[ajlskater1]

Hey guys got 8 weld up 8 4 link bars to a mild steel bung. The tubing is 1/4 is wall 4130. I am going to put a bevel on the tubing. What preheat would you guys recommend for the chromoly? And should I tack then preheat or am I better off preheating then tacking and welding?

[Poland308]

I would tack then preheat.

[ajlskater1]

Do you know what preheat to use?

[Poland308]

Not for sure but it's probably around 500 deg f.

[Otto Nobedder]

Most high-chrome steels are pre-heated to 350-375. If a second pass is required, interpass temperature should not exceed 400. General guidelines, as I've not done the specific weld you asked about.

Steve S

[Sandow]

Isn't 4130 considered a low alloy steel?

-Sandow

[ajlskater1]

Thanks guys that is the info I was looking for. It's so hard to find preheat temps for some reason.
Wish there was a chart out there. I will have to do 2 passes so I will watch interpass temp. Would you guys recommend a post heat or just let it cool down on its own?

[Sandow]

My charts say preheat to 300 to 400F and post welding heat treat at 1275 to 1400F. Welding to mild, I'm not sure the post heat treatment makes much of a difference though.

If it is a critical part, I'd use a temp stick: http://www.amazon.com/Markal-Thermomelt ... temp+stick

-Sandow

[ajlskater1]

Ya I went and got a 300 temp stick and 400 temp stick so I don't go over interpass temp, cause I will have to do 2 passes. They are 4 link bars, not horribly critical but still want to do it right. My concern about post heated that hot is distorting the threads. I disassembled the Hiem joint so I didn't wreck them with the preheat but still kinda worried about the adopter threads. Think I will find a bolt with the same threads and screw that in during the preheat and weld. I think I will just let them cool on their own.

[dave powelson]

Ya I went and got a 300 temp stick and 400 temp stick so I don't go over interpass temp, cause I will have to do 2 passes. They are 4 link bars, not horribly critical but still want to do it right. My concern about post heated that hot is distorting the threads. I disassembled the Hiem joint so I didn't wreck them with the preheat but still kinda worried about the adopter threads. Think I will find a bolt with the same threads and screw that in during the preheat and weld. I think I will just let them cool on their own.

"kinda worried about the adopter threads.
Think I will find a bolt with the same threads and screw that in during the preheat and weld."

That's a great way to permanently seize the bolt to the threads....not every time,
dependent on thread engagement, heat expansion and platings/coatings...but quite often.

Leave threaded ID-open. Chase with tap and lube after.

[big gear head]

Have you considered drilling a few holes in the sides of the tubing and adding some plug welds? A local chassis builder told me that he has had some problems with the weld breaking on this type of joint, but if he adds a few plug welds through the sides then he has no problems. I did this on the track bar on my car just to add a little safety to it.

[Sandow]

Ya I went and got a 300 temp stick and 400 temp stick so I don't go over interpass temp, cause I will have to do 2 passes. They are 4 link bars, not horribly critical but still want to do it right. My concern about post heated that hot is distorting the threads. I disassembled the Hiem joint so I didn't wreck them with the preheat but still kinda worried about the adopter threads. Think I will find a bolt with the same threads and screw that in during the preheat and weld. I think I will just let them cool on their own.

Yeah, the post welding heat treatment usually seems like voodoo. From what I've read, in thin material it is outright bad due to carbon depletion. From the knife making I've done, the uselessness of the decarb layer is obvious so I believe that notion. In thicker material, that isn't going to happen due to the limits on the diffusion rate so the stress relief starts to win out for overall strength. There seems to be some consensus that over 1/8, do the heat treating.

You may or may not be able to limit thread distortion by putting a grade 5 or 8 bolt in there. I'm guessing you'll still need to chase the threads with a tap though. What I would really recommend is some copper based thread lube/anti-seize cause that bolt will be an absolutute bitch to get out otherwise lol

Curious... What did you decide on for filler?

-Sandow

[Rick_H]

Have you considered drilling a few holes in the sides of the tubing and adding some plug welds? A local chassis builder told me that he has had some problems with the weld breaking on this type of joint, but if he adds a few plug welds through the sides then he has no problems. I did this on the track bar on my car just to add a little safety to it.

I am also partial to this idea and have done it with success on my own drag car stuff as well. Definitely do not thread a bolt in the end then weld....

[ajlskater1]

Ok thanks guys, I guess I won't be threading a bolt in it from the sounds of it. I am going to weld it with er 70s2, since there will already be dilution from the mild steel bungs. I beveled the ends of the tube, so that I can get more weld throat, I will do a root pass and come back over the top with a fill. I am going to try and get them all done tonight. I'll post pictures when they are done. I will have to go buy a tap. Thanks for all the advise guys. You guys on the forums are awesome !

[ajlskater1]

Got them all done tonight. I fitted the adapter with a 1/16 gap, kinda like a socket weld, so there wouldn't be any shrinkage stress cracks. The first one didn't go great at first, the root cracked on me, so I had to grind it out and do it over. I figured out that dipping fast on the root works much better and I got no cracks. At first I tried to space the dips out further and that's when it cracked, think I was getting to much dilution. After the root I did 2 fill passes and then a weave cover. Next time I won't do a 45 degree bevel on the end of the tube it took a lot of fill, mayb like a 20 degree instead. But I think they turned out pretty good for never having welded thick chromoly before. I let the part cool back down under 400 each pass. Took a long time. I think it took like 45 minutes a part. Had a adapter on both ends. Was a lot of fun and hope to get more on this kind of work. Where do you guys find preheat charts?

[Poland308]

The waiting for the interpass temp is killer. Looks like it went good.

[Oscar]

Some info I've collected regarding 4130 chromoly:

https://drive.google.com/folderview?id= ... VFIN3ZHZjg