The problem could be also the duplex 22005 if the chloride are too high..at 65°C there is some risck of pitting or SCC
What kind of service is ? Oil&Gas?
Mechanical strength is what you're after here. Your carbon steel part will be freely corroding in services where 31803 is properly specified, so this must be some kind of secondary attachment or spec break connection where the corrosion conditions are not severe.
If it's a connection to a structure outside the corrosion zone, consider the use of a "poison pad" between the CS and the 31803 so the base metallurgy remains intact.