You have to view the flint as a "consumable supply". The edges just dull in use.
What you are doing is using a sharp edge on the flint to dig/chip out little bits of the steel striker. The energy put in to digging/chipping out those small bits of steel heats them up to the point that the carbon in the steel burns - that's the sparks you see. The harder the steel is, the easier it is to dig/chip out small bits of the steel. The softer the steel is, the larger the bits of steel are and the harder it is to chip them out. Larger bits of steel means it is harder to get them hot enough for the carbon to burn. Also, the softer your steel is, the more it will "grab" your flint. The steel will want to dig out in bigger chunks and/or shavings - instead of crumbling/chipping out in small bits.
So it all ends up being a balancing trick when you heat-treat a striker. The harder you heat-treat it, the easier it is to chip out smaller bits of steel and get better sparks. But that makes the whole steel much more brittle, and subject to breaking. The softer you heat-treat your striker, or temper it back, the less brittle it is. But that makes it much harder to strike good sparks. Your flint wants to dig in too much, and chip out chunks of steel too large to burn well. As I said, a tricky balancing act to heat-treat correctly. The best sparks come from a striker heat-treated very hard. But that makes it more brittle and subject to breakage.
In my experience, a too-soft striker tends to chew up the flint edges faster. The steel tends to "grab" the flint more, and the flint tends to dig in farther. All this just puts more pressure and wear on the flint's sharp edges.
Using a larger chunk of flint does help some people. That larger chunk offers more internal support for the edges on it. But, in the end, the flint just gets "consumed" - however long or short of time it takes.
A well documented source of flint to use is gun flints. They were often shipped/sold together. They work just as well as larger chards - once you get adjusted to using them. And gun flints are available from many sources.
Just my humble thoughts to share. Take them as such.
yhs
Mike Ameling
