A potential new customer is having problems with their welding source in that many welds are cracking, and evidently there not willing to search out the reason why.
Material is 3/8" 1018 CRS rod with a small plate tacked on about 4" in from each end. The plate is a stamping say 1/8" x 1 x 1 1/2" 1010 CRS.
The plate is case hardened to 50 Rockwell & then Nickel plated before welding, many parts will develop a crack right threw the center of weld. I don't know what filler or process the other guy is using, yet it seems that no pre heat is involved and I assume he's using mild steel filler. I do know he is using the Tig process and adding a little filler wire.
What filler would work best? I would think that ones fighting the fact its case hardened.
I have now tried a 312 rod and seemed to work pretty good. I then tried a little pre heat and this seemed good also. I will next try a pre heat that where I am able to pick up parts and place in position on rod, then weld. I'm thinking around 150 degrees
Any thoughts here.
I think the problem is with the nickel plating. Centerline cracking is the result of either segregation induced cracking, bead shape cracking, or surface profile induced cracking. Segregation induced cracking occurs when low melting constituents such as phosphorous, zinc, copper and sulfur compounds in the admixture separate during the weld solidification process. Low melting components in the molten metal will be forced to the center of the joint during solidification, since they are the last to solidify and the weld tends to separate as the solidified metal contracts away from the center region containing the low melting point constituents.
I think the key might be the "adding a little filler" part. When only a little filler is added to what seems to be from your description a flare bevel goove weld, and with the contaminants picked up from the base metal treatments, you have a crack prone weld with a crack prone profile. If you add more filler, the profile of the weld will change from concave (which is crack prone), to flat or convex. Flare bevel groove welds have very little throat when the weld is concave. Add more filler, and make sure the weld is at least flat, if not convex. This will also have the effect of diluting the contaminants more. The worst contaminant could be (I'm not a plating expert, so you should confirm this) the high phosphorous or sulfer (don't remember which) that is present in the nickel plating.
Jer,
you're still looking at this problem since you first posted the question
on 04-Apr-06 14:48?
Here was my response then: By SWP On 04-Apr-06 17:14
I venture to guess the cracking is tied to the Nickel plating. I'm no expert on plating, but there is a process called High-phosphorus Electroless Nickel which contains 9 to 11% Phosphorus. Phosphorus is known to promote hot cracking.
Again a guess, but I don't think the case hardening is related to the weld centerline cracking. Generally, centerline cracking is hot cracking.
If the cracking occured in the basemetal HAZ, that might lead you to look at HAZ hardness and Hydrogen embrittlement. The base metal carbon is low, the very thin case is adding little carbon to the melt, it really shouldn't matter?
And here was my response when you posted in the Welding Web forum. Jerry,
was this question posted on another forum, I responded to this before? Do a web search on "nickel plating phosphorus" and you'll find that some nickel plating processes use up around 12% phosphorus. Phosphorus is an undesireable impurity in steels and is well known to cause "hot cracking" such as is generally indicated by a "center-line" crack.
I suppose you could calculate the carbon addition to the weld from the case hardened component, but I don't believe center-line cracking is generally associated with a hardened weld metal, I think it may tend to be more along the fusion line of the weld.
You know, some things are simply not weldable. Apparently, the last thing the customer thought about was the welding of this thing. You might do the customer a big favor by suggesting they properly design this thing with weldability in mind.
Thanks guys for all responses. Cracking is not always in center of weld, I have now seen more of these parts where cracking is in center and at base of welds. If I take this job on I would be doing it for a job shop who provides this to end customer. I asked about hardening & plating after welding, but seems they don't want to go there.
Ran some samples and here's what I found.
Tig filler Pre heat Hammer test
1) ER70S-2 NO Broke easily
2) Sil Bronze NO Broke but was better
3) 312 Stl. st. NO Broke but was better then both
4) 312 Stl. st 150 degrees Weld held, cracked base metal
5) ER70S-2 150 Same as above
Small pre heat seemed to give good weld and after hammering part back and forth actually started cracking the plated base metal
Try one with and without the plating with ER70S-6 but with the plate already surface hardened. The extra manganese in the ER70S-6 may help with the sulfur from the plating.
I think GROBERTS might be on to something.
The combo of the hardening and plating are more than likely part of the problem, but you may just not have enough filler. Are you getting complete joint penetration as well? Maybe you want to burn it in a lil' bit hotter with larger diameter filler, or just jam more in there on your dab. Definately aim for a convex weld, but just be sure you're not running to cold. Good luck!
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