Don't forget the difference between a prototype and a one-off and something you will be using 50 times a day every day for years!
In general coil and leaf springs are a decent tool for tooling. For specific tools that will need to hold a shape when burried in hot steel high alloyed (expensive) steel may really be the best way to go.
My hardy is the broken off end of a jackhammer bit forged down to fit through the hardy hole and forged thinner towards the edge. Made it close to 20 years ago and it's still going strong---though I prefer it softer than the hammer face as it's simpler to dress when one of my students messes it up.
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Thomas
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