welding 321 stainless

By SWP

Date 11-14-2005 15:36

Arc,
did a quick search for articles on 321 SS on AWS and came up with this abstract which mentions research suggesting some susceptibility to solidification cracking somehow related to the titanium in type 321, http://www.aws.org/conferences/abstracts/2003/15d.pdf. Further searching should yield more detail.

I am curious if the leak is typically located at the weld overlap, where the end of the weld continues over the top of the weld start.
I experienced hot cracking in Inconel 625 (related to the Niobium) that occured in heat affected zone (HAZ) or weld metal at the weld start. This cracking occured where the overlapping weld reheated this area and caused the low melting point grain boundary material to liquify and stresses associated with welding caused cracking.

You may be able to locate the leak by pressurizing the weldment and submerging in liquid. I have visually located very small leaks, first determined through helium leak detection, by this simple method using windex, but my parts were pressurized to 4000 psig and it took some time for very small bubbles form.

You might let us know what thickness, what is the form of the container, operating pressure, are you purging the inside, etc?
SWP

By arcvoice (*)

Date 11-14-2005 20:17

the leaks are at the edge or at thr haz area.. since I have been tracking this the seam of the welds seem to be fine..

By Lawrence (*****)

Date 11-14-2005 19:00

Do tell us more about your specific joint geometries, material thickness, manual or semi-automatic?

Groove welds? Fillets? outside corners?

If Semi-auto what is your travel speed, amperage, slopes and pulsation?

Are the leaks at start/stop points?

Are you reducing amperage to the point your metal has visibly frozen before the arc is extinguished at the end of your weld sequence?

321 stabilized with both Titanium and Niobium are routinely welded autogenously so we ought to be able deal with your leaks.

By SWP

Date 11-14-2005 19:31

Lawrence,
just a small point of clarification, from what I've read, 321 is Ti stabilized and 347 is Nb stabilized. Apparently, 347 is comonly used as a GMAW wire instead of 321 because Ti tends to be lost in the arc and is not fully transfered to the puddle.
SWP

By arcvoice (*)

Date 11-14-2005 19:55

from what I have read yes you are right.the ti is lost in the welding operation..

By arcvoice (*)

Date 11-14-2005 19:51

this is a butt joint where a end cap is fitted into a sleeve. the joint prep is on the top of the end cap. we weld these things at 15 amps with 90% 10 H2 gas under a inclosed atmosphere. the welds leak under a helium mass spec test. the cap thickness is .125 and the sleeve is .010. There is a joint prep groove machined into the cap . The leaks always seem to be located in that groove which is next to the welded area. I have not been able to find the leak. Very small but it is there.. I'm thinking the H2 and the Ti do not get along when welding.. If the parts at not perfectly clean I believe I am seeing a h2 leak..

By arcvoice (*)

Date 11-14-2005 19:53

this is a manual gtaw welding operation with no filler metal used.

By SWP

Date 11-15-2005 00:21

Interesting problem.
If you can do metallography, or send out and have it done, you may get lucky and be able to actually see a magnified cross section of the leak path, which may give a better clue as to the failure mechanism, such as weld metal solidification cracking, HAZ hot cracking. But it may be that problem is basically due to the material chemistry, and if you are stuck and cannot change material type or lot of material, you may simply be stuck with an elevated failure rate. This happened to me with Inconel 625 product.

You can of course tighten up everything about your material handling, cleaning, and weld process, and maybe even try changing the process somehow. Sometimes none of this helps.

A couple things to think about.
Hot cracking in some alloys does occur in the heat affected zone.
Leaks can occur from inclusion stringers within the base metal, having nothing to do with the weld. I've seen this in some alloy steels, but kind of doubt that a stainless steel would have stringers to this degree.

Let us know what you find.

By arcvoice (*)

Date 11-15-2005 12:39

I have a part sent out to be evaluated. that is 718 to 17-4 material same type of problem.. Around here 347 is common and does not seem to cause failures.. this product line came from another company which uses the 321. since the material is thin and small I believe that it is a hot cracking situation in the haz.. I have tightened the cleaning and looked over the welders to see that they are not over heating the parts. If the parts are to fail due to chemistry, is there any way to pretreat the material before welding to help myself out.