermal conditions during welding to do this.  If you use normal welding processes and do not let the interpass temperature run away you should be quite safe.  

Dual certification is done purely for commercial reasons (less stock is required), but I take a dim view of it.  I know it won't happen but I believe that L-grades and straight grades should be made distinct by specifying a minimum carbon content for the straight grade.  The two types in general have quite different applications.  
 
stanweld (Materials)
9 May 12 11:37
The HAZ in 316L welds is still subject to sensitization. The normal precaution to mitigate sensitization is to llimt the interpass temperature to 350F.  

metengr (Materials)
9 May 12 18:52

Quote:

When welding 316L stainless, are there any code rules (ASME or AWS) that specify the heat input limits/control?

No, not for ASME. This is a process control detail.
beh188 (Mechanical) (OP)
9 May 12 21:17
Does the recommended interpass temperature of 350F come from AWS?  I have heard this temperature given other places, but wondered where it is defined.
brimstoner (Materials)
10 May 12 10:24

350° is just good practice. Not just for preventing sensitization, but for austenitic SS's very poor heat transfer properties.

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