Fusion Welding

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I dont know if that's what it's called, but when fusing two bits of metal without filler wire...same strength as parent material?  Any issues with this procedure?  Prone to failures?  When would this be better/worse than using wire?Search function = no go.ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:Stainless and Titanium can be fused together easily..So can Cast Iron and Aluminum with the right R.P.M. and oil pump failure..  ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Many materials can be fused without filler. In addition to the stainless and titanium, pure copper, some aluminum alloys, low carbon steel, some copper alloys (brasses and bronzes), and a few others.Virtually all low carbon can be fused without a problem. A few alloys give problems with cracking, in particular those meant for easy machining. Common hot roll (A36, etc) and cold rolled alloys are fine.Any stainlesses that can be welded using a matching filler can be fused to the same or similar alloys. Stainlesses that need non-matching filler (reduced carbon, modified alloy chemistry, etc) to avoid cracking, carbide precipitation, and other ills, shouldn't be fused. For example, most of the 300-series alloys can be fused successfully with the proper procedure.Most aluminums NEED a non-matching filler to control the chemistry in the weld zone, or cracking will occur, and shouldn't be welded without filler.Etc......Basicly, if the filler is the same chemistry as the base metal, and there arn't special additives in the fillers (like extra deoxidizers, trace elements to refine the melt, etc), fusing is fine, and the weld will have the same properties as if welded with filler.Cleanlinedd is MORE important than when using filler, as most fillers will have a small amount of additive to deal with trace impurities in the weld. Clean is critical for TIG. Cleaner yet is needed for fusing.
Reply:Thats cool!..Learn something new every day...Good explination in easy to read text.. Nice to have a metalurgest (sp?) here..Im no metalurgest?  ..I just know how to weld.. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Not a metallurgist (sp?). Just an (oh no, here comes the admission of guilt) engineer. (ducks to avoid the pitchforks. I don't mind the torches, but the pitchforks sting  )I do a bit of many things: hold current papers (ASME shop) for GTAW and SMAW all positions (1G through 4G, didn't bother with small pipe 6G as we have other people that can do it better), am the engineer for pressure vessel repair, assist our level-3 on NDE (learning a lot, don't know much yet), do job planning (despite the best efforts of the powers that be to thwart any plan), do diesel and heavy equip maintainance when needed, electrical work when needed, am a satisfactory machine operator when pressed (not machinist, but I have cut 48TPI on 0.040 wall tubing), and am still skinny enough, barely, to go through a small manway to drive pins and buck rivets. Been getting away from some of this as other people sign on that are more qualified to do some of this... I'v even had a few weekends off in the last six months!  Oh, and I teach engineering (been doing that for 15 years).Last edited by enlpck; 03-24-2007 at 08:53 PM.
Reply:So, if my "fitting" tolerances are tight enough, and the material is clean enough, I should have no qualms about fusing while I build my table?  For once Im happy to hear from an engineer!ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:You could fuse it, though I wouldn't. Typical applications for fusing are thinner pipe, like stainless process pipe in a brewery, sheet metal joints, etc. Usually butt welds or lap welds (where you can melt the corner down). They are a special purpose  type weld.I would have no qualms about tacking without filler, but unless you want to spend some time doing practice welds and cutting them apart to be sure you are getting sufficient penetration, and want to do the welds from both sides, I would use filler for the final welds. It is tougher to get a good weld fusing.Experiment, and you'll see  a) how easy it can be, and b) how tough it can be to get consistant, quality welds this way.
Reply:Ok, here we go, settle in for a long read... most of this will concern welding steels as I don't have a whole lot of metallurgy training in non-ferrous metals.The two biggest concerns with welding without filler are hardness (due to cooling rates, a.k.a quench rates) and weld profile.Carbon ContentGenerally, the higher the carbon content the easier it is to harden a steel. For example, (real) wrought iron, has very little carbon in it (even less than your mild and low carbon steels) and is therefore very soft, whereas tools steels usually have high carbon contents and are therefore very hard. Cast iron usually has even higher carbon content and can be very hard.Usually, the harder a steel is, the more brittle it is, which is usually a bad thing where welds are concerned.Cooling Rates and Grain StructureNow, carbon content isn't the only thing that makes a steel hard, the speed at which it is cooled from a molten or near molten state to around ambient temperature also plays a big part.Steel is an interesting alloy because it is one of the few that can have several grain structures (forms of the crystalline matrix). The most commonly encountered are austenitic, pearlitic, ferritic, bainitic, and martensitic. Austenite - When your average mild steel just begins to solidify, it has a austenitic grain structure. One of the interesting things about this structure is that it is the only one that is non-magnetic.Ferrite - This is one of the possible grain after the steel cools down below around 1333 degrees F (this number varies by alloy). It is relatively soft and ductile.Pearlite - Another possible grain structure when cooling from austenitic. Still fairly soft, but not as soft as ferrite.Bainite - Yet another possible grain structure when cooling from austenitic. Harder than ferrite and pearlite.Martensite - Still another possible grain structure when cooling from austenitic. This is the hardest and most brittle grain structure of them all. Martensite in or around a weld is usually very undesirable.If you heat a steel above the upper transformation point (the point at which the grain structure becomes austenitic, ~1333 degrees F for mild steel) and then allow it to cool very slowly the structure will end up being almost entirely ferritic and the steel will be soft and ductile. If you cool it slightly faster you will end up with a mix of ferrite and pearlite, and the steel will slightly harder and less ductile. Cool it even faster and you get less ferrite and pearlite, and more bainite along with an increase in hardness and drop in ductility. Cooling faster ans faster will result in more and more bainite. Finally if you cool it really fast, you end up with martenisite.The exact rates of cooling required to get each grain structure varies by alloy. Generally, the lower the carbon content the faster you can cool it without having to worry about getting the harder grain structures, whereas the higher the the carbon content the slower you have to cool it to prevent hardness. For example, low carbon steels can be welded and then dunked in a bucket of water with relatively little hardening (it's still not good practice so don't do it) whereas if you weld on higher carbon steels and some cast irons and let them just air-cool after welding they will become very hard, brittle, and possibly crack.In welding, the rates of cooling involved are pretty fast. If you start on a cold ("cold" meaning ambient) work piece and run a bead, pretty much any point on the weld will go from molten (3000+ degrees F) to only a few hundred degrees in just a few seconds. On mild steels, even this cooling rate results in only minor hardening. However higher carbon steels tend to have to be preheated and then post-weld heat treated to slow the cooling rates to prevent excessive hardness and cracks.However, generally, in welding the heat of welding is so concentrated that even though the puddle itself is molten the steel less than an inch away might not even get up above the transformation temperature. But it is the steel that is close enough to the puddle that it is taken up into the austenitic range and then rapidly cooled that encounters the change in structure that is of the biggest concern to welders. This area is called the heat-affected zone (HAZ) and the most common source for problems.The reason that the HAZ is a bigger source of problems resulting from cooling rates than the weld itself (despite the greater cooling rates of the weld metal) is that, the majority of filler metals used contain considerably less carbon than the base metal, and therefore don't harden as easily or severely.Other Alloying Elements and Stainless SteelsNow, carbon isn't the only alloying element that affects the transformation temperatures (and therefore hardenability), it is however the most potent.Stainless Steel comes in three main types: austenitic, ferritic, and martensitic. The austenitic stainless steels make up the 300 series. Because of the high level of nickel the upper transformation temperature is actually well below room temperature. This means that no matter how fast you cool it, all you'll end up with is an austenitic grain structure, hence austenitic stainlesses are called non-hardenable. The austenitic structure is also why 300 series SS is non-magnetic. The high nickel content is why these steels are so expensive.The ferritic and martensitic stainlesses make up the 400 series. Neither have very much, if any, nickel content, just lots of chromium to provide corrosion resistance. Both are magnetic since they do transform out of the austenitic range. Ferritic has enough carbon to be hardenable, but not a whole lot, it's cheaper than austenitic and is used a lot in cheap silverware and pots and pans. Martensitic has a higher carbon content and is easier to get to transform into martensite. One of the only real reasons you would want martensite is because, due to it's hardness, it can hold an edge really well, hence blades for pocket knives, scalpels, razors, and just about everything else that needs a good sharp edge is made out martensitic stainless steel.The journey to Get Back On TopicOk, now that I've given a little bit of background information as far as metallurgy goes, let's apply it to welding without filler.As enlpck, said most low carbon/ mild steels can be welded without filler since they don't harden much. The reason you have to look out for the free-machining steels is because these have a higher level of sulphur (when machining, sulfur makes the chips break up instead of forming long and sharp strands) than regular steels. When welded, free machining steels have a tendency to hot-crack due to the sulfur. Filler metals for these steels have elements in them that seek out the sulfur and keep it from causing hot-cracking.However, higher carbon and higher alloy steels should not be welded without filler since it will be the base metal instead of the filler metal that experiences the higher cooling rates thus making them more prone to brittleness and cracking. For example, 4130 is a fairly common steel containing chromium and molybdenum that is used a lot for roll cages, race car frames, and some aircraft frames. If it is welded without filler it has a strong tendency to produce martensite and crack.Austenitic (300 series) stainless steels are pretty safe to weld without filler since, like I said before, it won't really harden no matter how fast it cools. As enlpck said, there are some exceptions, however, carbide precipitation is an issues with 300 stainlesses whether filler is used or not.Fully Back on TopicNow, that's the metallurgical side (or some of it anyway) of welding without filler. As far as technique and such... well... why would you want to?The reason it is used on thinner pipe and such is because those welds are often very special, using perfect fit-up (when I say "perfect," I mean it, they have zero gaps), automation equipment, are carefully designed to be full-penetration, and do not end up being any lower than the outside surface of the pipe/tube.It is also common on sheet metal because it is faster and requires very little actual skill to end up with a "pretty" weld.I agree with enlpck in that I have no problems doing it just for tacking. However, I see no reason to do it for an entire weld (even if it's just a root pass) because any idiot with half of a brain and one arm can do it, and you'll never be a good welder if you always take the easy way out and never challenge yourself.For example, in this thread ( http://www.weldingweb.com/vbb/showthread.php?t=10187 ), for some reason, Zap did the first pass (root) without filler. I really have no idea why he did this. You can't argue that it's for penetration purposes because a truly skilled welder using GTAW (TIG) welding should be able to get the same amount of penetration even when adding filler. If he had just added filler, he would've ended up with the same strength and size weld, but would've only had to go around that thing three times instead of four (saved time and therefore money). Also, the higher travel speed that is often inherent in welding without filler results in faster cooling rates, and thus brittleness and possible cracks that might not be removed by later passes. Then again, maybe I should go post this in that thread...In summary, 99.9% of the time, you should use filler, it's better not only for your welds but for your developing skills as well.A Parting ShotOne last thing before I (finally) end this post...You may have noticed that I did not use the word "fusing" or phrases "fuse welding" or "fusion welding." There is a very good reason for this."Fusing" and "fusion welding" does not mean what everyone here seems to think it means."Fusing" and "fusion welding" simply means that at least some of the base metal is melted and becomes part of the weld. It is equally applicable whether filler is being used or not. (Brazing and soldering are not considered fusion processes because the base metal is not melted.)The proper term for welding without filler is "autogenous welding."-- Tensaiteki-- AAS Welding Technology TSTC August 2007Visit Tensaiteki.com
Reply:I think weve just been educated.  I understand that chemical composition and carbon content have everything to do with the temper of the metal in the weld zone (HAZ as you put it).  But lets say for mild steel, am I right in the fact that the weld (with filler used) will be harder than the surrounding steel, thus more brittle?  I was told this by another fella, and it made sense to me.  But in some cases such as stainless, the area around the weld or HAZ area could become brittle and crack instead of the weld?I never liked the idea of not using filler as I allways thought the filler mixed with the base material to help keep the properties of the original material.  Does back gassing stainless help prevent these effects you have described?  Thanks.Various GrindersVictor Journeyman torch200cf Acet. 250cf oxygenLincoln 175 plus/alpha2 gunLincoln v205t tigLincoln 350mpEsab 650 plasmaWhen you can get up in the morning, Its a good day.Live each day like its your last.
Reply:Originally Posted by enlpckNot a metallurgist (sp?). Just an (oh no, here comes the admission of guilt) engineer. (ducks to avoid the pitchforks. I don't mind the torches, but the pitchforks sting  )I do a bit of many things: hold current papers (ASME shop) for GTAW and SMAW all positions (1G through 4G, didn't bother with small pipe 6G as we have other people that can do it better), am the engineer for pressure vessel repair, assist our level-3 on NDE (learning a lot, don't know much yet), do job planning (despite the best efforts of the powers that be to thwart any plan), do diesel and heavy equip maintainance when needed, electrical work when needed, am a satisfactory machine operator when pressed (not machinist, but I have cut 48TPI on 0.040 wall tubing), and am still skinny enough, barely, to go through a small manway to drive pins and buck rivets. Been getting away from some of this as other people sign on that are more qualified to do some of this... I'v even had a few weekends off in the last six months!  Oh, and I teach engineering (been doing that for 15 years).
Reply:Geez Tensaiteki...thanks for the complete diagnosis!  That really helped me comprehend the concerns I had.  Im pretty new here, and was just guessing on the terminology.  Did some autogenous welding while fooling around (learning/experimenting) yesterday.  Never tried it before, and wondered just how many others do this technique.Thanks for the insightful write-up!ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:Whoops.... I should have caught the misuse of terminology. I'm so used to seeing and writing "fuse with no filler" in procedures, I didn't even think about it. Half the people I have  worked with would ask "who's Otto, and whys he so smart?" or tell me not to talk dirty is I said 'autogeneous'  tresi: not an impressive resume. You do what you need to do. I'd rather work than take vacation, and take what opportunities I can to build skill. I look at times when I'm not teaching as opportuities to do something different, and don't tend to take jobs that are just for the cash- I'd have more money if I did. I prefer to do something interesting and, if possible, a little different. Just because someone else can do something better doesn't mean I can't learn to do it well enough.
Reply:i dont think i saw it in the above posts, but the word your looking for is an intagnious weld.
Reply:So, is it intagnious or autogenous welding?ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:my bad, ive only heard it never seen it spelled, autogenous is prob the proper spelling.