Its going to depend on the flintlock, of course. Some have only Case-hardened frizzens. You eventually can cut through that thin case, and will have to have it rehardened. Companies are getting away from Case hardening frizzens, because of all the complaints they are receiving from customers. They are using steels with higher amounts of carbon to cast these parts, and the result is a frizzen that is hardened completely through the body. Tempering the frizzen makes a tough hard surface with plenty of carbon to create sparks.
DO check the pivot Screw/pin for smoothness. It should feel like glass when you remove the frizzen spring, and then rotate the frizzen on the pivot manually. If not, polish it with fine emery cloth, until it is smooth as glass to your touch. A small, jeweler's Rattail file can be used to take any burrs out of the hole through the frizzen for the pivot screw/pin. Then curl up a strip of emery cloth to fit into the hole, and twist it around many times to polish the inside of the hole, too. Once polished, all you need to do is oil it every time you clean the gun.
As to the face of the frizzen, IF your flint is striking the frizzen at a very square angle, its going to be gouging divots into the face. The ruts created will soon become a washboard, breaking off large chunks of your flint, and preventing the sparks that are produced from being thrown down into the flashpan. Instead, they will go all over. The best mainenance for the face of the frizzen is to adjust the angle of impact of the flint to the frizzen so that its 60 degrees, and strikes about 2/3 the way UP from the bottom of the frizzen. With that angle, you will see a scraping of the face, and only at the initial point of impact will you see some pits where irregular edges on the flint dig into the steel.
Depending on how often you shoot the gun, when these pits begin to bother you, take some emery cloth, or a sanding disc on a dremel tool, and polish the face again. Because flint is NOT a totally homogeneous substance, its impossible to prevent all holes in the face. That edge is going to break off along lines reflected in its molecular structure, and if there is something inside the flint that interrupts the line of cleavage, you are going to have a small irregularity in the edge. It may not be large enough to spot even with a physical examination of the flint edge between shots.
I can tell you that the smoother the face of the frizzen is, the easier it is for the full width of your flint to cut steel from it, just like a hot wire slicing through soft cheese. But, with use, imperfections in the steel, and irregularities in the flint are going to give you some pits, no matter what you do. Periodic checks of the face are part of normal maintenance. When in doubt, polish it!
You can case harden your own frizzen, using Casenit. There are several recent threads here on the forum, under the Gun Builder's Bench, explaining how to do this properly. If you have a frizzen that is only case-hardened, you might want to look around for a better steel frizzen, that can be hardened once, and then forgotten about. There are recent posts explaining how to harden and temper a frizzen properly, too.