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Thread: Low penetration TIG welding?

  1. #1
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    Low penetration TIG welding?

    Hey gang,


    I recently bought my first TIG machine and had a question about my specific usage:


    I'm a knife maker and I want to use the TIG to make fusion welds to seal up the seams while making multi-layer stacks of steel. As I'm using this to make an air-tight environment for forge welding (heating up to 2300F and smashing the layers into one homogenous billet), would I be correct in thinking that low voltage fusion welding would be enough to just seal the seams between layers of steel without penetrating too deep?


    Thanks!

    P.S. Still waiting for my machine to come in, otherwise I'd just be experimenting myself.

  2. #2
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    Re: Low penetration TIG welding?

    Sure. Especially if your new machine comes with a good programmable high speed DC pulse. Jody's rule of 30 should do the trick. Otherwise Miller's default high speed pulse setting is very good for the wetting weld you want to tie layers with.
    Weld like a "WELDOR", not a wel-"DERR"
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  3. #3
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    Re: Low penetration TIG welding?

    Great, thanks! Thanks for pointing me to Jody's rule too.

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    Re: Low penetration TIG welding?

    Quote Originally Posted by brick View Post
    Great, thanks! Thanks for pointing me to Jody's rule too.
    That would be Jody Collier, Welding tips and Tricks.
    Weld like a "WELDOR", not a wel-"DERR"
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  5. #5
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    Re: Low penetration TIG welding?

    Quote Originally Posted by brick View Post
    I'm a knife maker and I want to use the TIG to make fusion welds to seal up the seams while making multi-layer stacks of steel. As I'm using this to make an air-tight environment for forge welding (heating up to 2300F and smashing the layers into one homogenous billet), would I be correct in thinking that low voltage fusion welding would be enough to just seal the seams between layers of steel without penetrating too deep?
    A couple of points of clarification. Technically pretty much all welding is fusion welding as you're fusing two things together. Welding like you're describing is autogenous welding where you don't add filler to the puddle. It's one of those things some folks will argue about even though we normally know what's meant when mentioned.

    Second, it wouldn't be low voltage, it would be low amperage. With TIG your set the machine based on the amps you want and the voltage varies with arc length (and probably other factors).

    As far as the welding itself, you're really going to have to try and see what happens. Since you'll be welding two different metals in most cases, and they're largely going to be a high carbon tool steel or alloy steel (unless you're doing a San Mei) things can get tricky. There are times when welds without filler are more likely to crack and once you get to setting the welds they might fail...especially if you're using a press or power hammer. If you're worried about contaminating the billet with low carbon filler rod you could buy filler rod made for welding tool steels or alloy steels.
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  6. #6
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    Re: Low penetration TIG welding?

    One of the challenges of welding higher-carbon tool steels is that when you melt the substrate, some of the carbon in it dissolves into the weld deposit, effectively transforming the weld nugget from a low-carbon deposit into a medium- or high-carbon deposit. This can cause problems when the workpiece sucks heat out of the weld deposit real fast, effectively quenching it and making it harder than the hammers of he!!. The internal stresses can cause cracking of the weld.

    To guard against this, the Lincoln book "Metals and How to Weld Them" recommends what it calls "25-20" filler for high-carbon tool steels...a filler of about 25% Cr and 20% Ni ... which is essentially 310 tig filler. I guess that even if the carbon migrates out of the substrate into the weld puddle, the high nickel content adds a lot of ductility and helps prevent cracking.

    Not sure what this would do to your billet when you hammer it out at the forge...I'm also not sure that the cracking that you would normally get in the weld will necessarily be a bad thing, since you'll be bringing everything back up to welding temperature and fusing it together again when you take it to the power hammer....

  7. #7
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    Re: Low penetration TIG welding?

    Great info above. Also take into consideration the size of your tungsten. I enjoy doing very thin materials with .040 tungsten and 5-20 amps depending on what I'm doing. You can experiment with grind angles of the tungsten too. Tig welding has perhaps the most variable options in welding. I just wish I were better at it. Good Luck.
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  8. #8
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    Re: Low penetration TIG welding?

    Thanks all for the clarifications, education, and tips!

    I'm not too worried about the welds failing since they only need to keep air from getting in-between the seams until I give it a first pass on my forging press. After the first press, my high carbon steels will be forge welded and my dinky autogenous welds will have served their purpose. I forgot to mention that these low-pen welds are only to cover the seams and that I have stronger welds at the corners of the billet to keep it from falling apart before I can forge it.

    Thanks again!

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