thanks for the link, checked it out and am now happy that the couple of welds I need to proceed with will be OK mig'd if I pre and post heat. The welds are in a non critical area but It looks like I gotta get ready to tig the rest. thanks Slick
thanks dude, really usefull links, good tips and practical advice - reccommend this link if you want to learn the basic stuff right off. I can weld ok but having the pro's tips etc helps you to dodge some of those little pitfalls. cheers Slick
OK guys I've got the answer now. My understanding at this point is this; Tig with correct filler wire (slightly lower tensile than material to be welded) is best for chrome moly - end of story, it can be welded by other methods but with a comprimise in ultimate weld strength. This forum is the best place to get advice and encouragement for a DIY guy - thanks heaps Slick PS I'll try and get some pics up to show what I'm up to
chromoly is not strange, if you tig with 70s2 no problem, if you are a hobbiest and going to over heat the work piece bc you do not know how to properly tig, you might as well mig weld it, since most people can alot easier than tig and not apply excess heat. If you can not mig weld properly, dont touch it
Geez. This again. From a pro, not a hobbyist: MIG welding Chrome-Moly can be done. Some santioning bodies do not allow MIG welding of Chrome-Moly. However if you choose to do so, the type of wire will depend on the application. ER70S-6 or ER80S-D2 should do with 75/25 mix gas. The key will be your stress relieving after welding. This should be done around 1100 deg F. Use a 900 deg temp crayon or temp stick (Tempil makes some good ones, www.tempil.com) and mark about 3/4" to 1" away from the joint. Use a torch with a neutral flame and move about the joint until the temp mark changes. Do not force-cool the area after weld or stress relieving.
If you put a modern top fuel ch***is in an oven the end result would be twisted more than your average pretzel (unless it was clamped in a rigid fixture). Annealing 4130 weldments is absolutely unnecessary in all but high end aerospace applications and then only when dealing with certain types of parts. Welding 4130 with ER70 or ER 80 mild steel rod makes for a relatively ductile weldment that is more than sufficient for the sort of applications that we are dealing with. Roo
As Roo said, CM is normalized so taht you just weld it up. But do it with tig! The tech guy will gig you and send you home if you mig it. Get rid of those bolts - no point in welding a structure if it is going to be bolted with mystery metal bolts. When you do thru bolting it is proper to weld a sleeve into the tube. You make sleeves for a bolt size by adding an eight inch and getting .058 wall Xmoly, so for 3/8 you'd get a piece of 1/2" X .058 wall - the bolt will be a perfect fit. It is a good idea to make a pad like you have for the thru bolts, just weld'er up. Show us what you are doing at the firewall befor you go too far. What speed/certification are you going for?
Not Hydrogen Embrittlement. What you have is fusion line cracking due to carbides that form at the fusion line and heat affected zone due to heat of the welding. Cast iron is difficult to weld because if the high carbon content.
The metallurgical reason for this is to temper the martensite that is formed when you MIG weld Cr-Mo. That is why in general Cr-Mo is not MIG welded. It has too fast of cooling rate and you get untempered amrtensite in the heat affected zone. Untempered martensite is very hard and brittle. TIG or gas welding has slow enough cooling rate that you do not get martensite to form. Tempering the martensite helps bring back some ductility, although best to avoid forming it in the first place. I am/have been the HAMB metallurgist from way back. Understanding *why* things happen and not just old woves tales is important to help understanding of the root cause why.
I have heard that a good filler rod for welding CR is 17-4 stainless. Has anyone else ever heard of this?
The purpose of a weld is to turn two pieces of metal into one. Physically and metallurgically... 4130 Chrome-moly is much closer to mild steel than stainless in terms of alloy. I've heard this same idea, because the stainless filler "flows" so much better, but it has a much higher chromium content, which as far as I know, does nothing to help the ductility of the weld area. That is going to be your main issue no matter how you weld 4130. I've had the best success (TIG) using uncoated 65,000 tensile mild steel filler (Oxweld or Linde 65). For a welder with limited experience, I would recommend using a MIG, but doing plenty of s**** samples and checking weld flow and penetration until you get the machine right. Then at least it is going to do the same thing every time. DO NOT try to learn how to TIG weld on 4130. Your life may literally depend on it...
OJ I'm building myself a "RaceRod" - I want to have a car that can be driven road legal to the race track have the wheels driven off it and drive it home, looking to get into the 10's at the strip? well that's the aim... plus we have a bunch of events for Hot Rods at speedway tracks - link below. I'm a semiretired dirt track racer that can't let it go, we always used mild steel tube for our cages but this time I thought what the hell save the weight... so now I am going to learn tig - sweet as. I can gas, arc and mig and my buddies tell me if you can do those you can tig. As for the through bolts, they are threaded into sleeves welded top and bottom of the rails. <CITE>www.jalopyjournal.com/forum/showthread.php?t=548347</CITE>
As Roo said, CM is normalized so taht you just weld it up. But do it with tig! The tech guy will gig you and send you home if you mig it. Get rid of those bolts - no point in welding a structure if it is going to be bolted with mystery metal bolts. When you do thru bolting it is proper to weld a sleeve into the tube. You make sleeves for a bolt size by adding an eight inch and getting .058 wall Xmoly, so for 3/8 you'd get a piece of 1/2" X .058 wall - the bolt will be a perfect fit. It is a good idea to make a pad like you have for the thru bolts, just weld'er up. Show us what you are doing at the firewall befor you go too far. What speed/certification are you going for?
Normalization temps from 1" or so on the CM away from the weld explains to me me how a dirt car cage failed around here. I wasn't involved in any of that. I've messed up enough with my known failures and breakdown of failures. Ain't many and I can call out why the few happened.
if tis going to be drag raced you do not have a choice TIG it or you'll never get on the track. I learned to tig on moly, not that bad but you should practice on things that arent going to risk your life though.
Those plates to the frame, MIG with an E70S6 Those Chrome Moly Tubes to the plates. *TIG* E70S2 and you will p*** any NHRA TECH in the country providing the rest of the cage is appropriately installed. And I gotta say YES to the Blind leading the Blind comment. WOW Caging is for protection Don't skip on Safety bubba. I see you got it tacked if you don't have a tig find a local who does...Please. Don't skimp on Safety bubba. Its your life we are talkin about here.
I built MANY off road ch***is out of CM that were MIG welded and the heat treated. Won the Baja 1000 a**** many others and that is a hell of a lot more pounding and violent impacts than anything that these cars will see. It's a matter of using proper rod, technique and post weld treatments. And yes the heat treat is done in a Big ***ed Oven. If you don't know what you are doing, have someone who does do the job, and yes TIG is preferred as it's easier for the Tech Guy to see what has been done and not need a Heat Treat Certificate.
Dragster ch***is don't get heat treated and do just fine. I think the stress of an off road ch***is would be much more punishing to say the least. My buddy uses a tig wire called missle or rocket rod, it is about 5 times as expensive as er70s, the standard tig wire. The missle rod is a bit softer and melts at a lower temp, it has a gold color and is great for welding dis-similar metals too, ie. mild and chromoly. Being abit softer it is more maluable and would give some in impact instead of the moly cracking above the weld. This wire is NOT legal in drag racing, but he uses it for other fab. Here are some examples taken from an offroad buggy he built. The tubing is moly. My buddy has been in the drag racing sport for over 25 years and has built over a dozen FED ch***is and is co owner of one with Tony Waters. On a side note i went to a sand rail show a few years back and saw several $100,000.00 moly sand cars wire fed. Some had tiged suspension parts but not all. Also Dirt Works sold ch***is back a few years with moly front halfs, wire fed. TIG is the way, but i thing wirefeed is OK in the right condition.
Just a note: brazing is not gas welding. Brazing is Brazing, using bronze or br*** rod, usually. Gas welding is welding, simply with gas. No flux involved, and no br***. I don't want to sound like a jack-off, but there's no use in confusing people by universally applying technical terms. With regards to the initial question, I'd go for TIG or gas weld. Gas particularly does away with the need to preheat the Moly, hence the reason it is still the preferred method of aircraft structural repairs on tube structures.
You can stick weld it lo-hidrogen. I used to work for a job shop that made molly steering box mounts and fender braces for Peter Built off road and the prints called for low hydrogen stick welding or low-hy core wire as the procedure. If you use low hydrogen core wire there is no reason in the world that it could not be wire welded. The old race ch***is builders thought it had to be gas welded. that works and is an easy process if you can gas weld. Use good filler not coat hanger welds.
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