chromemoly welding

[dirtmonster17]

im want to know if there is a special technique to weld moly?im in school to learn how to weld,my instructors did not know if there was a special way.i would like to know for the reason the reason im going to school is to build race cars.thanks

[TheRealSpinner]

lots of people will agree that the way to weld chromoly is to TIG weld it, but mild steel filler. the reason being: chromoly is a hard material. when you weld it, it has a tendency to destroy these properties and cause weak points. if you MIG it, you will most likely overheat the material (further away from the weld too). by TIGing it, you can control the heat better and direct it exactly where you want.
the reason for using mild steel filler is that because chromoly is so hard, the weakest part will be the material near the weld (not at it). if the filler is just as hard as the rest of the material and doesn't allow the piece to give at all. the piece will likely tear at the weak point. by using mild steel, there is less rigidity at the joint which allows everything else to be rigid and still allow enough give in the piece (less stress on the other material). the mild steel filler will be plenty strong to hold up.

[M1.30-'06]

Your welding instructors dont know the proper procedures???

[JD in Socal]

Do a search and you will find enough material to keep you reading for days.


JD

[Billet Benny]

lots of people will agree that the way to weld chromoly is to TIG weld it, but mild steel filler. the reason being: chromoly is a hard material.

I disagree.. It can be hard, but it depends on the condition it's in. It is also harder than a mild steel, but not near as hard as other higher carbon steels or alloys.

if you MIG it, you will most likely overheat the material (further away from the weld too).

100% wrong. The trouble with mig is exactly the opposite.

if the filler is just as hard as the rest of the material and doesn't allow the piece to give at all.

the problem is the failure of the weld itself when welded with matching filler and left as welded. it has nothing to do with "giving"

the piece will likely tear at the weak point. by using mild steel, there is less rigidity at the joint which allows everything else to be rigid and still allow enough give in the piece (less stress on the other material). the mild steel filler will be plenty strong to hold up.

wrong. no matter what filler you use there is no difference in rigidity of the joint or structure. with mild steel filler the failure point should end up being at the edge of the haz. with matching filler your weld itself becomes very impact and crack sensitive and is normally your abnormally weak point.


Use the search button and 4130 and/or my name and you will find all you ever want to read.

[JD in Socal]

I disagree..

100% wrong....

wrong. no matter what filler you use there is no difference in rigidity of the joint... ...with matching filler your weld itself becomes very impact and crack sensitive and is normally your abnormally weak point.

All right, Mr. Smarty-pants. I thought Spinner made good points and got the idea across. This isn't welding college here, and the general concepts are what is important, which he addressed pretty well.

You say he's wrong about chromoly being hard, then acknowledge that it's harder than mild steel. You say he's wrong in suggesting a chromoly joint welded with matching filler is "hard" or more "rigid", yet you go on to say that such a joint is "very impact and crack sensitive and is normally your abnormally weak point".

Spinner, I think you provided good info in the context of the question.

Dirt Monster, the search button is your friend. You can read more than you ever wanted to know about chromoly welding, and Benny can review and correct all questionable terminology.

JD

[shadetreewelder]

I will try to stay clear of any conflicts in this post.

Primarily race car frames are welded with GTAW, most for cosmetics, racers like pretty welds. Cr-Mo Tube (typically 4130) can be welded with GMAW or GTAW processes and be equally strong. There was a nice article in the PowerClick for GMAW of 4130. However when welding 4130 and similar alloys you should weld with 80S-D2 filler to more closely match the alloy properties. If you are welding higher carbon content alloy 4140 and such a little preheat would be recommended.

I have both 80S-D2 in cut lengths for GTAW and 0.035" for GMAW.

With any steel alloy, the higher the carbon the higher the preheat.

[Billet Benny]

All right, Mr. Smarty-pants. I thought Spinner made good points and got the idea across. This isn't welding college here, and the general concepts are what is important, which he addressed pretty well.

The things he said are misleading and not true.. I'm not a smarty-pants, but I am on a mission to spread the truth about materials and welding when it comes to the points I am experienced with and study. I've tried my best to post this info whenever I can in order to help people make sound decisions based on facts and material properties. I think we just went over a lot of this info and terminology a week or so ago. I'm only trying to help because there is so much misinformation that seems to float around including places you shouldn't see it.

You say he's wrong about chromoly being hard, then acknowledge that it's harder than mild steel.

I said it depends.. It can be softer than mild steel in the annealed condition, but harder in a normalized or quenched and tempered condition. It's not its hardness per se that causes problems, rather its hardenabillity. I'll touch on this in a minute. But saying you must take caution when welding because it's hard as a blanket statement isn't true.

You say he's wrong in suggesting a chromoly joint welded with matching filler is "hard" or more "rigid", yet you go on to say that such a joint is "very impact and crack sensitive and is normally your abnormally weak point".

I did not say that a joint welded with matching filler is more rigid.. This is not true.. No matter what steel or steel alloy filler you use the joint will not be more rigid. This again is a function of a steel's modulus of elasticity which is the same for all steels from 1008 to steel alloys. The weld itself (not the original base metal) will turn out to be hard as a by product which now will present a problem. What happens is you get a weld mixture composed of lots of carbon and alloys which has high hardenability. The cooling rate from welding is too fast to maintain ductility in the weld and the residual stresses created cause two problems. The weld itself may actually crack on its own due to too much stress (but this is avoided w/ preheat) and it also becomes a very impact sensitive zone which is rarely good for what 4130 parts are used for. This micro structure problem can only be properly corrected with heat treatment and tempering in a very closesly temperature and time controlled device.

Using lower carbon steel fillers works as welded because it gets away from the problems of having a weld bead with high hardenability that cools fast. It now won't crack upon cooling and will show ductility upon impact and stress. You could end up with a weld that with stands all this with a matching filler, but it'd be a crap shoot and not repeatable. The weakened zone will be at the edge of the haz and normally a fully welded joint with mild steel filler is going to be stronger than that anyways yet offers a lot more forgiveness in the welding process.. I hope that clears it up a little.

[JD in Socal]

I hope that clears it up a little.

Yes it does.

I'm not sure it significantly changes the message that Dirt monster got from the Spinner (feel free to disagree), but it is definitely more technically accurate. Thanks for clarifying your points.

Oh, and I was just kidding about the smarty-pants thing.


JD

[dirtmonster17]

thanks guys i just need a little bit more info on where to find more info.

[dirtmonster17]

used welders

any one near tennessee have any used welders that they would like to get rid of?tig,mig,stick does not matter as long as the price is right.

[TheRealSpinner]

I appreciate the knowledge and knowhow that members like Benny have, but personally, I like answers like the one I gave; pretty concise, without a lot of technicality. In the end, I believe that both the answers (mine and Benny's) were very similar.
I would like to say that I did attacked by the WAY that Benny corrected my answer, but I am glad that there are people on this forum with knowledge to do so.

[Billet Benny]

I appreciate the knowledge and knowhow that members like Benny have, but personally, I like answers like the one I gave; pretty concise, without a lot of technicality. In the end, I believe that both the answers (mine and Benny's) were very similar.
I would like to say that I did attacked by the WAY that Benny corrected my answer, but I am glad that there are people on this forum with knowledge to do so.

No way no how was I trying to attack you.. I agree it probably sounded harsh but that's only in an effort to get my point across, definitely not to attack you. Cool?

What I thought you were getting at was that matching filler is a bad idea because the welded joint becomes rigid and won't give therefore causing the surrounding tube to fail. That is not correct information and that's what I was trying to refute. If that's not what you meant, then I just understood it wrong. That's where I thought our two explanations differ. Using a mild steel filler does NOT give the joint more "give" thus creating less stress on the surrounding tube. That's not how it works. That's the point I was attempting to make.

Also on the mig welding part. To be quick with it. Mig inherently has the smallest haz of the common arc welding processes which makes it touchy for 4130 because it allows the deposited weld and haz to cool quickly which we know is a bad bad thing. This is simply fixed with some proper preheating to slow the cooling rate to more mimic that of the tig process.

Think about it this way. We know oxy-fuel is a very accepted and sound process for 4130. We also know it is a very high heat input welding process. As a by product of this the welds deposited via oxy-fuel cool slowly (relatively speaking).

We also know mig, tig, and oxy are similar in that they create a weld by melting base metal and adding filler.

Now IF haz sizes in order from smallest to largest went like this (which they don't): tig - mig - oxy.. why would it make sense that oxy fuel is so good and mig is not, when we know tig is well accepted and used?

The actual haz sizes for the processes from smallest to largest go like this: mig - tig - oxy.. This is really why oxy and tig are such good processes for 4130. Because both tig and oxy have enough heat input per adequate weld size to slow cooling down enough to not form an overly quenched weld.

This is probably the most important part of welding 4130, not cooling the weld overly fast. Tig and oxy are processes that just lend themselves to this without any conscious effort so they fit the bill well.

4130 is not magic, just different and a bit tempermental.

Just wanted to touch on that.

[Silverback]

Primarily race car frames are welded with GTAW, most for cosmetics, racers like pretty welds. Cr-Mo Tube (typically 4130) can be welded with GMAW or GTAW processes and be equally strong. There was a nice article in the PowerClick for GMAW of 4130. However when welding 4130 and similar alloys you should weld with 80S-D2 filler to more closely match the alloy properties. If you are welding higher carbon content alloy 4140 and such a little preheat would be recommended.

I have both 80S-D2 in cut lengths for GTAW and 0.035" for GMAW.

Huh… what 4130 are you welding with a mig on a race car chassis? I don’t know of any rules that allow MIG welding on 4130, even though for the life of me I don’t know what the advantage of it is anyway, and I realize that it welds fine with a MIG (that’s not really the issue, I believe that this and a lot of the rules around using 4130 in chassis are basically short sighted, or just basically incorrect from a technical/safety perspective).

What I thought you were getting at was that matching filler is a bad idea because the welded joint becomes rigid and won't give therefore causing the surrounding tube to fail. That is not correct information and that's what I was trying to refute.

I agree with most if not all of your statements in this thread but you seem to leave out the reason why not to use 4130 filler on 4130 structures. Besides the fact that there is not strength/rigidity advantage, there is the disadvantage that if you get that joint just a little too hot it will have a tendency to crack, which it will not do with mild steel. The only time it really makes sense to weld 4130 with a comparable filler is if you’re actually going to have the parts heat treated after you’re done (which I would argue is the only time it really makes sense to use 4130 to start with).

Getting back to welding it… I’m not sure if ER80S-… filler is really that big a deal anyway, since yes, it is closer in strength to the 4130 (and to 1020, and especially 1026 which is designed for tubular structures), but the fillet/thicker section of the actual weld makes the minor difference in yield strength irrelevant, since the welded area if done correctly will be larger and stronger anyway.

Also on the mig welding part. To be quick with it. Mig inherently has the smallest haz of the common arc welding processes which makes it touchy for 4130 because it allows the deposited weld and haz to cool quickly which we know is a bad bad thing. This is simply fixed with some proper preheating to slow the cooling rate to more mimic that of the tig process.

This probably is my biggest issue with welding 4130 structures that will not be heat treated… I don’t know what increasing the HAZ does to improve your 4130 joint? It just gives you a bigger brittle area. Done properly, none of the welding processes should cause any cracking, and unless you have literally DAYS for the thing to sit at >1200& in a temperature controlled situation none of them will cool slowely enough to prevent a brittle area around the weld.

I do love how most people want to convince you that you can create a smaller HAZ with TIG… not at all unless you don’t get the same penetration as with the MIG…

[Buzz Job]

im want to know if there is a special technique to weld moly?im in school to learn how to weld,my instructors did not know if there was a special way.i would like to know for the reason the reason im going to school is to build race cars.thanks

If you want to learn to weld tubing cromoly or mild steel, I’d start with mild first and learn the process of fitting then welding as the two are related to achieve good results.
A properly notched tube is a start to a good weld. And then try to weld the notched tubes. A simple tee will get you started. Keep adding tubes to your existing tee. And if you got what it takes work it from there.

Cromoly welds like mild steel but it has the potential to get harder and that presents other problems that you can learn a bought once you get the basic fitting and welding
That is a subject your teacher should be able to address?
.
By far the best way to weld tight tube structures where constant repositioning and lots of small weld segments are common is TIG.
Mig is acceptable on larger open areas with long weld segments.

Making structures with steel take a lot more than just knowing how to weld, the hardest part for me is getting it all to fit together with a great fit. That will assure a once it gets welded together it ends up with little distortion and strong.
Good luck with building race cars you can do it.