[Chris64]

OK, I'm building some A-arms for a Quad out of 4130 (1" .120" wall). This will be my first experience with welding 4130 though. Needless to say, I'll be running a few practice beads on scrap.

Anyway, I was told by the "guy" who worked at the welding store to get 4130 filler (ER4130) which didn't seem right to me since I've never used the same metal for filler ever before. Here's what people say:

* ER4130 if you're going to heat treat it
* ER70S-2 if you're not going to heat treat it is fine
* ER80S-D2 For higher strenth, less ductile welds (?err?)

Nobody really directly states that ER4130 is wrong to use if you don't heat-treat it, they simply indicate that "if no heat-treat, then it's not necessary."

Can anyone shed any light on this for me? I don't intend to heat treat the parts but obviously strength is important. Many years ago I read that you ideally want small welds to prevent from changing the hardness of the surrounding area too much.

[One of Many]

I am no welder for the most part, but consider the application. 4130 is an oil hardening material. As long as it is allowed to air cool, it should return the its base condition. If the part required heat treating and you wanted consistent properties throughout the weld and part, then by all means, use the base material that will respond in like fashion to the heat treat process.

As with many things, you cannot have something for nothing in terms of material physics. As the ultimate tensile goes up, the ductility or ability to deform under sustained stress and fatigue goes down. The balance should be with modes of failure given what could result. It isn't so bad with things show signs at the start of a failing joint. High strength-Low ductility may not give you that chance if\until it just snaps at the least inopportune moment.

You have 2 options with no heat treat, so.....which is more economical or readily available?

DC

[Geof]

I am not a welder by trade but I do weld and worked for a while in a place that had certified welders. I picked up a bit of information from them and this is my understanding of the metallurgy behind 'what people say'.

When you weld you get a heat affected zone surrounding the weld. At the weld the filler material and the parent material both are above the melting point and the temperature diminishes away from the weld. Because the weld area is small and the parent material is big the molten area gets quenched by the heat soaking away into the larger volume of cooler metal. This quenching effect varies with distance from the weld so you don't know what the state of the metal is; it will probably be somewhat hardened closer to the weld but not as hard further away. It certainly has all manner of internal stresses due to uneven cooling.

When you are going to heat treat you will be bringing all the material to the same metallurgical condition so you can use the same material for filler as the parent material. Actually you should use the same material so you have a homgeneous structure.

But if you are not heat treating having a hardenable material as the filler is not a good idea. If there are regions around the weld that vary in hardness and stength when the structure is stressed it will not respond the same way in all places. Stresses tend to concentrat in the zones between harder and softer material and this can cause stress cracks to form and ultimate failure of the joint. Often times if you look at a failed weld joint it has cracked slightly away from the weld.

The way to try and combat this situation of hardened zones around the weld is to use a filler rod that does not harden as much; generally a lower carbon steel would be used. In the weld zone this melts and mixes with the parent material so the metal in the molten zone does not harden as much when it cools. Because it is not as hard it is more ductile and when a stress is applied the greater ductility allows the stress concentrations to be relaxed a bit by plastic deformation. This does unavoidably reduce the maximum strength in the weld region but because it has lowered the concentrated stresses it can make a stronger weld overall. Certainly a weld that even without heat treatment is much less likely to cause stress cracking.

You are building suspension arms? I strongly suggest you get advice from a certified welder or consult with a heat treatment company. At the very least you need to get you welds normalized. You probably do not want them cracking.

[tsutt]

I am welder built over a dozen aircraft fuselages a couple have been crashed , no weld failures. Use er-70-6 or better mild. the weld will remain ductile so it does'nt crack.An aircraft manufacterer use 4130 on fuselage for a few years and have all kinds of cracking problems. Todd

[greg b]

On motor cycle frames we mucked around with over the years we used chrome moly tubing for good strength and flexability without breaking.There are quite a few ways of welding this material ,however i dont recall ever using 4130 for that application only for pins /axles /machined brackets.

[Chris64]

Thanks for the info everyone. I'm speculating but I'm 99% sure that the aftermarket companies who manufacture these parts don't heat treat them so they must be using something other than 4130 filler. I only bought a pound of it so it wasn't too much of a waste (although it is about 3x the price of everything else). I'll look into the ER70 options and try to narrow it down from there. Thanks again.

[GisMo]

Go with ER70s or ER80s-D2

You don't want to mess with heat treating and 4130 filler will leave you with a relatively brittle weld joint. Some recommend waving a rose bud around your joints after welding to stress relieve. Bring it to a dark red and let it air cool. IMO, not necessary, especially in thinner wall tubing. Anyways, you want that ductility in the joint and you get it with those fillers without any post treatments. welding chromoly is very similar to welding mild steel. I've welded a few chromoly buggy chassis' and suspensions together with er70 and er80 no post treatments and all are still in one piece. Dial your machine right and make some sound welds and you'll be in good shape.

in my experience, you'll probably have better luck finding er70s on the shelf of the welding stores. if you can't find the er80s-d2, no big deal. go with er70s

[diesel dave]

Do not use 4130 filler, and definitely do not heat treat, makes for very brittle welds. I am a welder by trade and do a lot of cages, A arms etc. I use er70s6 and s2 is I am out of s6.