5160 is a high carbon spring steel. It contains a mixture of 'ingredients' that allow it to be hardened in order to keep its edge, as well as retaining amazing flexibility which makes it impossible for it to take a permanent set. This type of steel sacrifices a little in hardenability but makes up for it in toughness and resilience.
It is possible to differentially treat 5160 but of course due to the then differing hardnesses in the steel, it loses its ability to flex in the way it once could. This makes it become functionally very much like a normal high carbon steel.
note: 9260 is incredibly similar to 5160, the main difference being 51xx steels use chromium as their main alloying agent and 92xx uses silicon, but as much as people argue over which is best, both steels seem to be largely comparable as far as performance is concerned.
A table showing the composition of 5160 spring steel
|Iron, Fe||97.085 - 97.84|
|Manganese, Mn||0.750 - 1|
|Chromium, Cr||0.7 - 0.9|
|Carbon, C||0.560 - 0.640|
|Phosphorous, P||≤ 0.0350|
|Silicon, Si||0.150 - 0.3|
|Sulfur, S||≤ 0.04|