Hi Alfred,
I'm going to leave the answers to your problem for the ones on this forum that know more about your situation with working with welding the cast steel material.
However, I would like to know more about your inspection method that you are using to detect the cracks. I am not familiar with the designation of "FPI". Are you referring to Flourescent Partical Inspection (a form of MT)? Or is it Flourescent Penetrant Inspection (a form of PT)?
I'm guessing it's the latter of the two.
Just curious,
John Wright
Hi John,
Fluorescent penetrant is a variation of the dye penetrant method. It requires ultraviolet light to reveal defects. If there are defects, they appear in sharp glowing contrast to the surrounding flaw free surface. The fluorescent penetrant is an oil base agent with suspended fluorescent particles capable of penetrating every surface defect. It is applied by dipping, spraying, or brushing the piece to be inspected. After it has entered any seams, cracks, and pinholes, the surface excess is washed away with a water spray. When it has dried, a dry powder of water suspension developer is applied to dreate a dry powder film on the surface. This draws the penetrant up from the defect. The inspection is done under a black light in a darkened booth.
Another older simple method for detecting surface cracks in castings is to swab the damaged area with a kerosene soaked rag to remove dust and grease. Allow the kerosene to penetrate any cracks, then wipe the area dry. Immediately chalk over the area with ordinary blackboard chalk. After a few minutes, even cracks not visible to the naked eye become evident by the kerosene in them bleeding back through the chalk.
Hi Scott,
I'm very aware of the penetrant (PT) and mag partical (MT) testing methods using flourescent dyes for the PT, and flourescent particals for the MT wet, just hadn't heard it called "FPI". Additionally, with the kerosine method, flour could also be used as a developer if chalk wasn't readily available. I haven't done a lot of Flourescent PT & MT except checking some automotive parts for some racing buddies, but was qualified Level II here at work in those methods of inspection. Very rarely do I see requirements in the specs for us to PT anything, but MT (dry probe) is used quite a bit verifying rat holes in Group IV and V materials (mainly large section columns) and then some specs just call for 10% MT of all fillet welds. Here latey, I have been Mt'ing all pieces to be hot dipped because of all the troubles we have had with a certain galvanizer. I was just verifying that the cracks are not there after fabrication and before galvanizing, but are there after a certain galvanizer dips them.
John Wright
Hi Alfred,
Nodular iron, sometimes referred to as ductile iron, is available in several different metallurgical conditions. One ferritic form provides high ductility, another ferritic form provides high strength. A pearlitic form provides high strength, and an austenitic form provides maximum corrosion resistence, high temperatures, and thermal shock. Ductile iron is readily welded when in the ferritic and pearlitic state. When maximum strength and ductility are desired, the part should be in the fully annealed condition. The main concern in welding, then, is to reduce the rates of heating and cooling to prevent cracking. The more complex and massive the assembly, the longer the time and higher the temperature required for heat treatment. It is desireable to preheat the part to 550-750 degrees F and to reduce cooling by external heating. To ensure good penetration, it is desireable to remove the cast iron skin. Nodular iron can be welded by most welding processes, but regardless of the process used, the preferred practice is to use electrodes specifically manufactured for nodular iron. These electrodes have a composition of approximately 60% nickel and 40% iron, with a carboniferous lime-spar flux or coating. Should you opt to use SMAW, the E310-15, E310-16, and E7018 electrodes have been sucessfully used. Amperage should be low to insure minimum dilution and minimum local heating. 3/32" diameter should be at around 60-70 amps, 1/8" diameter should be at around 90-100 amps, 5/32" diameter should be at around 120-130 amps, and 3/16" diameter should be at around 140-150 amps. Parts should be covered with an insulating material to produce slow cooling. For best results, post heat treatments to 850 degrees F for four hours, or 1000 degrees F for two hours.
This link may be helpful:
http://www.twi.co.uk/j32k/protected/band_3/jk25.html
Alfred,
I would recommend welding without preheating with max interpasstemp 75 degrees Celsius (=160F). After welding 2-3 cm, immediately start hammering the hot bead until deformation of the bead is visible. This is to prevent stress due to shrinking of the weldmetal.
You mentioned solution treatment 900 F? This is (too) low for solution; it's even a low temperature for stress relieving. Or did you mean degrees Celsius?
Cracks in welding areas: be specific : in weldmetal or in HAZ?
Regards,
Erwin
Böhler Thyssen Welding
Alfred,
MIG-welding with the mentioned ER NiFe-CI could be ok, but in case you should hammer, SMAW could also be applied. I would not use E 7018 or 310. Specially develloped stickelectrodes gives best results, like UTP 8 (E Ni-CI) or UTP 86FN (E NiFe-CI).
Erwin
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