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TIG weld cracking issues, carbon steel - heat cracking?

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  • TIG weld cracking issues, carbon steel - heat cracking?

    Background on my problem: I weld this one particular part at work pretty frequently. It's an L-shaped bracket with a hole in it where a pin goes through it at a right angle. The bracket is maybe 3/16" thick and the pin is about 1" in diameter. Both pieces are carbon steel, nothing special. Both pieces are adequately cleaned. The process is TIG welding with a Miller Syncrowave 250. The equipment is functioning just fine. Using ER70S fill rod.

    We have cracking issues sometimes with the welds on these. It shows up immediately. You have to make three beads to complete the weld, and it almost always shows up in the third and final bead, sometimes the second one. You'll just wind up with a crack that runs the length of about half the weld. The only thing that seems to help it is to turn down the amps on the welder, but sometimes even if you turn it way down (we are usually welding around 200A) and you are at 175A it still cracks. If you run over it a second time with more fill rod it's fine.

    The weird thing is some nights it's not an issue at all, and sometimes it seems to happen on every fifth or sixth part. Anyone have some suggestions on what's going on here? It slows me down getting work done, because I have to pause after every part and look at it and be real positive it doesn't have a crack rather than just pulling it out of the jig, tossing it on the table, and moving on to the next piece. I could be turning out a lot more of these things if I knew we had the problem licked.

    Thanks to all in advance,
    Tom

  • #2
    maybe this will help

    http://www.lincolnelectric.com/en-us...ldcracking.pdf

    Comment


    • #3
      Could the pin be leadloy or sulfurized?

      Ask for the real material alloys so you can choose a more appropriate filler.

      Comment


      • #4
        Thanks Ed and shovelon. Ed, that article is GREAT! I will see if I can find out what the makeup of the steel is that we're welding, but the article pointed out several things that I can try that might be the problem or contributing to it.

        Last night for some reason I started thinking about torch angle and how getting lazy with that might be affecting things, so I got real careful about it and that seemed to help. I also noticed "high speed passes" might be a problem, and I can definitely get moving fast at times, so I'll look out for that. Plus, I see that welding straight down on a right-angle joint can be a problem, and the jig kind of makes you want to weld that way just because it's easier to clear obstructions and move quickly if you do. Last, it looks like turning down the amperage might be something to consider, although I'm not sure how low I can go and still get appropriate penetration. My day guy (who is essentially my welding boss and has several years of experience) tells me to try and not go below 200A, but sometimes that's the only thing I can do to lessen or stop the problem. I do notice that my welds are concave, and I didn't know that was incorrect on that type of joint. I've noticed before when backing off the amps that the weld does become more convex.

        Thanks for the information,
        Tom

        Comment


        • #5
          Not sure if this applies but one thing you didn't mention is whether the piece you are welding the L-shape to is also 3/16" thick. Even if both pieces are the same material you can still get cracking if one of the pieces has a significantly greater mass than the other at the weld site. In that situation the two pieces will cool at different rates putting stress on the weld.

          Comment


          • #6
            Matrix, yes, the pin that gets welded into the hole in the L-bracket is 1" in diameter approx, so there's a significant difference there. It seems I've got several things working against me here and it may just come down to careful moderation of heat and my welding technique.

            Comment


            • #7
              OK, for some reason I thought the pin was removable and the bracket was welded to something else. Like the braket was an anchor for something that attached with a pin.
              The pin is solid or hollow?
              Are you doing a full-penetration weld (like a category D) or just a fillet?
              Either way how much gap is there?

              Comment


              • #8
                No, sorry, the pin is welded onto the bracket. I shouldn't call it a pin I guess, that's just the slang in the shop. It is actually a shaft that is welded onto the bracket. It is solid steel. The gap between the parts is minimal, but it is not a snug fit. I would have to guess at it, and I'd say somewhere less than 1/16" at its widest.

                Could you please explain a "category D" weld? I don't have much in the way of formal training, so those terms escape me lots of times.

                Comment


                • #9
                  That's an ASME designation. It might refer to the kind of weld you're doing where one part goes through another but it is specific to a beveled preparation where the 3/16 Pl is beveled to get full penetration to the pin. However it could also be category C if it's a fillet weld with no bevel. Pipe welds are typically category B, a slip-on flange would be category C, a straight flat plate beveled butt joint would be category A. I have a pdf drawing but I'm not sure how to post it here. The ASME (American Society of Mechanical Engineers) weld type designations have nothing to do with fit-up or position. It's just a way to describe the kind of joint but it gives more detail than "butt joint", "lap joint", etc.

                  Comment


                  • #10
                    TIG weld cracking issues, carbon steel - heat cracking?

                    One thing to consider, hot cracking, can come from welding at to high temp along with to fast travel speed. If your weld is also concave this is a possibility.
                    Welding to hot is just as bad as to cold. Just because u weld at high amps doesn't assure proper penetration. It comes as much or more from proper technique with correct amps. Watch & work the front edge of puddle to achieve good penetration, adjust travel speed to allow rear of puddle to fill in for proper weld thickness.
                    Also welding down is difficult to acquire good penetration & weld thickness.
                    A good weld is not just laying a bead. It comes from allot of thought & preparation i.e. Metal thickness, metal type, type of joint, angle, filler metal, type of gas, amps,torch angle, travel speed etc. Put it all together with a little practice & your welds will be great.
                    Just a thought, hope it helps.
                    ....a couple pictures may be worth a thousand words....

                    Comment

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