Loss of corrosion resistance in 316L SS

Date 05-09-2000 23:18

If the base metal is also 316L SS, there's nothing to worry about. The welded metal will have the same corrosion resistance as the base metal. But if the base metal is 316 SS (with no L), then you'll have corrosion problems due to dilution first (the 316L will pick up some of the carbon of the 316) and then to chromium carbide precipitation on the grain boundaries ( a problem known as "sensitization"). However, I'd guess that the base metal IS 316L (otherwise you wouldn't be using a 316L rod), so don't be concerned.
Giovanni S. Crisi
Sao Paulo - Brazil

By - Date 05-11-2000 16:34

Thanks so much for your kind, prompt reply.
BTW, we are not using any rod. The material is thin (.05") The weld would only involve the pieces of 316L SS being joined.
Do you know if there could be a problem of "crossing" at the overlap weld at the end of a circumferential seam weld?

Thanks again.....

Lynne

By fbrieden (***)

Date 01-24-2001 04:50

Please, I do not wish to insult any persons intelligence but, do the people involved here know what the L in 316-16L indicates?

By G.S.Crisi (****)

Date 02-02-2001 16:46

The suffix L indicates "Low carbon content". Most stainless steels pertaining to the 300 series (316 among them) have a carbon content of 0.08 percent when there's no L in the designation and 0.015 percent when the letter L shows up.
Giovanni S. Crisi
Sao Paulo - Brazil

By Jorge Giraldo (**)

Date 05-11-2000 00:12

Dear Lynne:
Both process, GTAW and resistance, imply fusion of the base metal for the join; then you will always obtain a heat affected zone (HAZ) around the weld metal and zones with temperatures range betwen 450C and 900C wich is the "sensitization range" for austenitic stainless steels. In this range the carbon reacts with the chromiun and forms "chromiun carbides" (Cr23C7 most of them) at grain boundaries; the trouble is the chromiun depleted zone around the carbides wich has a lesser corrosion resistance that the base metal. One way to avoid this situation is use a low carbon SS like yours (316L), because you have no enough carbon for the reaction with the chromiun. Then, like my friend Mr. Crissi said, you don't have to be concern with this weld, but I want to add something: if you have to do crossing welds, then you need to use filler metals with low carbon content (like the base metal) for avoid the presence of HAZ in weld metal (when you do a weld over other weld) with enough carbon for impair the corrosion resistance. If you need more help, please contact me.
Jorge Giraldo
Medellín, Colombia

By - Date 05-11-2000 16:31

Thanks so much for your kind reply. We wondered if the concern over crossing welds would apply to the overlap at the end of a circumferential seam weld.

Looking forward to your reply..... Thanks again.

Lynne

By MBSims

Date 01-27-2001 05:43

It sounds like you are looking at GTAW of 316L SS sheet with no filler metal (autogenous welds). In that case you could experience some hot cracking due to low ferrite levels. This could definitely cause you problems later on in a hot water heater, as it could lead to rupture of the weld and personal injury. You should consider making some test welds that duplicate what you plan to do in production and have them examined metallographically for ferrite and microfissures.

Marty Sims