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Thread: Welding Question! Welding 4130 Steel to Other Metal

  1. #1
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    Welding Question! Welding 4130 Steel to Other Metal

    I am part of the FSAE team at Western University (London Ontario). In previous years the entire car was a 4130 profile-cut steel tube space frame, which I helped to weld. In 2015 we switched to a hybrid chassis design - the front is a carbon-fiber sandwich panel monocoque, and the rear is still a cromoly space frame. We use a motorcycle engine (Honda CBR600F4i) mounted to the space frame with 8 separate mounts, 4 on either side. The mounts are tophat style slugs placed into the cromoly tubing. Typically we use a mild steel to make the tophats and then weld the parts to the 4130 tubing using a soft filler such as ER70s-2.
    This year one of our experienced team members made the tophats out of a peice of stock he found on our material rack. He complained of some of the parts being very hard to part off on the lathe, and the stock showed some really wavy marks where the parting tool was. The material had a very shiny finish to it (i will post some pics shortly) and didn’t look like regular mild steel. I took the stock to a machinist who told me it is not regular steel, it is definitely something harder like 4130 or 4140.
    The same guy welded these parts to the cromoly tubing to complete the engine mounts. He used unibraze s-6 (ER70s-6) MiG wire as filler since the gaps were very small. I know he did not preheat the tubes or the tophats before welding. These are photos of the finished welds:





    You can see some slag on the weld beads. I think this is relatively normal. I am more concerned about the possibility of these mounts cracking. They are very highly loaded in the car (they hold the engine in place, and the engine drives the wheels via chain drive) and are exposed to large amounts of vibration as well. I know in my experience welding hard materials (without preheat) is that welds can crack. I am very concerned that these welds will crack and cause our engine to start rattling around. Usually we use mild steel for the tophat material and weld it with ER70s-2 as the filler and we have never had an engine mount failure. This year, with our unknown tophat material (could be 4130 or 4140) I think there is a significant chance of failure.

    I have a couple of questions:
    1. Knowing that the tophat material is not mild steel and is probably a higher carbon steel, would you be concerned with this weld failing? This is a highly loaded area experiencing lots of vibration.
    2. If we need to redo the weld, how far down the 4130 tube should we cut to ensure that there is no remaining material from the original weld?
    3. If we redo the weld with ER70s-2 and mild steel top hats will it be more likely to crack since we have alredy put a heat cycle through the cro-moly?

    I appreciate you making it this far and any help you can offer. I have some experience welding and fabricating but I would rather not learn this lesson the hard way. This is our car on the line and the stakes are high!
    www.uwoformularacing.com
    University of Western Ontario... or Western University depending on who you ask

  2. #2
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    I can't offer much as I don't have experience with this issue, but if you are truly concerned you could just make some test pieces and fatigue test them. Also, if you are concerned about welding 4130 to 4130, why wouldn't you be concerned about welding 4130 to mild?
    Jay

    UoW FSAE '07-'09

  3. #3
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    Thanks for the reply. My main concern is if it's a harder material (ie. 4140) that would require special pre or post weld processing. I know that 4130 to mild and 4130 to 4130 typically does not cause us any problems, but I dont have any experience with 4130 to 4140. I do have experience with welding tool steels/other harder steels having them crack at the welds. I was just looking for some input on this issue to know if anyone has ever worked with this metal (possibly 4140).
    www.uwoformularacing.com
    University of Western Ontario... or Western University depending on who you ask

  4. #4
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    Were they clean before you welded? I've seen welds like that just from very oil-impregnated metal.

    I have a feeling that as long as you anneal it (like you might a 4130-4130 joint) you won't have any cracking issues, but that has no basis in fact.
    Jim
    "Old guy #1" at UCONN Racing

  5. #5
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    Leif,

    Ahh, welding discussions...!!!

    The BAD NEWS.
    A universal truism of welding is that if you ask one hundred highly experienced welders how to do a job, then you get one hundred different answers, most of them diametrically opposed to all the other answers. (<- Hard to believe that is even possible, but it is!)

    The GOOD NEWS.
    FSAE is one of the least demanding ordeals any weld is going to have to survive. Lots of much tougher jobs out there.

    The BAD NEWS.
    Neverthless, many FSAEers manage to fail dismally in the competitions, because of failed welds. (Ahh..., what Auckland might have achieved at the recent Oz-comp, if not for the failure of a teeny-weeny little weld! Well, they actually got 4th place, so not so dismal...)

    The GOOD NEWS.
    Learning how to do good welds is quite easy (see below).

    But first some welding-waffle.
    ~o0o~

    "4130" is a moderately strong steel that was developed ~100 years ago, primarily to be cheap and easy to weld, so it could be used on things like bicycle frames and those new-fangled flyin' machines. The "41" signifies it has just enough of the alloys needed to make it cheap/easy-to-weld/strongish. The "30" means it has roughly 0.30% carbon mixed in there. This makes it a "medium carbon steel" (ie. between ~0.2 to 0.5%), so it can be strengthened by heating/quenching++.

    "4140" is essentially the same stuff as 4130, just with a pinch more carbon thrown in. Very little difference. Probably a bigger difference between 4130s from different suppliers, than between 4130/40 from the same supplier. So, if whatever you were doing to weld 4130 worked OK, then expect very little difference when doing same with 4140.

    But (!), if you picked up a piece of, say, 1060 (no special alloys, but a bucket-load of carbon in there, with 0.60% in the "high" range), then you might have some problems.

    Nevertheless, I have welded 1060+, 9xxx-series "hi-silicon" spring-steels, and other bizarre Fe-alloys, quite "successfully" (<-see definition below). Quite easy, really. The "Weld-All" approach (<- that was a brand name) is to use austenitic "stainless-steel" welding rods. You mentioned that your welder used Unibraze MIG wire, so something like the Unibraze-308L would probably work well-enough for any of the 41xx steels.
    ~o0o~

    So, what is the definition of a "successful" weld?

    Answer: One that NEVER BREAKS!!!

    In short:
    1. Put the welds in the lesser-stressed regions of the weldment, NOT in the most highly-stressed areas.
    2. Make the weld physically BIGGER than the parent metal either side of it. So, crank up the amps, and pour that molten metal in! (This approach might have given Auckland an overall victory.)
    3. If the weldment breaks somewhere other than the weld, then that is someone else's problem. (Stupid Design Engineers, they can't expect the welder to solve all their problems!)

    I thought you might have got the second one wrong when you said "... since the gaps were very small", but your pics look OK. Leave the dainty-little-welds to the show-ponies, and crank up those amps...
    ~o0o~

    And how do you learn how to do successful welds?

    Answer: TEST THEM!!!

    Use one of the tubes in your images as a test-piece. Find the highest grade bolt in your workshop that will fit in the tophat-hole, and bolt the test-piece to a solid lump of steel, say a 1" thick steel-plate. Clamp steel-plate in the biggest vice in your workshop. Take a BIG hammer, or a heavy steel bar (say 1"+ round x 2'+ long), and bash away at the tube. You must keep going until either the bolt, or the weld, or the tube, parts company from the vice/big-steel-plate, and the end of the tube is lying on the floor.

    If weld fails, then BAD WELD!

    If anything else fails, then GOOD WELD!

    Too easy!

    Z
    Last edited by Z; 01-19-2016 at 10:08 PM.

  6. #6
    Quote Originally Posted by Z View Post
    And how do you learn how to do successful welds?

    Answer: TEST THEM!!!

    Use one of the tubes in your images as a test-piece. Find the highest grade bolt in your workshop that will fit in the tophat-hole, and bolt the test-piece to a solid lump of steel, say a 1" thick steel-plate. Clamp steel-plate in the biggest vice in your workshop. Take a BIG hammer, or a heavy steel bar (say 1"+ round x 2'+ long), and bash away at the tube. You must keep going until either the bolt, or the weld, or the tube, parts company from the vice/big-steel-plate, and the end of the tube is lying on the floor.

    If weld fails, then BAD WELD!

    If anything else fails, then GOOD WELD!

    Too easy!

    Z
    Z has the right idea here.

    Get a big hammer and give 'er hell, man.

    4130 to 4140 isn't a very big deal at all. If you check some mild suppliers you can notice that their carbon content varies even greater than that for baseline "mild steel". You can cut two pieces of steel from the same sheet and they may have up to about 25 counts difference in carbon content. Here's one fine example: 1006-1026. 20 counts difference right there.

    http://www.mcmaster.com/#standard-steel-sheets/=10rnyuy

    So, don't worry too much, you're probably fine but can prove it and document it for the design event.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  7. #7
    To my eye, you have several problems going on.

    1) There should NEVER be slag or visible impurities on the surface of a properly performed tig weld, ever. Period.
    2) Looks like insufficient shielding gas coverage - the color bands outside of the weld area should be farther from the bead. The bronze/gold color over several beads means they were either not properly covered (too little gas flow, too small of a gas nozzle, electrode protruding too far from the nozzle), possibly improper shielding gas. The bead should be very close to silver in color - some discoloration where you start or stop depending on pre- and post-flow of the shielding gas is ok.
    3) Improper cleaning - that's where your flaky bead surface is coming from, it looks like the mill scale wasn't cleaned prior to welding. Especially with alloy steel which often has a light black oxide coating this is absolutely critical. You need to spend time with a metal wire brush or Scotchbrite to get down to clean shiny steel at least 1/2 in. away from your joint, then wipe with acetone or IPA just before welding - that alone will help a lot. Use only something that will not remove material - avoid sand paper, flap disc wheels, grinding wheels, etc.

    ER70S-6 should be fine for that combination.

    The fact that the stock was difficult to machine might indicate it's not what you thought it was - then all bets are off anyway.




    These are all 4130 tubing with ER70-S2 filler, and all tig welded.

    See how much farther from the joint the color bands of oxidization are here:




    Bead coloration:





    Tubes are 4130, the body where the sill plate is welded down is mild steel, and the filler was all ER70S-2:

    _______________________________________

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

  8. #8
    Wait wait. I reread the post. I thought the first time through you were certain it was 4130 or 4140. Apologies.


    If you can present a piece of the tophat that was machined before being welded in, especially the top face, it might help identify it. Some grades of steel have certain characteristics that make the identifiable like tool steels and 4340.
    If it was difficult to part, but easier to machine otherwise, it might have been some stainless steel. Stainless is a cruel mistress that likes to work harden.
    See if there is a color on the end of the stock that was used as well.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  9. #9
    Leif,

    Check the stock from which the top hats were made. If it is non-magnetic, then it is certainly neither mild steel nor 4130/4140 - most probably one of the "300 series" stainless steels

  10. #10
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    Hi everyone,
    Thanks very much for all the replies. I've gotten bogged down with work so I haven't been able to respond.

    On my end, I spoke to a number of professors at my school and also got a few conflicting answers. However, one discussion I had with a materials prof allowed me to finally get some sleep and feel better about the situation. We discussed TTT diagrams and how the cooling rate affects the microstructure of the metal after welding. The TTT diagram shows the temperature of the material on the y-axis, the time to cool on the x-axis, and the phase transitions as functions of slope. A plot for 4130 is shown below:



    I have placed the red marker on the y-axis indicating around where the temperature of the material after the weld puddle cools. Based on experience, it takes the welded area over a minute, generally around 3 minutes to cool to room temperature which is the bottom of the graph. The areas marked with Ms and Mf are the points where martensite forms in the material, and since martensite is the hard and brittle phase of iron it is likely this that causes the brittle fracture. This also explains why it is important to pre and post-heat welds. If the area where you are welding is right next to a cold area (think a block that wasnt pre-heated and most of it is at room temperature), this area will have a very large temperature gradient and the local rate of cooling will be much greater there. The weld would be most likely to fail in that spot.

    Compare the 4130 TTT diagram with the diagram of 4340:



    This diagram shows that 4340 has phase transitions that occur much later than the 4130, meaning that Martensite formation will occur sooner with a faster rate of cooling, and Austenite or pearlite formation requires slower cooling rates to form. This is why 4340 is regarded as a poorly weldable steel as it requires more attention to proper heat treatment. We have reason to believe that the steel we used for the engine mounts is NOT 4340 as we have a labelled piece of stock in the shop and it appears much different (outer surface brighter, machine surfaces shinier... very accurate I know). Therefore since the material used is either the same as the chassis tubing (4130) or slightly different (4140) I feel much more confident in the parts.

    Before speaking to my professor I did not really understand why metals can become brittle during the weld process, I had only seen it myself when welding on tool steels. In the past when TiG welding tool steel I had not preheated the material and the welds cracked almost immediately. The TTT diagram explanation allowed me to get a better understanding of the microstructure transitions and put some numbers to all of the 'shop talk' that exists.


    Quote Originally Posted by Z View Post

    And how do you learn how to do successful welds?

    Answer: TEST THEM!!!

    Use one of the tubes in your images as a test-piece. Find the highest grade bolt in your workshop that will fit in the tophat-hole, and bolt the test-piece to a solid lump of steel, say a 1" thick steel-plate. Clamp steel-plate in the biggest vice in your workshop. Take a BIG hammer, or a heavy steel bar (say 1"+ round x 2'+ long), and bash away at the tube. You must keep going until either the bolt, or the weld, or the tube, parts company from the vice/big-steel-plate, and the end of the tube is lying on the floor.

    If weld fails, then BAD WELD!

    If anything else fails, then GOOD WELD!

    Too easy!

    Z
    I actually did this, but on a smaller scale. I put the tube in the vise and beat on it a bit with a hammer. Since we didn't have any extra pieces made I didn't want to destroy the part for the car so I went a little easy. Nonetheless, they didnt fail. That experiment, coupled with the TTT diagram explanation gave me a bit more faith in the parts.

    Quote Originally Posted by Drew Price View Post
    To my eye, you have several problems going on.

    1) There should NEVER be slag or visible impurities on the surface of a properly performed tig weld, ever. Period.
    2) Looks like insufficient shielding gas coverage - the color bands outside of the weld area should be farther from the bead. The bronze/gold color over several beads means they were either not properly covered (too little gas flow, too small of a gas nozzle, electrode protruding too far from the nozzle), possibly improper shielding gas. The bead should be very close to silver in color - some discoloration where you start or stop depending on pre- and post-flow of the shielding gas is ok.
    3) Improper cleaning - that's where your flaky bead surface is coming from, it looks like the mill scale wasn't cleaned prior to welding. Especially with alloy steel which often has a light black oxide coating this is absolutely critical. You need to spend time with a metal wire brush or Scotchbrite to get down to clean shiny steel at least 1/2 in. away from your joint, then wipe with acetone or IPA just before welding - that alone will help a lot. Use only something that will not remove material - avoid sand paper, flap disc wheels, grinding wheels, etc.

    ER70S-6 should be fine for that combination.
    The welds are not perfect, that is for sure. It was likely a shielding gas issue. We replaced the bottle and have been welding the rest of the frame (4130 with ER70S-2 filler) with no issues (other than a healthy amount of heat input!). We are definitely paying more attention to the cleaning and preparation of the tubes. As Z said, ask 100 different welders a welding question and you will get 100 different answers. I know the welds are not perfect, but based on experience this type of low heat TiG welding on thin parts is strong enough for the application.

    Thanks to all who replied and sorry that it took me so long to get to this. Between myself and the rest of the team we learned a good deal through this process and am glad that it occurred. Happy building!
    Last edited by leif; 02-06-2016 at 01:46 PM.
    www.uwoformularacing.com
    University of Western Ontario... or Western University depending on who you ask

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