Sure makes it a good anti rotation shaft! Not what you are looking for. The Thompson hardened shafting is the only way. As I remember the core of the shaft is usually not hardened, not real soft but you can drill and tap.
Regarding my suggestion about the Gibbs Oil, I have a collection of very old machinist measuring tools, dividers, compass's , inside and out side dividers etc. When I got them they were pretty corroded and hard or impossible to adjust. I cleaned them up real good and them soaked them in Gibbs oil for about a week. They have been hanging above my lathe for 5 years through summer heat, winter cold and rain and no rust. Good stuff.
Rex