SUS 440C electropolishing

I'm having some problem doing electropolish for sus 440c. The colour turn out to be grey but I need shining surface since the part is used in clean room. Kindly give me some advice.

Below is some technical information about the part:

Material : SUS 440C
Process : machining ( turning ) > Vacuum hardening > electropolish.

Hello Philip!

It's going to be rather difficult to get a bright shiny electropolished surface on standard 440C stainless steel. 440C is a bearing grade, and has a large number of fine chromium carbides throughout the matrix of the metal. The gray you see is likely due to the scattering of the light at the not-so-very-smooth surface.

There are grades of 440C that are made by powder metallurgy methods: at least CarTech and Crucible in the States make them, and there are likely Asian suppliers as well. The far finer carbide size of these grades makes them useful in low-noise bearings, and perhaps for your application as well.

Good luck!