trailing crack in weld?

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Hey Guys,      I have seen this in the past and thought it was due to using the wrong filler. But...I have a 16"long, 3"wide, 3/8" thick piece of hot roll carbon flat bar...Drilled a 1"1/4" thru hole, inserted a 16"x1"1/4" stainless round stock, 303 or 304....Tig welded on both sides of flat bar. I used 309L filler rod,(the rite rod for the job, I thought). In both top weld and bottom weld, more pronounced in bottom with it being a flat weld, a crack down the middle of weld followed the puddle. Can any one explain the reason for this. Any feed back is greatly appreciated..    Thanks, WesMiller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:Just paged thru the bible, and when using 309 to join mild to stainless the mild is supposed to be buttered with 309 prior to the actual final weld.Other than that, I'd hazard a guess that one of the metals is cooling faster than the other, and a preheat might eliminate the problem.  And that's only a guess.  Cracks usually mean the weld is cooling too fast."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammJust paged thru the bible, and when using 309 to join mild to stainless the mild is supposed to be buttered with 309 prior to the actual final weld.Other than that, I'd hazard a guess that one of the metals is cooling faster than the other, and a preheat might eliminate the problem.  And that's only a guess.  Cracks usually mean the weld is cooling too fast.
Reply:I would think that if 309 is a good filler for the stainless, that it can be used after the innitial buttering.  All my reference says is to butter mild with 309, then weld with the filler that matches the stainless.I wish I could help more, I only work with mild and some cast material."Any day above ground is a good day"http://www.farmersamm.com/
Reply:BTW, the only reference that comes from the bible is in the SMAW section.  No reference or discussion is included in the GTAW section that I could find.Are you sure TIG is the right process for what you're doing?  I'm not familiar with TIG, and I wonder if it has the capability to produce the heat necessary for larger pieces. Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Wes,The hot cracking you're seeing is a function of the metal chemistry and the cooling rate.You left out some details on the process, but I'll hazard a guess that you're not using any pre-heating on this weld. The weld sections, especially the shaft are pretty thick.  Some pre-heating is appropriate.The rapid cooling combined with the alloy content of the weld joint is producing a brittle structure called martensite in the weld.  This comes about from the dilution of the stainless steel in the bar with the mild steel in the flat strip.  Your 309 filler metal has a chemistry added to it that is designed to counter act this effect and reduce the chances of martensite forming.I've got a couple of suggestions that should help.  Some may or may not apply; as I don't know what procedure you're following.1 - Preheat the joint to 250 - 350 °F.  This will slow the cooling rate and less the chances of forming martensite.  2 - Make certain that the weld bead has a slightly convex profile.  A concave weld bead may look nice, and with fillets reduces the chances of a toe line crack, but a concave bead also increases the chances of centerline cracking.3 - If these suggestions don't work, you can try some changes to the filler metal you're using.  First, and least radical would be to switch to a 309L grade of filler.  The L is for low carbon, and carbon, amongst other things, promotes the formation of martensite.  If you reduce the carbon in the filler metal, you should lower the tendency to form martensite and therefore see this cracking.  The other thing to try, if this doesn't work/isn't practical, is to switch to  a filler with a higher nickel content.  THis will promote the formation of a different phase, called austenite.  Your 309 filler is supposed to do this, and has a fairly high nickel content to begin with.  But maybe your heat input or lack of pre-heating is producing a cooling rate that overcomes the ability of your 309 filler metal to compensate.As a last ditch effort, you might experiment with using something like 330 stainless filler. 330 has 2-3x more nickel in the alloy.  The cost may be prohibitive.  The risks associated with this are your responsibility to investigate.  You don't mention the end use for this part, so I can't speculate on what a change in filler metal might do.  Switching to 330 filler might require a different sized weld or may have other, un-intended, consquences. Originally Posted by waginHey Guys,      I have seen this in the past and thought it was due to using the wrong filler. But...I have a 16"long, 3"wide, 3/8" thick piece of hot roll carbon flat bar...Drilled a 1"1/4" thru hole, inserted a 16"x1"1/4" stainless round stock, 303 or 304....Tig welded on both sides of flat bar. I used 309L filler rod,(the rite rod for the job, I thought). In both top weld and bottom weld, more pronounced in bottom with it being a flat weld, a crack down the middle of weld followed the puddle. Can any one explain the reason for this. Any feed back is greatly appreciated..    Thanks, Wes
Reply:Samm,It is practical to TIG weld this joint.  It might take a bit more heat, but even a TIG power supply like a MAXSTAR 150 should be able to produce enough heat to achieve proper fusion.  A Dynasty 200 or 350 is easily up to the challenge, as would a TA185 or the equivalent Lincoln TIG machine... Originally Posted by farmersammBTW, the only reference that comes from the bible is in the SMAW section.  No reference or discussion is included in the GTAW section that I could find.Are you sure TIG is the right process for what you're doing?  I'm not familiar with TIG, and I wonder if it has the capability to produce the heat necessary for larger pieces.
Reply:Had same problem, cooling rate issue. Buttering will give plate preheat and help. Preheat both parts will solved issue for me.Peter
Reply:Originally Posted by A_DAB_will_doSamm,It is practical to TIG weld this joint.  It might take a bit more heat, but even a TIG power supply like a MAXSTAR 150 should be able to produce enough heat to achieve proper fusion.  A Dynasty 200 or 350 is easily up to the challenge, as would a TA185 or the equivalent Lincoln TIG machine...
Reply:IMO Cooling is the big issue here. I would be heating he solid 1" material 300-400 F or just before the straw color appears. I would make sure the HOT ROLLED is clean of all mill scale, in the weld zone + 3/4".I would be using 309L. I would make sure the weld profile was convex. I would bet $50.00 this solves all the cold cracking issues.
Reply:Mixing of steel and stainless steel will produce martensite which is brittle and will crack easily.  If you are TIG welding, you should try and minimize the dilution of the weld from the steel and maximize the content of stainless steel and the filler.  Another option worth trying is to use 321 as the filler which is higher in Cr as compared to 309 and will reduce the likelihood of martensite formation.Girish Kelkar, Ph.D.Independent Welding Consultanthttp://www.welding-consultant.com
Reply:My thanks to all for the reply s and great info/advice.....The piece I'm welding is to be a bed mount tool post/capture for a wood lathe........The filler I used is 309L, I purchased it to do a past similar job..... on ya'll's advice, I think preheat will solve the crack problem. I've encountered and dealt with the cracking issue in the past, but this is the worst I've seen. I'll do the pre- heat method tomorrow.                                                         Again, Thanks GuysMiller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:Hello wagin, I believe everyone has pretty well covered just about everything regarding why you had the cracking issues. I might only a couple of additional bits of information here. GTAW or TIG, whichever way you like to describe the process, has one of the highest dilution rates of just about any of the readily available welding processes. Aside from pre-heating and considering bead profiles( slightly convex to flat bead profiles being preferred over a concave profile), you can experience excessive mixing(dilution) of the 2 dissimilar materials that can promote cracking even when using "proper" fillers. That's where the buttering part can come into play, by applying materials on both sides of the joint that are more compatable, a weld can be placed that will be limited in it's cracking proneness. In some cases it's better to switch to processes that display limited dilution so that cracking can be minimized. I am not saying that is the case here, yet I believe this might make future challenges for you more explainable and give you other options to deal with them. One other condition to consider here, depth-to-width ratio, since GTAW/TIG has a fairly high depth-to-width ratio built into it's characteristics you might consider the grind angle of your tungsten as an additional point to pay attention to. Using a fairly long taper for your tungsten grind will aid in widening and limiting the penetration in the puddle and help to further limit centerline cracking. A bit more for you to consider. Best regards, Allanaevald
Reply:thanks aevald,   I try to learn something new from every job/project I encounter....(not very hard to do for me)HA. The information you shared was great. I did not know that the grind angle of tungsten tip had an appreciable influence on the width and depth of weld. See I learned something   Now to really sound dumb, referring to the term/process of buttering. What is the procedure??Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:never mind about the buttering question....DuHu.. FarmerSamm posted apic of the bible detailing the process.Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:I will hazard the guess that your problem may not been correctly diagnosed.  A_DAB_will_do mentioned "hot cracking", but then he and others went on to describe the problem of "cold cracking" associated with dissimilar SS + CS welds, where the weld chemistry results in a brittle structure.  This can definitely be a problem, but if the 309 filler is not over diluted, it should be ok.The hard brittle dissimilar weld would probably tend to crack along the HAZ/weld toe line on the CS side of the joint, not typically down the weld center line.  The brittle weld is also much stronger than the SS or CS base metal HAZ, so typically as the weld contracts, the SS side is ductile and will stretch, while the CS HAZ is not so ductile and it fractures.You very likely have hot cracking, and if your bar is 303 like you mentioned, you definitely do! 303 SS is a "free machining" grade with a lot of extra sulfur added to provide a structure of manganese sulfide stringers in the material which makes it easier to cut.  Sulfur in the weld melts at a much lower temperature than the steel, and it gets pushed to weld center as the weld solidifies from the perimeter toward the center.  As the weld has just solidified, the sulfur around the grain boundaries in the weld center is still liquid, and the tensile stresses of weld shrinkage open up the hot crack.Center line cracking is a classic indicator of hot cracking, and a circular weld, like around your bar, is the worst joint configuration since it produces the highest weld contraction stresses and so it is classically related to hot cracking,  There is even a hot cracking test used to evaluated materials, which is a "circular patch test", or "Houldcroft test".Even 304 SS bar could give you problems with hot cracking because of the highly restrained circular weld joint.312 SS filler can help prevent hot cracking better than 309 because it forms more ferrite which ties up more sulfur in solution so that less sulfur goes to the grain boundaries.
Reply:wagin, hello, are you there?What happened with your HOT CRACK, or was it a cold crack?Was it 303 SS bar, or 304?   There is a huge difference.
Reply:Originally Posted by pulserI will hazard the guess that your problem may not been correctly diagnosed.  A_DAB_will_do mentioned "hot cracking", but then he and others went on to describe the problem of "cold cracking" associated with dissimilar SS + CS welds, where the weld chemistry results in a brittle structure.  This can definitely be a problem, but if the 309 filler is not over diluted, it should be ok.The hard brittle dissimilar weld would probably tend to crack along the HAZ/weld toe line on the CS side of the joint, not typically down the weld center line.  The brittle weld is also much stronger than the SS or CS base metal HAZ, so typically as the weld contracts, the SS side is ductile and will stretch, while the CS HAZ is not so ductile and it fractures.You very likely have hot cracking, and if your bar is 303 like you mentioned, you definitely do! 303 SS is a "free machining" grade with a lot of extra sulfur added to provide a structure of manganese sulfide stringers in the material which makes it easier to cut.  Sulfur in the weld melts at a much lower temperature than the steel, and it gets pushed to weld center as the weld solidifies from the perimeter toward the center.  As the weld has just solidified, the sulfur around the grain boundaries in the weld center is still liquid, and the tensile stresses of weld shrinkage open up the hot crack.Center line cracking is a classic indicator of hot cracking, and a circular weld, like around your bar, is the worst joint configuration since it produces the highest weld contraction stresses and so it is classically related to hot cracking,  There is even a hot cracking test used to evaluated materials, which is a "circular patch test", or "Houldcroft test".Even 304 SS bar could give you problems with hot cracking because of the highly restrained circular weld joint.312 SS filler can help prevent hot cracking better than 309 because it forms more ferrite which ties up more sulfur in solution so that less sulfur goes to the grain boundaries.
Reply:Pulser,Thanks for the correction.  I apparently lost my train of thought and didn't clearly understand the original post when I replied.  After re-reading the original post, I agree with your assessment.  I was wrong; it's what I get for answering technical questions on too little sleep. Originally Posted by pulserI will hazard the guess that your problem may not been correctly diagnosed.  A_DAB_will_do mentioned "hot cracking", but then he and others went on to describe the problem of "cold cracking" associated with dissimilar SS + CS welds, where the weld chemistry results in a brittle structure.  This can definitely be a problem, but if the 309 filler is not over diluted, it should be ok.The hard brittle dissimilar weld would probably tend to crack along the HAZ/weld toe line on the CS side of the joint, not typically down the weld center line.  The brittle weld is also much stronger than the SS or CS base metal HAZ, so typically as the weld contracts, the SS side is ductile and will stretch, while the CS HAZ is not so ductile and it fractures.You very likely have hot cracking, and if your bar is 303 like you mentioned, you definitely do! 303 SS is a "free machining" grade with a lot of extra sulfur added to provide a structure of manganese sulfide stringers in the material which makes it easier to cut.  Sulfur in the weld melts at a much lower temperature than the steel, and it gets pushed to weld center as the weld solidifies from the perimeter toward the center.  As the weld has just solidified, the sulfur around the grain boundaries in the weld center is still liquid, and the tensile stresses of weld shrinkage open up the hot crack.Center line cracking is a classic indicator of hot cracking, and a circular weld, like around your bar, is the worst joint configuration since it produces the highest weld contraction stresses and so it is classically related to hot cracking,  There is even a hot cracking test used to evaluated materials, which is a "circular patch test", or "Houldcroft test".Even 304 SS bar could give you problems with hot cracking because of the highly restrained circular weld joint.312 SS filler can help prevent hot cracking better than 309 because it forms more ferrite which ties up more sulfur in solution so that less sulfur goes to the grain boundaries.
Reply:Originally Posted by pulserwagin, hello, are you there?What happened with your HOT CRACK, or was it a cold crack?Was it 303 SS bar, or 304?   There is a huge difference.