I tig weld and fabricate various medical equipment but mostly orthopedic surgical instruments mostly 17-4 stainless and occasionaly 316L,the set up i've inherited from a previous welder is Kemppi ac/dc 1200,watercooled torch,0.6,1.6mm thoriated tungstens,no gas lens,pure argon,one job in particular a simple pair of forceps with a pair of screw holding tips to be tigged on the ends,im using 20 amps,the arc is stable,gas flow is about 11cfh,im using 17-4 filler rods,this job is proving a nightmare because of the constant reworking of pinholes in the welded areas,its worth noting that in every 40 pairs of forceps i weld maybe half that will need reworking,im aware there could be a air being introduced into the weld area,or are there any contaminants associated with this particular s/s that im unaware of?some suggestions would be fully appreciated thanks.
17-4 Precipitation Hardenable steel should weld like butter... There are heat treat issues.. But the weld itself should not be giving porosity unless there is a process control issue out of whack.
No oxides, no plating, 11CFH may be a tad low unless you are using a very small diamater cup... But if a test weld with post flow produces a shiney surface finish you should be ok.... If your surface finish is grey and flakey you have a gas issue....
17-4 welds very easy with GTAW... It has a very very fluid shallow flat puddle.. you can see it quiver like quicksilver... The top of the puddle should show very little silica on the tip.. Not at all like inconels.
spido-
Don't know how well this will relate, but we struggled for a long time on another PH material, that being 13-8. I think most of our problems were related to cleanliness and gas quality. Now we clean every thing with alcohol, require welders to use NEW gloves and even wipe down the filler wire. The Argon we use is Mil rated which requires a few tests that UHP does not get. Our gas flow is 20-25 cfh, and always use gas lenses. We strictly abide by a low interpass temperature of 300 deg F, which for your Foreceps, I don't see as much of a problem. We run DCEN only. During PQR's I limited total heat input to 40kj/in and adjusted variables accordingly. I hope something here will be useful for you. Good luck.
By RonG 
Date 05-29-2008 01:30
Edited 05-30-2008 01:13
You use 17-4 filler? Why not ER630? We weld tons of 17-4 (GTAW) with out pin holes. A lot of it is 17-4PH cast material.
Your work is considerably smaller than ours, I suggest trying a gas lens, back purge or something to insure you have good gas coverage.
It could be, because the work is getting to hot for to long. The high Ni content will make a glass scale that will not remelt (at welding temps).
I would examine the gas supply system for leaks. Plug the torch off, initiate the solenoid to pressurize the entire line from the source to the torch, then leak check every single fitting, including the connection of the flow meter to the bottle, and the entire flow meter itself. It seems strange, but a leak will contaminate the shielding gas. Once you are sure the system is good, turn off the fan that keeps you cool while you weld, and get a gas lens. Let us know what you find is the solution.
