55 HRC is a very high hardness, even for steels.
Ideally the corrosion resistance of the steel would have to match AISI 316L or be even better.
Qenched stainless steel can go to 55HRC. Even to 65 HRC. But this is at the price of a high Carbone content. Carbone react with free Chromium and makes it unavailable for corrosion resistance. So that qenched stainless steel often have a poor corrosion resistance.
The most basic option is AISI 420. It has the minimum amount of Carbone needed and show a relatively good corrosion resistance. It is available at a very good price.
In the other hand we have the Cronidur30/Bohler N360. It is basically like if the 420 had been highly alloyed with everything available. It has 15% Chromium, 1% Molybdenium, 0,4% Nitrogen and some Vanadium. This gives it a really higher corrosion resistance but it actually only poorly match AISI 304, the most basic Austenitic Stainless Steel. It cost something like $30 per Kg. That's 6 time the price of the 420.
Precipitation Hardening stainless steel like 13-8 Mo PH would only reach 45 HRC. That's already high. I'm wondering if there is specific versions that can do better. This type of steel has a better corrosion resistance than quenched steels. I know that Myodo produce a steel called H1 but it is only available in Japan.
There is also some maraging stainless steels that can reach 55HRC. I have no idea of the price and actual corrosion resistance.
Highly strained by cold working classical stainless steel like 301 or Springflex can reach very high hardness. I don't know for what plate thickness 55 HRC could be reached. The other point is that cold working produce Martensite and reduce corrosion resistance. I don't know how good is final corrosion resistance.
I thought about high temperature Nitrocarburation. However this process reduce corrosion resistance. I don't know by what amount.
Another solution is to use a surface treatment like chemical Nickel. However I'm not totally confident in this type of solution because the corrosion resistance is reduced to 0 locally where the coating is breached.
If you have any idea. I would be greatly interested.
Edit : to make it short
I'm looking for a steel that :
is as corrosion resistant as 316L or better
reach a hardness of 55 HRC
The steel will be used in a sort of bearing that is in contact with salty and a bit of citric acidic mixture in an industrial environment.