So what should be done after the hammer becomes rusty? There are generally two methods of physical rust removal and chemical rust removal. Physical rust removal includes sandblasting, shot blasting, wire brushes, scouring pads, sandpaper, files and other tools, and electric or manual removal of rust on the surface of the object.
Chemical rust removal is done by pickling, which is to soak the rusty object in a pickling tank and remove the rust on the surface of the object through a chemical reaction. If you only have one or a few hammers, use a scouring pad manually. A wire brush attached to an angle grinder or sandpaper will do.