Cast iron plating problem

I am a production engineer.i have the following question.i have a cast iron component grade 180, this was heat treated to 500 °C for 4 hrs. after this it was machined and then electroless nickel plated.and then final machined to size.the first stage machining was unstable.to solve this problem we increase the iron grade to 250 and heat treated to 800 to 880 deg C.this resulted in a stable machined component.But the electroless nickel plating process became a problem.i do not know the reason for this , Must the casting be sand blasted first before plating or is the plating process a problem due to more carbon as a result of the heat treatment at higher temp? Advice on this process is required.

Dear,

Heat treatment in high temperature may cause a thick layer of black oxide with high carbon content that can't remove with common way in plating. I suggest you should sand blast or shot blast to remove this layer. If the grey iron can be seen it's Ok for plating.