JD,
Please don't hate me! Seems I'm being argumentative, but there's something I feel the need to explain. Chromioum and other alloys such as nickel and molybdenum are primarily added to low alloy steels for HARDENABILITY. Hardenibility is diffferent than hardness. Hardenability is the ability to produce martensite. Martensite is of course the structrue which is responsible for a piece of steel's hardness after heating and quenching. What the alloying elements such as nickel, chrome and moly do is delay non-martensitic transformations (pearlite, bainite etc). As the section size of a piece of material becomes larger, it becomes more difficult to cool the interior in sufficient time during quenching to obtain a fully hard structure. So in a nutshell, these alloys allow material to be hardened deeper. This isn't necessary in thin sections, but as size increases, it becomes critical.
In the case of the 5160, the .60% nominal carbon is still the primary element that is responsible for the final hardness. The chromioum is primarily present to allow hardness to be obtained at a deeper depths on thicker sections. On thin sections, it's impact would not be significant.
With all this said, material with .60% carbon is pretty low for a frizzen.
