HREW vs. DOM dent resistance

[Weasel]

And why would that be. You do not have to tig weld chromoly, mig will work just as well.

 

[Captain Ron]

...
mig will work just as well.

Don't do it Weasel. ER80S-D2, ER70S-2 and -6 work with TIG only because the base material "mixes" during puddle flow and filler add. With MIG, you don't get this to the nessesary extent.

If you get a CroMo frame with big, ugly, crappy welds on it, take it back. TIG or not. If your chassis builder tries to fill a 1/16" gap in CroMo, fire him.

--ron

 

[luvrox]

And why would that be. You do not have to tig weld chromoly, mig will work just as well.

Of course you have to consider I learned this all in the sixties and I may be a little behind the times. First you will need a gas shield to make the perfict weld on 4130. A Mini tank and regulators aprox 60 lb. Then comes the wire issue, you will do best with a role of er70s. To stop the stress crack issue it's best to stress relieve the weld area by bringing the weld to around 1100 degees then feathering it out. That will require a a pair of oxy acetylene tanks and regulators. At aprox. 90 lbs.

Gas 60 lb.
Welder & wire and gun 40 lb.
Oxy / Acetylene 90 lb.

Or you could go with plan B and hook a couple of batteries together with a tube of 1310 and have your dom rig back in action with what? Maby about ten extra lbs.

 

[Captain Ron]

...
To stop the stress crack issue it's best to stress relieve the weld area by bringing the weld to around 1100 degees then feathering it out.
...

Not nessesary on anything .120" thick or less. In no way proven, but my gut feeling is that blowing it during this proceedure contributes to lamellar failure. Crack prone joints are usually simply a case of a poor fit, leading to excessive filler material addition and inadequate base material mixing.

--ron

 

[luvrox]

Not nessesary on anything .120" thick or less. In no way proven, but my gut feeling is that blowing it during this proceedure contributes to lamellar failure. Crack prone joints are usually simply a case of a poor fit, leading to excessive filler material addition and inadequate base material mixing.

--ron

Score one for Ron.

 

[Weasel]

Don't do it Weasel. ER80S-D2, ER70S-2 and -6 work with TIG only because the base material "mixes" during puddle flow and filler add. With MIG, you don't get this to the nessesary extent.

If you get a CroMo frame with big, ugly, crappy welds on it, take it back. TIG or not. If your chassis builder tries to fill a 1/16" gap in CroMo, fire him.

--ron

This is the frist I've heard of the "mixing" effect. Is this a proven welding method or just a idea. Not being a smart ass just asking. I have not heard fo this from any of the ASME or AWS procedures/info I have read.

The dnager with welding any low alloy high hardenable steel is the formation of maternsite. This is a highly brittle crystal structure that leads to cold cracks. The way to help this is to slow the cooling rate. This is where pre-heating comes into play, but preheat may or may-not be needed, you would have to consult the RPI tables for this. However I do know that you can weld 1/4" 4130 and the cooling rate will be slow enough that martensite is not formed. So for the tubing thicknesses we use the cooling rate should not be an issue.

I know what I said one the filler issue before, of using ER70-S2 but after learning a bit more about welding I think you can use 4130 filler (or not filler with TIG) without resulting in brittle welds. As long as you don't have a travel speed to high you should also be able to avoid any hot cracks, from liquid films.

However with 4340 it is much more hardenable and much harder to weld as just about any combination of welding on this steel will result on maternsite, so preheat is a must and care must be taken.

I guess I'm not sure what your getting at with the gas issue? All of our Mig and Tig machines use gas shields for the welds.

So what am I missing?

 

[Weasel]

Not nessesary on anything .120" thick or less. In no way proven, but my gut feeling is that blowing it during this proceedure contributes to lamellar failure. Crack prone joints are usually simply a case of a poor fit, leading to excessive filler material addition and inadequate base material mixing.

--ron

Actaully there are two forms of cracks that form in welds. Hot and Cold.

Hot cracks are due to "liquid films" and strains. Liquid films therioes are when the weld is cooling the liquid metal is pulled back from between the grain boundaries, if the liquid cannot fill the area fast enough then a hot crack forms.

Cold Cracks are from three different causes, hydrogen, thermal stresses, or the formation of martensite. See above for the martensite issues.

Filler material listed above doesn't have issues with martensite unless your using a high hardenable steel. Base metal mixing I don't think has much to do with it, the metal is melted and flows together.

 

[luvrox]

I guess I'm not sure what your getting at with the gas issue? All of our Mig and Tig machines use gas shields for the welds.
So what am I missing?

To make it simple, how well will those banks of bottles fit in the back of your XJ to do field repairs?

 

[Dan Fredrickson]

I say fillet braze the whole thing and get on with your life......:laugh3:

However, I am a believer in the fact that the same materials in the same thickness results in the same strength. But, with that in mind you can successfully use HREW in most applications where you can control where the welded seam is, in bent materials I prefer DOM because you do not need to be so aware of the seam location and the effect of the bend on the seam itself, which BTW, is welded perfectly by a computer in most cases.

Also, when buying tubeing be aware of too good of a deal, many dealers will sell you factory seconds with uneven wall thicknesses and never mention the fact you are getting such a good price because the material is a Factory Second. And another however, a "second" may be just the ticket in less important areas.

 

[Weasel]

To make it simple, how well will those banks of bottles fit in the back of your XJ to do field repairs?

Do it right and you don't need field repairs. But yeah bottles would be a pain.