American Welding Society Forum
I am Alfred from Indonesia,
I have problem with weld Nodular cast iron.( D-5B). we weld with GTAW and the filler is AWS A5.14 (ERNi-3).
the procedures are :
1. solution treatment
2. preheat to 200-250 deg. celcius
3 weld while hot
. cool in the air
5 stress release
6 Penetrant Inspection, we found crack on weld and HAZ
the purpose of welding, a.. Repair/ refurbish the part
the thickness a.. 5 to 7 mm
the length of welding, a.. 20 to 75 mm
preparation a.. Chenical cleaning ( degrease) and gouge by hand grinding ( metal carbide)
the parameters of solution treatment a.. 900 deg.F for 3 hr. furnace cooling
.preheat a.. by manual torch on weld area
measure the temperature a.. by pyrometer ( special thermometer)
What do you mean by "stress relief" ?
Is it by means of postweld heat treatment ?
It looks like your problem is the formation of brittle phases in the HAZ, resulting in less ductility of the base material.
Some guidelines :
First of all I would not recommend the GTAW proces : it is a high concentrated heat source, causing higher cooling rates for the base material. I prefer the MMA, with small diameter stick electrodes for this application. (try to weld with DCSP = stick electrode on negative pole to limit the dilution of the weld)
(1) prefer gouging electrodes instead of grinding ; with normal grinding, the impurities and graphite in the cast iron are smeared out along the groove and may cause problems ;
(2) try to use the buttering technique : this means that one or both of the surfaces to be welded are clad prior to welding. This technique is used to avoid the formation of brittle phases. The contarctional stresses from the cooling weld metal in subsequent beads can be absorbed more on the ductile buttering layer than the brittle HAZ of the base material
(3) reduce contractional stresses after welding each bead. Peen each weld bead surface with a rounded tool directly after welding : from the center of the weld towards the edges of the base material.
(4) weld with short stringer beads (20-33 mm long)
(5) allow very slow cooling : NOT in the air, but cover the workpiece with a thick heat resistant blanket ; remove the blanket if the temperature of the workpiece is below 60 deg. Celcius (if you remove the blanket at higher temperatures, you can introduce cracks directly when exposing the workpiece to the cold air = temperature shock) You can also consider to cover the piece in a pile of sand.
(5) limit the heat input : use the lowest possible current and the highest travel speed.
Good luck !
When welding any cast iron, you will end up with a brittle (martensitic) structure, even though the nodular iron is ductile. This is because of the high cooling rates experienced during welding. If you want to ensure that you have a ductile HAZ, then you need to have pre-heats of around 500 - 600°C. In addition, if you want a ductile weld metal, you will need to use a suitable filler.
You can therefore pre-heat the component to 600°C and weld with a cast iron welding consumable (typically Ni based) to get a ductile weld. If the high pre-heat is not feasible (which often it is not) then you will just have to accept that the HAZ will be brittle, and just go for trying to minimize the size of the HAZ by using NO pre-heat, and a Ni welding consumable to give a ductile weld that can "give" while welding. You need to minimize heat input when using this approach.
I can not find ERNi-3 in A5.14, so I am not sure if I am missing it, or if you have the wrong spec. At any rate, I do not think that these fillers are really made for welding cast irons. We always use SMAW electrodes because these have a flux specially made to help in welding cast irons.
I also do not know why you would want to solution treat the nodular iron. It should be delivered in the optimum condition. Your "solution treatment" temperature is also so low, that I do not believe that you can actually get "solution" occurring. If anything, this treatment may help to drive off contamination. (AS such, it may be valuable.) In addition, the stress relieve operation will not necessarily improve the properties, but as long as you do not exceeed the transformation temperature, you would probably not do too much harm.
What you need to keep in mind is that possibly you are picking up cold cracking, that could be occurring before you perform the stress relieve treatment. This problem should be minimized if you use high interpass temperatures and maintain these for a period long enough after welding, to ehsure that all Hydrogen has been driven off.
Hope this helps.
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