Pressure:
The hardness of steel makes it very slippery. There’s a noticable difference between steel and even the hardest copper you can buy. Steel will tend to slip when applying more pressure to pop a big flake. Although, you can use a mild steel like the ones for horse shoe nails for notching and serrating. This is because steel has the strength to be very thin and not wear down as quickly. The thinness gives you the ability to be very precise.
Percusion:
This is where steel is normally found being used. Small ball peen hammers can be used to quickly flake some tough rock. I’ve also seen people use sledge hammers to spall massive boulders as nothing else besides another really big rock would work.
That’s what I know in a nutshell
