Welds tearing?

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What causes a weld/welds to tear?  Not on the edges but towards the middle of the weld.   2G, Back side of test plate, and root pass ( front side ) is near flawless, ties in fully and almost sticks out.I am frustrated because I do not know what to do.  My instructors have watched me lay beads.  Watched me do the whole test plate, and not found any thing to cause issues.  They even watched the backside for the "white" swirl... and tieing in...    After 6 or 7 of these, they are at a loss and do not know what to tell me, and they do not think that there is anything I am doing wrong.  I personally have changed up speed... tried smaller weave, tried larger weave... tried 1/8 rod, went back to 3/32...  tried more amps... tried less amps... tried different machines...  just at a loss.. any input is a help... Moving on to "open root" for now and will come back to 2GOh yeah, this is GTAW ( tig )  7018  (ER 70S-2 I believe?)Thanks in Advance.. off to class fellas... thanks again...  I will try and get a few pics.. if I can...
Reply:Smokeshadow,There's some missing information from your original post, and without it I don't think we can be of much help.Can I assume you're welding mild steel, based on the fact you're using ER70-S2 for filler metal?How thick is the base metal, plate or pipe, and what are the dimensions for the joint?  Root opening?  Root Face?  Bevel Angle? Etc.You mention welding in 2G.  Please confirm that the joint runs horizontally, just to make sure we're all talking about the same thing.What are the equipment settings you're using?  What shielding Gas?You mention weaving to form the weld bead.  Are you walking the cup or freehand welding?  What's your work and travel angle?The only thing I can guess, based on the info in your first post, is...A tear running parallel to the weld joint, dead center of the bead sounds like a defect caused by thermal stress.  As the weld joint cools, it shrinks.  If the base metal is tightly constrained, the stress created in the joint could cause the metal to fail...but this is all guesswork.I'm not familiar with this happening with steel, but I have seen it happen with aluminum.How do you have the test pieces fixtured?  Are both halves of the joint rigidly mounted?Is the crack occurring once all welding is complete, or during welding of the joint?  i.e. is the weld unzipping behind you as you progress along the joint?
Reply:I will second that more information is needed. Pictures of the joint pre weld post weld and the failed coupon, would do a lot as well.I have some ideas and will withhold them till more information is at hand.JIMMY
Reply:quenching would make it brittle...thats all i can say with the info statedSooo like said above more information please.6G zirconium 702 GTAW 2" xxheavy6G P.E.D. carbon steel GTAW 2" xxheavy3G titanium Gr. 2 - Gr. 7 GTAW up to 3/4" 3G 316L stainless GTAW up to 1" 3G carbon steel GTAW up to 1" 3G Hastalloy GTAW up to 3/4"1G tantalum GTAW up to .060"
Reply:First bead is walking cup...  rest are free hand...Bevel is horizontal/ 2G... 3/8 mild steel... They changed the way of doing things this semester, before you can do a test plate you have to fully weld a 2x2 angle.  Well, on a 3/32 filler rod, that is going to take a while... but maybe by the end of next class I can finish it out.. but I believe I may have a possible solution... I was hold the torch perpendicular to the metal,  but I think holding it parallel like I was while welding up the piece of angle... and the beads seem to have slightly more penetration...  but as always more input is greatly appreciated..
Reply:thats how i walk the cup haha i put a big gas lens and cup on so i can stick the tungsten out furhter and keep good gas coverage =)but good luck though6G zirconium 702 GTAW 2" xxheavy6G P.E.D. carbon steel GTAW 2" xxheavy3G titanium Gr. 2 - Gr. 7 GTAW up to 3/4" 3G 316L stainless GTAW up to 1" 3G carbon steel GTAW up to 1" 3G Hastalloy GTAW up to 3/4"1G tantalum GTAW up to .060"
Reply:Forgot to mention, that last semester they had us reusing old plates that someone had not finished.  So we had to cut out or grind out the old welds and try to reuse the plate..  I think contamination ( sp? ) was possible.