Alloy 17-4PH, TIG welding

[Kanuk]

On a test assembly for TIG welding alloy 17-4PH, fillet weld, single pass, I get fine cracking at weld toe. Anybody else experienced this?

 

[unclesyd]

Comeback with a little more information especially the condition that the 17-4 alloy is in.

Are you using a filler?

If so what type?

 

[Kanuk]

Most tests were done on solution annealed condition. Similar results were obtained with overaged at H1150.
The test assembly is made of a T joint, both members .125" thick, filler material is 17-4PH. Cracks are confirmed of intergranular type and shallow.

 

[metengr]

Sounds to me like you had contamination on the surface, prior to welding. How did you confirm the surface indications, visually or using liquid penetrant testing (PT)? Did you check for surface cracks anywhere else along the surface of the base metals being joined, away from the weld?

 

[Kanuk]

Indications are visual (10X). Actually, some of these indications do not respond well to fluorescent penetrant inspection. Surface contamination was our first hypothesis; surfaces were buffed and cleaned with alcohol. Microcracks parallell to main indication can be seen in close proximity (within .020" -.030").

 

[metengr]

Kanuk;
You need to have a metallurgical laboratory perform metallographic examination of the suspect locations to confirm the failure mechanism. The cracks need to be observed using an optical microscope to confirm their location (within grain boundaries or within grain interiors). Also, some work using the scanning electron microscope (SEM) may be required as part of the failure analysis. I would have a chemical analysis performed of the base metal, as well.

 

[Kanuk]

metengr, thank you for confirming this approach. Actually, most of these evaluations are underway or completed, and we have not confirmed yet a cracking mechanism. This is why I started this thread by asking if anybody else experienced cracking with this alloy; our experience does not fit with the available litterature indicating this alloy has no reported weldability issues.

 

[unclesyd]

I talked with the people that weld the majority of 17/4 in the fab shop and no one remembers any cracking problems. I wanted to make sure that I hadn't fell out out of the loop. When we were fabricating components form 17/4, + 17/4, + 4140, + 1030. The majority of the time the parts were weld in the H1125 condition, though welding on Condition A material didn't present any problems.
We normally used 308 electrodes or on some occasions we did use 630 electrodes. We welded to the 4140 with
Allstate 275 (312).

The cracking you describe sounds very similar to the shrinkage cracking experienced sometimes in the base metal when welding cast iron. My numbers for base metal and electrodes don't show this to be problem.

You state single pass welding, is this a full strength weld?

How is the heat input by the welder?

 

[Kanuk]

Sorry for the delay, I had to check few things.

Not sure what you mean by "full strength" weld. Final application may be a butt joint with full penetration in one pass (thickness ranging from .040" to .080", or a Fillet weld, also single pass.

Heat input: for the Fillet weld test, current is approximately 80 amps for a fillet size of .100" to .125". I estimate the welding speed to 3-4 ipm.

 

[9687]

17-4 material has copper in it that is heat sensitive. the throat of the weld needs to be convexed to prevent cracking on thin material. Butter the ends of joint with filler metal of 17-4PH start on tack or use run off tabs.Tell your welder to make the senter of the weld look like its bulging out whill they are welding.The welder needs to bring material melting temp up slow establish fusion then travel don't force it.That should solve your problems. Have a great day.

 

[Kanuk]

9687, thanks for the suggestions, we tried a convex weld profile and we still have the cracking at the toe.

 

[metengr]

Kanuk;
One last thought, what shielding gas are you using for GTAW welding 17-4 PH?

 

[9687]

Thought have you tried grinding the edges with scothbright brown prior to welding?

 

[9687]

There is also an old welders trick after grinding. use Zep contact cleaner spray on materal befor welding.

 

[GRoberts]

Making a weld convex usually helps for centerline cracking. I think that making it convex may only concentrate more stress at the toe of the weld, possibly exacerbating the problem.