Is it possible to weld SS with cast steel without any weld defects? If possible, which welding process will be preferable?
I think arc welding will be the preferred one and weld without any defects with SS, i don't know.
Cast Iron is difficult to weld. But in marine applications repairs to cracked components are not uncommon. In such cases cracked parts are prepared, heavily clamped and base metal is sufficiently (practical experience) heated and then welding is effected. Electric Arc Welding procedures can be followed to achieve good weld deposits. Further it is also common to drill holes in the cast irons, tap suitable threads and fix studs over the region to be repaired and welding is carried out after preheating to completely fuse studs into weld. Arc welding is carried out to completely to fill the studs with weld deposits. Bonding between the weld deposits and the studs prevents weld cracks. Further it is required to prepare the surface to avoid stress concentrations due to abrupt metal deposition in this cracked zone.
This shows how difficult it is to weld just the cast irons. !
Coming to welding of dissimilar steels like the stainless steel and cast irons, do not attempt to weld such things this is not logical engineering. Cast irons and stainless steels have different mechanical and chemical properties. Stresses would love to concentrate in this zone (if somehow they are fused !).
Nickel welding electrodes have a better tendency to prevent carbon absorption from the base metal for cast iron welding and hence they are used for cetain cast iron types. However, they are susceptible to cracking due to pick up of sulphur / phosphorus. So only just precise current is used (high currents are avoidable) to minimize this effect while welding. Some times low carbon type electrodes can be used but require much higher preheating for cast irons.
Suggestions:
1. Try to avoid welding cast irons to stainless steels. They are bad joints. Stresses as well as corrosion rates will be very high even if you use SUS 304 or 316L.
2. This one I am not sure (because I never attempted ) Try inserting some other steel like a carbon steel. Try bonding cast to this steel and then attempt stainless to this carbon steel insert (Doesn't sound like a good engineering practice but try if you cannot resist.)
3. Use bolting methods to join, use epoxy or such hard coatings to achieve tightness. (Looks like best one - as usually heavy engines are fixed on cast iron frames using this method.)
Professor Sadato HIRATSUKA of Iwate University in Japan seems to have carried out much research on the subject of welding stainless steel to cast iron (spheroidal). You could try to contact him ( [email protected]) and get some data or other advice from him on this particular subject.
I think that SMAW process using Ni electrode can be a suitable for joining cast iron to stainless steel. I suggest using "Cold Welding" technique. In this method, no preheating/PWHT is required and welding with low heat input must be applied.
I think it is quite difficult to join the two with arc welding process, since both materials have different properties but they can be joined by applying a buttering layer between the two. The buttering material properties should lie between the SS and cast iron.
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