4130 welding, need advice 3

[400fnSport]

OK, I'm constructing an ATV frame out of 4130 cromolly. My question is all I have is a MIG welder, (Solar 2175) and have never done anything like this before with this type of alloy. I was told for a good weld with 4130, I need to TIG, but I don't have and can't afford a TIG just for this application. But I was told I could MIG with 100% argon and er70s-6 or es70-s5 wire. (I don't know which one of those I should use) But is this my only option, or could I oxy-acetelene it using a 4130 rod? I don't know which one is better, and don't really know the process of how to weld using a oxy-acetelene thorch. but I need the welds to be strong of course, but all stress points will be gusset. Any advice is appreciated.

 

[jeffita]

boo1,
Right you are about ER80S-D2.
I brought the filler rod question to a prominent member of the NHRA/SFI chassis committee a while back and brought up that i had read about a new AWS standard that will state just what you had posted.
I was told to continue using ER70s-2.(4130 tig)
So in the drag race world thats what we use.
As a side note, In all my time at Mcdonnell Douglas, Northrop,Boeing, Allied Signal,(yes i made the rounds doing the layoff shuffle)as a tig weldor, we used nothing but 4130 filler wire with a pre and post weld heat operation.

Hopefully we didnt scare 400fn sport away with all of this.

 

[Metalguy]

Ah,my first post! First, since you (400fnSport) are a beginning welder, be advised that it is very easy to make good-appearing MIG (GMAW) welds which are only "fused" on one side. The arc must be directed into BOTH sides. I would recommend that you weld a 4130 frame using oxy-fuel, AFTER someone shows you how, with emphasis on how to adjust the flame to avoid oxidation or carburization.

The slow cooling of oxy-fuel welds (because you heat up a lot more tubing) should avoid the problem of having a crack-prone heat-affected-zone (HAZ), which is really a base-metal problem rather than a weld metal one. For a new welder, TIG (GTAW) would be my 2nd choice, but you have ruled that out.

 

[MASSEY]

Did someone say they use coathangers for welding rod?? Isn't all that burning plastic and smoke bad for your lunges and eyes?? How could you see what you are doing???

 

[patdaly]

Massey, works just fine, the Lacquer coating burns away long before you get much smoke. As I said above, I have never tried using it with GTAW, but it works beautifully for OXY.

 

[MASSEY]

patdaly,

Please pardon my sick sense of humor--I was referring to the new plastic coat hangars--not the good ol' metal ones.

Hey, if it works for you - more power to you. I commend your resourcefullness.

 

[patdaly]

LOL, I need more coffee in the mornings, sorry, it zoomed right by!
Thks.

 

[harvwest]

I,m building a motorcycle chassis with 4130 and after much consideration,am using oxy/acetylene.Beyond the expense of tig,it is also much more difficult to get into tight spaces,and it requires post heat treatment with the torch anyway.This is the one area that had me worried,I have no gas welding experience.I bought a Meco midget torch,It weighs only 6 ounces,is very precise,and gets into the nooks and crannies easily.My very first joint I got 100% penetration,and what I consider,a nice looking weld.For an atv chassis,as long as your tubing is reasonably thick,you shouldn,t need to worry about things being strong enough.A rule of thumb with motorcycle chassis is,if you can,t cut it with your snips it,s too thick.Another advantage of the torch is that you can go as slowly as you like and really see what,s happening at the weld.For a beginning welder such as myself,perfect.Check out TM technologies for more.

 

[nousakmj]

I don't know if this thread is dead or not, but I'm going to comment anyhow. My vantage point is that of a metallurgist and welding engineer, so I'll be more of a purist than apparently any of the other respondents.

4130 is a heat-treatable medium carbon steel with nominally 0.30% carbon, 1.00% chromium, and 0.20% molybdenum. The material can be provided with a pretty wide range of properties, all dependent on the heat-treated condition. Annealed 4130 has a yield strength around 65 ksi and a tensile strength of about 80 ksi. Mormalized 4130 will run around 65 ksi yield and 100 ksi tensile. Quenched from 1575 deg F in water and tempered at 900 deg F, the material goes to 160 ksi yield and 170 ksi tensile.

If you are welding such a material and need to match the strength of heat-treated tubing, then you should use a 4130 filler metal and postweld heat treat (i.e. quench and temper) the weldment.

If you want to undermatch the filler metal to the base metal for ductility's sake, then an ER70S-2 or -6 will work, as will ER80S-D2 (or even ER90S-D2) for GMAW. The ER70S-2 or -6 are carbon steel filler metals. The -D2 filler metals are alloyed with manganese and molybdenum.

If you are trying to match composition, then an ER80S-B2 is the ticket -- it has a nominal composition of 1.25% chromium and 0.50% modlybdenum.

You have to decide what you are trying to accomplish here. Just because a bunch of railheads used a cheap carbon steel filler metal for years, doesn't mean it was the right material. By the way, if you want to use coat hangers, you'll be using the approximate equivalent of ER70S-3.

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com

 

[nousakmj]

Just for giggles, a few more comments. It is hard to weld small diameter tubing using GMAW. The skills required to manipulate the electrode tip properly would usually require some level of automation. As noted by others, TIG (GTAW) or oxy-acetylene (OFW) would be the choices. Both require skill, but OFW is more operator dependent than GTAW. For this application, TIG should be your ticket.

Regarding filler metal designations, you need to go to the American Welding Society web site and start looking up the filler metal specs. AWS A-5.20 covers carbon steel electrodes for the FCAW process. The suffix for these wires does indicate the flux type, whether it is gas- or self-shielded, and the arc transfer characteristics (spray versus globular). AWS A-5.29 covers low-alloy steel electrodes for the FCAW process. Here the suffix denotes the chemical composition "family" of the wire. "A" is for carbon - molybdenum wire, "B" is for chromium - molybdenum, "Ni" is for nickel, "D" is for manganese - molybdenum, and "K" is for all others (but mostly nickel - chromium - molybdenum). The number in the suffix differentiates the amount of alloy within the "family". There are flux and shielding gas designators also, but they appear before the suffix (and after the "T", which stands for "tubular&quot.

As for using 1020 tubing, there is nothing wrong with it as long as the loads applied don't exceed the material's strength. 1020 comes in various conditions, hot rolled (40 yield & 60 tensile), cold rolled (50 yield & 65 tensile), hot rolled and quenched and tempered (45 yield & 70 tensile), as rolled (50 yield & 70 tensile), normalized ( 50 yield & 70 tensile), and annealed (50 yield & 75 tensile). The strengths are approximate and given in ksi. What you should see is that 1020 is considerably weaker than 4130.

Last, but not least, pipeingg needs to brush up a little on his metallurgy. While chromium is indeed added for corrosion resistance, in low-alloy steels it is intended to improve the strength of the material at elevated temperatures. Molybdenum is also added to increase corrosion resistance (particularly to pitting) and creep resistance, but creep resistance has nothing to do with this application. Creep resistance is the ability of a material to resist growth upon prolonged exposure to elevated temperatures, and unless you plan on driving with your frame above 800 deg F (what a hot seat!) for extended periods of time, it doesn't apply.

If you really want to increase the longevity of your frame, then fatigue properties are of interest. In which case you should be looking at nickel alloyed materials (or even, for your case, nickel-alloyed filler metals). That's why you see 4340 alloy steel used so much in the aircraft industry.

Lotsa luck.

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com

 

[Metalguy]

The reason 4340 (and the better 300M) steels are used for aircraft are because the parts are so large. They require deep hardening steels, and that's the main reason all that alloy (Ni, Cr & Mo) are in there.

An ATV frame isn't anywhere near thick enough to require such deep hardening, unless it's big enough to take a few families out 4-wheelin'!