Filler metal selection for welding mild steel and 4130 tube

Howdy Folks! I was looking for some advice on an upcoming project. I will be restoring a 1940's vintage Harley-Davidson springer front fork that has been extended using Ford Model A radius rods. This was common practice during the first "long chopper" craze of the late 1960's-early 1970's. Problem is that back in those days, people from every walk of life was doing this, so buying a vintage piece like I did was a crapshoot, as far as whether or not you were going to end up with the forks snapping at the weld point at 70MPH on the Interstate. The piece that I bought is extended about 10" over stock, using the aformentioned radius rods for the rear fork, and some unknown tubing (by the looks, some cheap, welded-seam hotroll) for the front fork. I'll be replacing the front tubes with seamless DOM 4130 in an upcoming thread. Today, I was looking for advice on filler rod for this project. I'll be using my 250EX, which is the GREATEST welder ever made, IMHO (and until I get the new 255EXT:D that is!). Anyway, I came across the link below. A good, SHORT read.

http://www.aws.org/wj/apr03/AWfeature.html

It explains filler selection, and the possible tensile strength, depending on dilution level achieved with the parent metal. I was educated and surprised at how strong a joint can be made with the right conditions. I recommend that anyone interested in welding tubing give it a look. Take ya' 5 minutes. Good Luck!!

Use ER70S6 filler and just weld it as if it were standard low carbon steel.
If the weldment was all 4130, and you were going to heat treat it fully afterwards, then 4130 filler could be used.

I almost always use Er70s6 when doing chromo work. The softer weld is good for transportation applications like cars and bikes. Its usually a good bet to give up some tensile strength to gain a lot of ductility. With cars and bikes you want joints that fail to bend, and not to snap and shear. You can always add a gusset or fish tab to increase strength at the weld. Also, the extra vibration resistance from a softer filler metal will help make your work last longer.
Things to keep in mind when welding chromoly is that its more heat shock sensitive than regular steels, you need to be gentler with heating and chilling the weld puddle, move slower, and taper off the amperage and increase your post gas to lower your chances of your weld cracking while it cools.

ER70S2 is the usual TIG rod; 70S6 is a normal MIG wire. You don't need the extra silicon for TIG:) S/F....Ken M

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Originally Posted by EchoSixMike

ER70S2 is the usual TIG rod; 70S6 is a normal MIG wire. You don't need the extra silicon for TIG:) S/F....Ken M

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A lot of people use S6 for 4130 because it wets out better from other properties of the silicon besides deoxidizing. In some places it works quite well. I also prefer S2, but mainly because I think it handles out of position welds better. You will find plenty of people that swear by one or the other. Just like some people use 70S2 MIG wire for clean metal welding.

s2 vs s6 isn't much of a difference. each welder will find what works better for them in different situations. s6 is what i got used to and got good with because almost everything i do has to deal with widely varying metal thicknesses, and i often get stuck with dissimilar alloys being welded together. The wet-out properties and deoxidizing properties of s6 work better for me.
As far as makeup go, s6 does have like twice the silicon and manganese of s2... but that's only 1% of the total makeup. s2 is 97% iron, and s6 is 96% iron, so for all mechanical intents and purposes they are equal, it's pretty much just the 'puddle characteristics' that differ.

This is good info. Seems personal preferences differ in similar applications. I'll be looking to some of you when I get to this project. My intent was to get the publication available to those who may not have seen it. Thanks for the input.

One thing to consider, and you may want to call some of the high end front end builders, is the mechanical stresses that will be involved, anything you can do to better the front end should be done. I'm looking at rebuilding (replacing a leg) on a girder, first stop after welding is to get it out for heat treatment. I want any internal stresses, embrittlement, etc. gone before I put a few hundred pounds of dynamic weight on a funky angle connecting to something that will vibrate like hell and have opposing forces applied to it in high cyclic rates.

Ductility is king for cages. I think it would be wise for suspension components also. Of course, YMMV.

http://www.youtube.com/watch?v=ytSrEggjz1A

S/F....Ken M

I picked up some S6 for the framework on a buggy project coming up, and a bunch of S2 for just general welding stuff.

Has anyone used 309? Jody says that it's his "go to" rod when he's unsure of the parent metal. In the case of a 6 decade old motorcycle part, I have NO IDEA what alloy they originally used.

309 is really only used if part of the base material is ss. i use s2 for 4130 cages, mainly because there are many points where you connect the cage to the frame of the car which is usually lower grade mild steel.