Due to very low hydrogen, are mig welds stronger.

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I googled about hydrogen in welds, and read that mig welding normally has very low hydrogen levels in the weld.By comparison the information said that an excellent (low) hydrogen level for a MMA weld with low hydrogen rods would be four times that of a normal mig weld. I'm comparing gas mig welding, not flux core where the flux gets you back to higher hydrogen levels.Assuming both welds are done properly, with similar filler material, good fusion, penetration, etc then doesn't this mean that mig is generally stronger. This goes against what I generally hear about arc welds being stronger, and some jobs even specifying arc welding and NOT mig welding.I've migged some joints under quite high restraint (excavator bucket ripping out tree stumps, curling the bucket like a lever to snap roots until 3000psi hydraulic relief valve kicks in) and they've never even shown a crack anywhere.Keith.
Reply:Well that is the reason there is flux on the rods in stick welding and fluxcore. Gas shielding in MIG is fine so long as all of the factors are appropriate. So any wind whatsoever will affect your gas coverage on the weld and thus the inclusion of H and O into the weld. Stick doesnt suffer from that because the flux is vaporized and floats on top of the weld to sheild it until it is chipped off. Ditto for fluxcore. However, it does require more labor and cleaning. Also with stick you can weld some sincerely thick metal with a low cost rig. The rig to one pass 1" steel with mig would be massive and beyond the reach of most small companies and certainly individuals. So assuming you dont blow through the metal (since stick is really strong) you can probably do a better weld in more conditions with stick than MIG. Assuming weather cooperates and you have low wind one the weld, you can do a great job with MIG. I hate to say "it depends" but ... in all reality ... it does.
Reply:So say that your inside and all condition are optimial.Not considering the cost of the machine just the end results.In a single pas what would be strunger if both machines were comparable in size?
Reply:I have a Lincoln LN-130 DC only stick welder and I just bought a Linconl 180 Dual mig.
Reply:Originally Posted by Ironhead1983So say that your inside and all condition are optimial.Not considering the cost of the machine just the end results.In a single pas what would be strunger if both machines were comparable in size?
Reply:Thanks YORZAXT
Reply:I think any real world weldor that has done a lot of mig and stick will tell you that a 7018 is a much stronger weld than a mig weld even with E70 wire. I don't know why but I know it's true.
Reply:They aren't stronger, they are tougher.  Low hydrogen welds will absorb more energy in a Charpy Imapct Test.We do a lot of dual shield welding where I work.  It can be frustrating tacking with dual shield because you sometimes can't simply break the tacks with a hammer, the welds bend.
Reply:Thanks for the input everyone.Yorzaxt, I know quite intimately about the effects of wind on a gas mig weld, and it's the reason I'm focusing my practice on my stick welding a lot. I have a 330 amp 3 phase mig which I've done most of my heavier fabrication jobs with, but doing things outside at times has given me a weld comprised more of air bubbles than metal. One minute the weld is going great then a gust of wind comes along and instant chocolate aero bar lookalike.However my question was if both welds are done properly..........so by that I mean optimal and proper conditions for the welds. Joint prep, cleanliness, etc (and zero wind ) I'm not really asking which one is better in all circumstances, just which weld would be stronger if all the conditions were optimal for each weld. The reason I'm asking is that if I'm doing a job in my workshop and I want maximum strength, which weld wins strength wise.The electrode in stick welding actually does have a gas contaminant and that is the hydrogen itself which is in the flux and gets into the weld. That gets back to the info I got off Google which said that a stick weld with the lowest hydrogen level possible would still have 4 times the diffused hydrogen in the weld that a mig weld would.Bob, I hear you. I'm soon to embark on my world of 7018 stick welding and quite a few people love the way they weld too. Just need to try and find out why they are stronger than mig now.76GMC1500, you've pricked up my ears with that one. I was pondering today about asking why low hydrogen electrode welds are tougher. In another thread someone said tensile strength isn't everything and the toughness is a big factor. So do you think mig welds may have a similar tensile strength but not the ductility that a 7018 stick weld would. I'd love to know why a 7018 weld is tougher if say the electrode material is the same. I've heard some say 7018 welds are more ductile and others say they are tougher, but I'm not sure of the exact definition of each. I wonder if toughness is a mixture of tensile strength and how much it can "flex" (ductility ?).By the way what is dual sheild. Is it flux cored mig with sheiling gas ?
Reply:If you take GMAW in short circuit process compared to stick and both welds are done under ideal conditions then they should be equal if the welder is equally skilled in both, generally. Now there starts to become a difference once the steel thickness increases then the limited heat input of GMAW short circuit becomes a limiting factor compared to stick. If you look at the voltages that each processes uses you will see where the difference in heat input a long with the slower travel speed favors stick welding.  Now if you start looking into other CV wire feed processes such as GMAW-S, FCAW, FCAW-G the you start to use higher voltages then you would in GMAW short circuit.
Reply:Strength is a measure of how hard you can pull on something before it fails.  Ductility is a measure of how far something can bend before it fails.  Toughness is a measure of how much energy something can absorb before it fails.When materials are tested, first they are placed in  device that pulls them to failure.  The amount of force required per square inch of original diameter (the specimen will lose diameter and neck down as it is pulled) to cause permanent deformation is the yield strength.  The amount of force required break the piece is the tensile strength.  The tensile strength is lower than the ultimate strength which is the peak strength of the material before significant necking down occurs which reduces the cross section diameter.Ductility is the measure of how far a material can deflect before failure.  Ductile materials will tend to neck down more before failure than brittle materials during a tensile test.  The difference between the ultimate strength and tensile strength will be much higher with ductile materialsToughness is typically measured with a Charpy Impact Test.  A specimen is prepared with a weakening notch ground in the center.  One end is held in a vise while the other end is struck with a pendulum.  The height the pendulum swings after the strike is recorded.  A brittle material will absorb less energy during the strike and the pendulum will swing through more easily and record a higher height  Tougher materials will undergo more plastic deformation before failure and the easiest way to see this is to try to line up the fracture after a failure.  A ductile material will deform greatly before failure and the parts will never line up like original again.The Charpy test works well for comparing different steels because they all share the same modulus of elasticity which refers to how far they bend relative to their tensile strength.  It would be difficult to make comparisons of steel to aluminum in a Charpy test.When you buy welding electrodes the 60 or 70 in the name denotes the strength.  7018 will produce a minimum strength of 70ksi.  ER70-whater will produce the same.  But, know that these are minimums.  Even 6011 welds, 60ksi minimum, will typically be well above 70ksi in the real world.  But 6011 welds suffer from hydrogen embrittlement and will never be as tough as a low hydrogen electrode.  Now, MIG being inherently low hydrogen should have very similar properties to 7018 and to say one is tougher or stronger would be incorrect.  In the field, there may be fewer issues with 7018 because it is less sensitive to conditions.And for dual shield, yes it is a flux cored wire with a CO2 gas shield.  It typically runs as a spray transfer process which makes it ideal for situations where you need to stop and start the arc frequently.  Being spray a spray transfer process, the deposition rate is very high.  It is less sensitive to dirt than MIG but just as sensitive to wind.  It runs hotter than MIG typically would which makes it ideal for steel in the 3/8-1" thickness range.  Marine construction is almost exclusively done with dual shield.  7018 will be preferred for pipe welding as it is difficult to get the consistent penetration needed for pipe welding with any wire feed process.  Dual shield welds are typically welded from one side, back-gouged, then filled in from the other to give full penetration where pipe welding gives no access to the inside for back-gouging.Last edited by 76GMC1500; 11-27-2012 at 03:14 AM.
Reply:Thanks Jay & 76GMC1500,some great to the point explanations, much appreciated.You've just taught me a thing or two I never knew. The more you guys teach me the more I realise how little I know & have to learn.Keith.
Reply:I think these questions always want a simple answer and so much depends on the circumstances.  Given any process and a proper set of procedures the weld will perform to the required specifications.  It really is not important if one process is "better" than another.  Often between different contracting companies you will see different procedures and processes.  In the end they all meet the engineering requirements of the contract.   Note that Charpy impact values are listed at different temperatures.  Some welds are tough enough at room temp but in the freezing cold of a Northern Winter the weld would snap.  In the last ten years or so Charpy values have become important for earthquake zones as well as cold zones.