Cracks -- where'm I going wrong?

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I'm getting pretty consistent crater cracks on this project I just started. I've run into crater cracks before on occasion with 6010, but I've usually been able to solve the problem.I'm welding lengths of 1 1/4" re-bar to lengths of I-beam that I've cut in half lengthwise. The web of the I-beam is 1/4" thick and 5" deep after cutting. The re-bar sits on the cut, so the cross section looks something like a railroad rail. I'm step welding it with a 1 1/2" long bead and then a 1 1/2" long skip, then repeated down the 10' length. I'm using 1/8" 6010 and a beat up Miller Blue Star portable gas powered welder. On about 75% of the beads, I'm getting a good size crater at the finish. On most of these there is a small crack that starts at the very end of the bead in the center, runs parallel to the length of the bead through the crater and stops just after the crater. They're very short and grind out easily, but it's time consuming. The re-bar has ridges that are about 1/8" tall, so there is a 1/8" gap for most of the welds. Where the bead ends on a ridge, I don't leave a crater. It's about 70 degrees and windy, so I tried pre-heating, but that didn't seem to help. I've tried finishing the bead several different ways: pausing at the end for a second, then pulling the rod out quick, pausing then pulling the rod out slow, pausing for several seconds, and finally reversing direction and welding back over the bead for about 1/4". Nothing seemed to help except reversing direction, but even that wasn't 100%. I finally ended up changing over to 7018, but I'm still not happy with the fact that I couldn't get the 6010 to go. I weld alot with 6010 and don't tend to run into problems that I can't troubleshoot quickly.Anyone have any suggestions? Is there something basic that I've forgotten, or have I developed some bad habit over the years that hasn't bitten me until now?Thanks in advance.
Reply:it would really be nice to see a pic of the problem......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:My guess, without seeing some kind of a picture, would be due to cooling. What you have described... and my opinion is based on your description... sounds like Crater Cracks or Throat CracksCrater CracksDefinition: A crack, generally in the shape of an “X” which is found in a crater. Crater cracks are hot cracks.Cause: The center of the weld pool becomes solid before the outside of the weld pool, pulling the center apart during coolingPrevention: Fill the crater at weld termination and/or preheat to even out the cooling of the puddleYou said the preheat helped a little, but not all the time.... how hot was your preheat? Pictures would be a real plus.You also state that the 7018 worked ok..... so maybe it's an issue with the content of the rebar and 6010 rod.... so maybe it is more of a Throat Crack,Definition: A longitudinal crack located in the weld throat area.Cause: Transverse Stresses, probably from shrinkage. Indicates inadequate filler metal selection or welding procedure. May be due to crater crack propagation.Prevention: Correct initial cause. Increasing preheat may prevent it. be sure not to leave a crater. Use a more ductile filler material.Last edited by lorenzo; 12-27-2006 at 08:12 PM._________________Chris
Reply:Thanks guys. I'll see if I can get a good picture of the problem tomorrow. It looks like I used the wrong terminology though. They are almost all single cracks -- not x's. There were one or two that were perpendicular to the length of the bead, maybe these were crater cracks.I'm not sure what temperature I was heating to. I wasn't really set up to do an involved job of pre-heating. I'm working off a small trailer with an oxy/acetylene torch and a gas powered welder. I'll get some tempil-sticks in the morning and experiment a little. As far as not leaving craters, what is a good technique to finish a 6010 bead so you don't leave one. Are there some joint set-ups that will make it near impossible to do (too much gap)? Maybe rod size? I'll try to get some 5/32" 6010 and try that. Is re-bar typically made of something other than mild steel?
Reply:when i come to the end of a bead stick welding i go around in a circle..about the size of a big matchead a couple of times and then go up slow untill the arc stops..thats just me..but no crater either... ...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:Originally Posted by me37Is re-bar typically made of something other than mild steel?
Reply:No it can be of other grades and requires preheat and either 9018 or 11018 electrodes. Heres a link supporting the different grades.http://www.anvilfire.com/FAQs/reb_faq_index.htmhttp://www.mesteel.com/cgi-bin/w3-ms...ebar_sizes.htmLast edited by Dipper Welder64; 12-27-2006 at 11:39 PM.
Reply:I'm sure you like the 6010/6011 because of the cleaning action. The mill scale on some rebar can be a pain too. But that 1 1/4" rebar is pushing the limits without some preheat using 1/8th rod. The heat sink of the big rebar, the fast freeze and low fill rate of the 6010 all add up to those little cracks.  You'll be better off with something with a little higher fill rate and/OR more heat into it.
Reply:I'll ditto sandy, the metal is too thick to be welding without preheat, bring your metal up to 400 degrees and then weld, see if there is a difference. Good luck!If you don't have the time to do it right, then you definitely don't have the time to do it over.
Reply:CRATER FILL AT THE END OF YOUR BEAD (STOP TRAVEL AND FILLING THE CRATER TILL IT'S THE SAME LEVEL AS THE BEAD, MAY HELP TO REVERSE TRAVEL DIRECTION APROX. 1/8" AFTER CRATER FILL BEFORE BREAKING ARC.If its mild steel (A36) and soft grade rebar you should not need pre-heat unless it's over 1" thick and temps are over 50 degrees (F).SBG Welding
Reply:Hey guys, I got some pictures of the problem, but I can't get them to post here.Anyway.Picked up some 5/32" 6011 (shop didn't have 6010) and tried that. With no pre-heat it behaved just like the 1/8". With a lot of pre-heat it didn't crack. I don't know what temperature I'm working with because the local welding supply doesn't carry tempil sticks. Apparently they aren't used much in welding anymore (thats what the guy said).Anyhow, it looks like from what some of the folks here are saying, and what I saw this morning, it's an issue of pre-heat, and maybe even the filler rod. I was hoping to go with 6010 to cut down on prep time. The welds are not all that critical, and the faster I can get this done the better for everyone here. The amount of pre-heat needed to get the 6010 to go takes quite a bit longer than wire-wheeling the rebar to get the scale off and heating it up just enough to eliminate any moisture and sticking it with 7018. I'm actually duplicating something that's already been in service for quite a few years. I took a much closer look at that this morning. The welds all appear to be 6010/6011 and probably 80% have small cracks at the finish.Thanks for the help everyone.