Cast stainless with low magnetic permeability

[gieter]

Dear all,

I'm looking for a castable stainless steel or stainless cast iron (Ni-Resist) alloy with a magnetic permeability below 1.05.

The mechanical properties should be equivbalent to AISI316 and the casting will be used in sea water.

Thanks for any help,

 

[GRoberts]

316 (A352 CF3M) can be cast with high nickel and nitrogen to acheive <1.05 permeability. However, it is not the best choice for seawater. A352 CK-3MCuN (254SMO) would definately be a better choice for seawater, and although I haven't seen its permeability measured, I know it shows up with 0 FN on a fischer ferritscope.

 

[gieter]

We have had some experience in the past with Ni-Resist (I believe D2C). From what I was told the castings had to be completely machined or ground after heat treatment (900°C+air cooling). If this was not done, the low permeability was not attained.
This contradicts with publications I found stating that machining will induce cold work and thus the formation of martensite. This would raise permeability. It also contradicts with a publication stating that a solution annealing lowers permeability.

Unfortunately 254SMO is not an option due to price issues.

If we only consider CF-3M/CF-8M or Ni-Resist, what would be best?

 

[GRoberts]

I don't have any experience with cast iron at all, but if you post a question about corrosion resistance in the corrosion engineering forum, they might be able to give you an idea of which would last longer in seawater.

 

[arunmrao]

We have used castings in CF 8M successfully in sea water applications. These were placed in water for periods extending over 1 year and no trace of corrosion was noticed. CF8 M offers a cost effective solution .