Unfortunately, I do not have a copy of this BS specification. Can you please provide the chemical composition, as well as the strength/hardness requirements? My first impression is that you do want to change to a Ni or Co-based alloy because the wear resistance will be greatly inferior to that of a nitrided steel alloy. Can you provide some additional details, such as your reasoning for changing to Ni or Co-based alloys? Expected operating environment, etc.?