How do I keep this weld from cracking?

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Trying to weld up a crack on the front face of a monolithic hydraulic valve body. The body is cast steel. I've got 2 cracks between spool bores on the face. The metal here is about 1/4" thick with a passage behind it. I v-ed out the cracks till there was about 1/8 left (didn't want to completely take it out as I can't get behind it to put a back up plate in) and proceeded to try welding it up. Started trying to use the TIG with about 200 amps and regular steel filler wire. (not sure what alloy - the generic copper clad welding rod). The weld went down nicely but cracked clean through within about 20 seconds. I had a propane torch on the weld area trying to do some preheating. After this I ground it back out and tried again with more preheat but with the same effect. I've tried MIG as well and even tried heating the surrounding area almost red hot with the torch pre/post welding and it still cracks. Any ideas how to do this? Seems pretty clear to me I've got thermal stress issue from contraction of the weld but I can't think of what to do about it short of trying to weld it in an oven. It actually seemed like the more I tried to preheat the quicker it would crack. This is after the final time I tried MIG welding - Ugly weld but at this point I was pretty sick of trying......
Reply:Originally Posted by sdmulemanTrying to weld up a crack on the front face of a monolithic hydraulic valve body. The body is cast steel. I've got 2 cracks between spool bores on the face. The metal here is about 1/4" thick with a passage behind it. I v-ed out the cracks till there was about 1/8 left (didn't want to completely take it out as I can't get behind it to put a back up plate in) and proceeded to try welding it up. Started trying to use the TIG with about 200 amps and regular steel filler wire. (not sure what alloy - the generic copper clad welding rod). The weld went down nicely but cracked clean through within about 20 seconds. I had a propane torch on the weld area trying to do some preheating. After this I ground it back out and tried again with more preheat but with the same effect. I've tried MIG as well and even tried heating the surrounding area almost red hot with the torch pre/post welding and it still cracks. Any ideas how to do this? Seems pretty clear to me I've got thermal stress issue from contraction of the weld but I can't think of what to do about it short of trying to weld it in an oven. It actually seemed like the more I tried to preheat the quicker it would crack. This is after the final time I tried MIG welding - Ugly weld but at this point I was pretty sick of trying......
Reply:v it out more try and heat the whole thing to 350 not just one spot slowy cool down . whats going on in the right pic look very dirty are you cleaning everthing well
Reply:Originally Posted by Bigrich954rrv it out more try and heat the whole thing to 350 not just one spot slowy cool down . whats going on in the right pic look very dirty are you cleaning everthing well
Reply:Not sure what temp it is, I'm trying to heat it with the torch - don't have anything fancy. Can't really v out much more without going completely through. I'm leaving about 1/8" of the base metal at the bottom of the v, should I leave less?Weld on the right is the 2nd crack - Put one bead down before I discovered that they were cracking and that one obviously had some sort of contamination - I think there was a drop of hydraulic fluid or something still there. Didn't bother grinding it out to fix until I figured out the cracking problem. The bead at the top right is part of a repair on a crack on the back - that was the first issue with this valve and was repaired in the tractor. Seemed to work well but I suspect thermal stress from that fix is what caused these cracks.
Reply:themal stress on an edge shouldn't affect the middle. the entire valve body is probably being stessed some how while in place. you can tinker with putting the graphite from carbon arc rods in the passage behind to back up the weld. I would contact member CASTWELD for advice.Dynasty 200DXPassport plus w/ spoolmate 100victor 315c oxy/(act and prop)Miller digital elitemilwaukee power tools
Reply:sdmulemanKnow what you are welding;know how to weld it; have it done by competent welder;because no one can unscramble an egg.Opus
Reply:At this point I would guess the cracks on the face are the least of your concerns. Cracks extending into the bores, as well as warping of those bores may be a bigger challenge.
Reply:I would have think that the crack extends well into the area between those two spool bores and that even if you successively weld the crack you will not have fixed the problem. Most c/valves are cast iron and the pictures seem of the weld deposit look to me that it is cast iron. I think you are wasting time with your efforts. Buy a new valve and be done with it
Reply:Stick it in the oven for an hour or so at 350-400, pull it out and weld it and stick it back in the oven at 300ish, then back the oven down 50 degrees every 20 minutes or so. Peening the weld helps as well.I had a head that was to big for my oven not long ago that I needed to weld up. I made half of an enclosure with scrap sheet metal and stuck the head in the enclosure, then I stuck a ready heater in front blowing hot air into the enclosure. With a laser gun I watched the temp in multiple spots on the head and moved the heater around slightly to keep an even heat on the head. After about 3 hours the head was at 400, I did the welding and then stuck the head back in front of the ready heater. I then just kept moving the ready heater farther and farther away from the head until I had it down to around 200 degrees. Worked like a charm.A year or so ago I used fire to heat a shear head I had to weld back together which also worked like a charm.http://weldingweb.com/vbb/showthread.php...st-welding-fun
Reply:The cracks I have do not extend into the bores - there's an oil passage between the front face area and the actual spool bores. The only thing they go through (so far) is the sealing area of the spool bores. If it was cast iron wouldn't it be cracking in the base metal and not the weld? I'm for sure leaning towards replacing the valve at this point although I have not yet been about to find one that's economical. Even if I do replace it I'd still like to know if/how this repair could be done for future reference.
Reply:When you guys say stick it in the oven at xxx degrees are you setting the oven to that temp or do you want the base metal to be that temp? How much do you worry about it cooling off between the oven and welding? Are you putting it back in after each pass or just welding it all then putting it back?Also, what kind of oven do ya'll use?
Reply:Have an old O/A welding handbook with a chapter about welding cast iron. One suggested method for preheating is to build a temporary coal burning fire pit (correct word?) out of fire brick, have holes on the bottom where you can regulate incoming air and cover most of the top with asbestos (hey, it's a 50 year old book!) or sheetmetal. Basically, you put the broken part in there, load it up with coal and start the fire (putting cold metal in a hot oven may heat it up so uneven it cracks), wait until the metal is red hot (they actually warn you about not letting it get so hot it melts) pull the sheetmetal/asbestos aside so you get a small opening just over the area to weld and weld it through there. When done welding, cover it up again, restrict the air inlets so it burns slower, and leave it to cool down slowly for 24h or something like that.Have you considered brazing it? Requires much lower temperatures than welding, which makes metal shrinking as its cooling down a smaller issue (no pun intended).
Reply:Looks like cast iron to me too. If casting is not over 1/4 inch thick everywhere I'd grind that mess out, heat to 650 in oven a with a good heat soak period and braze that thing up. If parts of the casting near weld area thicker than .4 inch, I'd heat to 950.  Post heat and a slow cool also. Brazing will make it easier on the machinist. Castings are nearly impossible to arc weld without leaks.Or you can OA spray weld it also. Oh.. High nickel rods are a must to be able to machine after welding.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:Originally Posted by castweldLooks like cast iron to me too. If casting is not over 1/4 inch thick everywhere I'd grind that mess out, heat to 650 in oven a with a good heat soak period and braze that thing up. If parts of the casting near weld area thicker than .4 inch, I'd heat to 950.  Post heat and a slow cool also. Brazing will make it easier on the machinist. Castings are nearly impossible to arc weld without leaks.Or you can OA spray weld it also. Oh.. High nickel rods are a must to be able to machine after welding.Peter
Reply:What I would do is similar to what the others have said...heat the whole piece, localized heating will add to your heat stress in the entire part, as far as welding it here is what i'd dowait till the wife goes to work, put the CLEANED part into the oven in the house (dishwasher works great for cleaning if you can get away with it) and pre heat the piece for a good soak at say 350-400 deg for maybe 2 hours (length of time depends on size of piece). when you pull the piece out lay in one pass with tig or stick and a high nickel electrode. replace into oven and let the HAZ cool to the same temp or close to the same temp as the rest of the parent metal -you could buy a temp stick to get a rough idea of temp-. repeat this process until the welds are flush/full. welding cast anything is a pain in the butt....it can be done but it takes time and patience. oh and post heat....ramp the heat down slow (think hour(s) before taking it out of the oven) once you are finished weldingI have heard of guys welding heavy pieces of cast by dropping a ceramic blanket over the piece and putting one or two tiger torches under it for pre heat until its almost red then just going in and pulling the blanket away every hour or so, lay a bead and put it back over...takes all day to weld a piece but they can have other jobs on the go while working on it.also doing your bevel almost the full thickness of the parent metal is not always the best idea....when repairing cast the bevel should not be more than 1/3 of the material thickness if i remember right...reason being that you want to minimize the amount of heat input and stress from welding...plus your weld is going to be much stronger than your parent metal anywaysgood luck, hope this helps
Reply:Originally Posted by sdmulemanI'm for sure leaning towards replacing the valve at this point although I have not yet been about to find one that's economical.
Reply:I recall reading something about cast iron needing to be post weld heat treated and cooled at a (relatively) snail's pace.Someone suggested peening. That would help.Then again, I also read that if you have to weld cast iron... don't. Best of luck. I'd like to see how it finally turns out.
Reply:Originally Posted by akabadnewsI recall reading something about cast iron needing to be post weld heat treated and cooled at a (relatively) snail's pace.
Reply:It is cast iron. Even if you successfully weld it your cracks o to deep to fix with a surface weld. You will not be able to machine the part back down after your weld unless you use a high nickle rod. Silver solder would have been a better repair.
Reply:Preheat in an oven, have a pile of mineral wool to wrap the part in during welding, then back in the oven after welding and let it cool down very slowly.
Reply:Well, after looking at it again I have to agree that it's cast iron. Not sure why I was so firmly convinced it was steel, but that does certainly explain the cracking problem. Makes me really somewhat astounded that it didn't crack from the booger welding I did on the back face earlier - there was no preheat at all doing that and I did a fair amount of welding and grinding trying to get it sealed up fully. All of the advice on welding is much appreciated. Now that I know it's iron there's no question in my mind why I had problems welding it. Would brazing be strong enough for a crack like that? Seems like it might if you could insure full penetration of the entire 1/4"+ depth of the crack, but without being able to get to the bottom how would you make sure it got that deep? The passage below this front face has up to 2000 psi oil in it, so there's a decent amount of force pulling that crack apart under load. Thanks,    ~John
Reply:Would brazing be strong enough for a crack like that? Seems like it might if you could insure full penetration of the entire 1/4"+ depth of the crack, but without being able to get to the bottom how would you make sure it got that deep? The passage below this front face has up to 2000 psi oil in it, so there's a decent amount of force pulling that crack apart under load.  V out wide enough and leave about 1/8 gap, that should give full pen. Check out the tensile rating on your brazing rod, the two I use are 60,000 and 80,000. Common cast iron castings are usually in the 40,0000 range.Equipment:2  old paws2  eyes (that don't look so good)1  bad back