I am tig welding 3/4" round solid bars together. It is actually a lifting link that is bent then the ends welded together. The proublem is when the weld gets pollished I am finding very small pin holes on alot of them. The part gets heat treated after welding so I am useing 4130 filler rod (3/32" Crown FH10). The ends of the bar are champhered at about a 30 deg. angle >< with about a 1/16" gap. At this point the champher can be changed if need be, because not to many are cut. I'm useing 100% argon set at 30 on the flow meter. After the root pass I am grinding the bottom side of it and am cleaning with a wire wheel in between the other passes. I am not useing preheat. I did try it at about 450 deg.F but saw no improvement. Any help with this would be greatly appreciated.
Thanks,
Hello unky adam, I believe there is a possibility that you are experiencing oxidation contamination due to having to use multiple passes to make this particular weld and you're experiencing improper shielding as this is being done. Short explanation: if I make a butt weld on a couple pieces of sheet without providing any backing protection, the backside of the joint will be subjected to temperatures that will promote oxidation and cause contamination that could compromise a weld on that side if it also requires additional welding.
A glovebox type of enclosure might provide the type of shielding of the joint that would prevent any of the sorts of contamination that you are experiencing when the part starts retaining a level of heat that puts it above a reactive temperature(the point where the temperature will promote rapid oxidation). The grinding of the backside of the root pass is certainly a good approach and using a wire wheel between passes is also a reasonable approach. I do feel that the wire wheel might not be getting rid of all of the oxidation that is needed to be removed. That is why although it seems extreme, in this case, it might be a good idea to opt for a glovebox type option. That's my $.02 for your consideration, I also look forward to suggestions from others to your question. Best regards, Allan
A glove box as Allan suggested would be a good method to try. However I would first take a long look at your preweld processes, especially cleaning of the base metal. A lot of folks think eh, it's just steel, a little mill scale can't hurt anything. I disagree, especially for chrome-moly steels. Also, you might want to review your max. interpass temperature. 4130 can be tricky if you get it too hot. If you're getting too much heat input, you might try going to a 1/8" filler and dropping a pass or two; i.e. fill it up faster. Either way, good luck and keep trying.
bozaktwo1
When I was cleaning before I would clean both sides and then weld both sides. I now see that I need to clean one side, weld, then clean the other side. I also went to the 1/8" filler and that gets rid of one pass on each side. They are looking much better but on some I'm still getting holes at the end of the last weld.
Another possible area that might be causing problems is the 4130 filler wire itself. I have it on good authority, Joe Scott of Devasco for those of you that know the gent, that in 4130 filler, unless you go to an aviation supplier, you generally get junk. Generally if you have bad wire, as an old TIG hand myself, you'll see something amiss in the puddle, but maybe not. You might try using ER110S-1 to see what happens on a sample. I would definitely use preheat on the thickness you mention, and for a lifting device, at least do a bake out afterwards.
Can the ER110S-1 be heat treated? Because this ring gets heat treated after welding. Thats why I went with the 4130 filler. We are also stress releaving at 1050 deg.F and holding for 1 hr. before they are sent to heat treat. I'll have to look into Devasco and see if they may have a better rod.
You could stress relieve ER110S-1 with 4130, but I'm not sure at all of renormalizing, quenching, and retempering. I'm not sure of the advantage of stress relieving prior to renormalizing. Most welded lifting devices are simply stress relieved. Be that as it may, by all means give Devasco a shout, they have a lot of knowledgeable people that I have found very helpful on several occasions. Just try to talk to the technical guys in real time instead of through the sales department. You'll get the same answers, but it will take less time.
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