Has the striking surface of your fire steels been worn away more than 1/4 to 1/2 of an inch in use? Probably not. A common practice when some people heat-treat their strikers is to only quench a little bit of the striker surface. They hold the striker in their water/oil about half way in. This only hardens around 1/4 to 1/2 of an inch into the steel - leaving the back half and rest of the striker soft and less brittle. Once you wear through that hardened part of the striker, you are then into softer steel that is very hard to get sparks from.
But, I suspect that your strikers were CASE HARDENED. They were probably made from low carbon steel, and then the outside surface had carbon added through one of the many case-hardening processes. But this only puts lots of carbon into the very thin outside layer of the steel. That thin layer ends up being only a few thousandths of an inch thick. It doesn't take too much use to wear through it.
A few years ago, a major vendor ended up with a batch of case-hardened strikers. They wore out fairly quickly. I never heard how they corrected the customer problem it created. I only heard from several of those disgruntled customers.
If your strikers were case-hardened, then there is little that can be done to ... rescue them. If they were only hardened on a little bit of the striking surface, then there is a possibility that they could be re-hardened. That is, of course, if they are made from all high carbon steel.
Brittleness is always a problem when you heat-treat high carbon steel. To make a good striker, you need it as hard as you can get it. But that also usually makes it as brittle as it can be. It becomes a bit of a delicate balancing act to get it hard enough to make a good striker, and not being too brittle.
The best "tip" I ever received to help with this came from a knife maker. His "tip" was to thermal cycle the striker after you are done forging it to shape but before your final quench. You heat it up to that non-magnetic point, and then pull it out of the heat and let it air cool until you don't see any color. Then heat up and air cool two more times. Then heat to non-magnetic and quench. This Thermal Cycling removes any internal stress in the metal from the forging process. It also then refines the grain size of the metal molecules - making them smaller, finer, and more even. All this adds up to a less brittle striker that can be heat-treated harder. And the harder it is, the better it sparks.
Of course, you have to start with steel that has a high enough carbon content to begin with. I prefer to work with new steel - avoiding dealing with unknown metal alloys and any cracks/stresses in the steel's past history.
I generally use 1095 carbon steel. I thermal cycle after I finish forging to shape. And I then quench the striker completely in water, swirling it around in the water as it cools. If I have forged out some thin parts on the striker handle, I sometimes then will selective heat back up those thin parts to soften them up and make them less brittle.
In the end, it becomes a matter of personal time and energy whether you try to re-heat-treat your striker, or find a new one. Some people want to do it themselves, and enjoy the challenge of making it work. Every now and then, I have one that will not spark well. I usually will try to heat-treat it one more time. If it still doesn't spark well, it goes in my "scrap" pile or on a "display" board. It isn't worth my time to spend any more time on it, and the final results might still be questionable.
Just my humble thoughts to share. Take them as such.
Mikey - yee ol' grumpy German blacksmith out in the Hinterlands
