[dmeray1@hotmail.com]

While cleaning and inspecting my Go Kart I think I found a crack next to the rear bearing hanger. I will clean the area to make sure it is a crack before trying to weld it up. I will weld in a gusset from the bearing hanger to the frame rail after I weld the crack. Any words of wisdom before I start would be appreciated.

[BugHunter]

If there was enough fatigue to crack that where it did, I would be inclined to cut that entire section out and replace the entire junction of the two parts. Ymmv.

[cj737]

From the picture, I can’t see a definitive crack but I do see a crappy weld. If there is a crack, I’d grind out the weld there and the adjacent horizontal and re-weld them properly. Stress cracks from poorly penetrated welds are surefire and additional gussets won’t prevent them.

[Poland308]

Stop drill the crack, cut it out or grind it out, pre heat, post heat, lots of Argon.

[Spartan]

Weld it hot. If you need to stop to let the part(s) cool down, let it cool naturally. Don't put even a fan on it, and certainly don't quench anything.

[sbaker56]

As spartan said if that cage really is 4130, definitely don't let it cool too fast, that's the bane of that kind of steel, you can end up with a hard brittle HAZ very easily if you're not careful. I would preheat the area, and also control the cooling if possible, I've heard of people using ceramic insulation, but as that may be hard to find and or apply, you might consider just passing a propane torch over the area periodically applying just enough heat to slow the rate of cooling.

[BillE.Dee]

can't tell IF you have a real crack in the weld, but I'd kinda think that the paint would be chipping if it was moving. Clean the paint out of the way and see if it is a crack and how far it runs. Stop drill it, both ends, slight cut and reweld it

[Jakedaawg]

What level of go-kart are we talking about that has a 4130 frame? Is this some kind of race deal? I put together one for a nephew and all the welds had to be x-rayed, granted this wasn't your typical go-kart. We ended up sending it to a buddy of mine who welds dragsters and had the ability to get it tested.

[dmeray1@hotmail.com]

I cleaned the area and it looks like a crack for sure. I'll stop drill it. Would a slight grind of the crack to create a slight V shape be of any use or just weld on top of the crack?

[TraditionalToolworks]

Looks like a bad weld to me, not a crack, but what do I know...

I recommend grinding out the weld so you can see exactly what is going on there.

[Poland308]

Yes grind out a v. It’s a stress crack on the toe of a weld in the haz. Not uncommon.

[Coldman]

And maybe put in a gusset as well.

[Spartan]

Yes grind out a v. It’s a stress crack on the toe of a weld in the haz. Not uncommon.

^^^This

I'd give that a solid preheat before welding again.

[dmeray1@hotmail.com]

Filler rod recommendations? I have ER80S02 and ER70S06.

[Poland308]

https://www.harrisproductsgroup.com/en/ ... -Moly.aspx

[Spartan]

I use 70s2 for 4130. Can't speak to the others. I had started a thread asking about that months ago and got some good responses. Do a quick search for that thread.

[Oscar]

https://www.harrisproductsgroup.com/en/ ... -Moly.aspx

Correct me if I'm wrong, but using 4130 filler would necessitate an intricate PWHT.

I use 70s2 for 4130. Can't speak to the others. I had started a thread asking about that months ago and got some good responses. Do a quick search for that thread.

Yup.

Demaray1,

According to Jerry Uttrachi, ER70S-2 is the best choice. ER80S-D2 yields higher tensile strengths but has a higher susceptibility for post-weld cracking if it cools too quickly because it has higher levels of molybdenum and manganese, both of which are elements that produced increased hardness (by way of increased martensite). It can be mitigated with pre-heat and post-heat to slow the cooling rate, but ER70S-2 would be very close without the added hassle.

[Poland308]

Any work on that frame no mater the filler should have a pre / post heat. Your best results in a situation like this is a filler that matches the base metal. You can get wax temp sticks from most weld suppliers, for the temp ranges you need. Frame work also has an interpass temp, with temp sticks it’s super easy to do a proper pre / post heat on a small repair like this , especially on thin tube.

[Oscar]

I agree pre/post-heat helps, but I respectfully disagree on using a filler that exactly matches 4130, meaning 4130 filler rod. From the research I've done, if using 4130 filler rod, the weld has to then raised to ~1,675°F, quenched in water or oil, then slowly brought up to a temperature above 400°F (depending how much ductility is to be restored). Otherwise there will likely be too much martensite left in the weld area.

Source: Advanced Automotive Welding, Jerry Uttrachi, Car Tech Inc, Jan 2012.

Other sources I've read also point to the same idea as that above.

[cj737]

I use ER80 more than ER70 for CroMo tubing. I do not agree that pre- and post-heat are necessitated by the material dimensions. CroMo that is thick (generally 1" or better) demands heat treatments. But the wall thickness of that tubing is likely <0.93 and heating it won't materially effect the outcome.

Yes, grind it out as best you can. A gusset too is a good idea. But mostly, proper welding (I am suspicious of the original weld) should be adequate. I've done ample motorcycle frames and not once had an issue with cracks with ER80. Swing arms too.

I do on occasion, simply because with frames I am anal, purge the tubing while welding. It's a modicum of insurance to insure the best weld possible.

[Poland308]

https://www.harrisproductsgroup.com/~/m ... MOSpec.pdf

Spec sheet from previously posted link. Interpass of 400. Preheat required but obviously that would be less than 400f.

[Spartan]

I agree pre/post-heat helps, but I respectfully disagree on using a filler that exactly matches 4130, meaning 4130 filler rod. From the research I've done, if using 4130 filler rod, the weld has to then raised to ~1,675°F, quenched in water or oil, then slowly brought up to a temperature above 400°F (depending how much ductility is to be restored). Otherwise there will likely be too much martensite left in the weld area.

Source: Advanced Automotive Welding, Jerry Uttrachi, Car Tech Inc, Jan 2012.

Other sources I've read also point to the same idea as that above.

My understanding of using 4130 filler, and I think this is what Oscars is getting at, is only use it if the part needs to be HARDENED after welding. Using 4130 filler in that application allows the weld to be properly hardened as well.

I imagine the OP will not be hardening their go-cart frame.

[LtBadd]

if you go to Jody's YT channel and do a search for 4130 several videos come up, there is 1 from a year ago that may address this "TIG Welding 4130 Chromoly Tubing" it may be good to watch as there has been much debate on this topic.

[BugHunter]

My understanding of using 4130 filler, and I think this is what Oscars is getting at, is only use it if the part needs to be HARDENED after welding. Using 4130 filler in that application allows the weld to be properly hardened as well.

I imagine the OP will not be hardening their go-cart frame.

Not to pick nits... but you mean to say "Needs to be heat-treated after welding". At some point in the process, yes, it's likely to be hardened also, but there's any number of things you can do to that steel to stress relieve or normalize it after it's welded. The trouble with welding a high-carbon steel like that is that the weld IS getting 'heat treated', just not in any way that's consistent with what the user wants it to be. Some is harder'n hell, some is annealed dead soft, some brittle, some very fatigue resistant, others not even a little bit... and so on..

[cj737]

if you go to Jody's YT channel and do a search for 4130 several videos come up, there is 1 from a year ago that may address this "TIG Welding 4130 Chromoly Tubing" it may be good to watch as there has been much debate on this topic.

https://youtu.be/88fBukKg0x4