We are getting material SS321 to machine flanges to be used in aerospace products. Within the past few months these turned parts, when welded don't act right. You can tell when you tack weld the flange that the material is "different." After welding the flange to a tube and wire brushing, the toe line at the flange side looks to be undercut. Under 10x, it is not undercut but a series of small pits in the base metal and it only appears on the flange side. None of these welds go through FPI without having to file the toe line of the weld to remove these pitted areas which is continuous all the way around. Checking the material certs, it has the right stuff, correct AMS number, everything! We x-rayed a couple of the welds to see if this condition showed up in the weld and they did not. The welds were clean. They are apparently only surface indications. Ever see anything like this? I am convinced something is wrong with the material. Is it the manufacturing process, heat treatment, excess impurities, I don't know. Appreciate any help you may have.
That is prety much the behavior of T 321. Due to the titanium and cosequent titanium stringers T 321 is not generally used in
aerospace applications. The prefered material is T 347 as it tends to have fewer stringers. Typically the only applications for
T 321 in aerospace were one time things like disposable tanks , not items requiring longevity .
What form is the flange, is it a casting, forginging, machined from plate etc.?
Have you performed any cross sections of the weld itself and viewed under magnification.
I have had silmilar results in 17-4 ss. It was a hub with forged flange on one side and a cast flange on the other side with a sheet metal cone between the two. I found all the problems on the toe of the weld on the casting side. We never did solve the problems and had to continue to bench the toe of the weld. All of the materials checked out fine. I would be interested to hear what others have to say as well.
JD
The raw material is in bar form. The flanges are machined from that. We can't really do any destructive testing because they are production parts. If a flange ever fails inspection after machining, I will use that one to perform cross sections.
I have not had to weld the material in question SS321. But I've had a similar problem welding C-276 Hastealloy with ENiCrMo-4 GMAW process. Looks like undercut but it's more of a pitting at the toe of the weld. My solution was to clean the material (Grind, Sand, or Solvent). In the end it was just surface contamination of the base metal. Hope this helps.
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