Again,
I'm not saying that 5160 is a bad steel. I'm just saying it is more brittle then 1045. And nobody has proven otherwise. Let me clarify:
5160 =
0,55-0,65 % Carbon
0,75-1% Manganese
0,7 - 0,9 % Chromium
The rest is Fe or just Iron
1045 =
0,43-0,5 % Carbon
0,6 - 0,9 % Manganese
0 - 0,04 % Phosphorus
0- 0,05 % Sulfur
The rest is Fe or just Iron
As Sulfur and Phosphorus can be in 1045 but do not have to be, I'm going to disregard them for this instance. That leaves Carbon (used to actually harden the blade) and Manganese (do desolve oxigen). The main difference is the chromium content. If you realy want to knit pick, just look up 1060. They're practically the same in content except Chromium.
Now lets look up the elemental properties of the materials used and especially the Mohl scale to keep it fairly simple.
Iron:
https://en.wikipedia.org/wiki/Iron
Mohls hardness: 4 .
See it as the base hardness of the material. The only difference being Chromium between the 2.
Chromium:
https://en.wikipedia.org/wiki/Chromium
Mohls hardness : 8,5 .
Thats the added hardness and brittleness found with adding Chromium. The higher the chromium content, the harder and more brittle it becomes.
A more simple way to look at Chrome is looked at a chromed bumper. It the stuff on top of the shiny nickel plated bit with the blueish tint. It chips of when you whack it with a hammer. The rest of the metal just bends. The same properties I am talking about the whole time.
I work with a lot of metals as an engineer, so I need to know mechanical properties. And trust me on this one: The enviroment I'm talking about is lot harder on the metals compaired to any axe or a knife will ever experience: Engines, cars and planes. There is a shit ton more stress involved and far higher operating temps.
And I'm not saying that it will shatter upon impact. As I said from the beginning: It depends on the temper of the steel itself applied by the smith. But as a base its a step in the wrong direction for anything that has an impact sensitive job. It may not even crack during the lifetime you use a tool. But it will crack sooner then 1045 steel if all else is kept equal. Thats all I'm saying.... It's highly likely that won't notice the difference though: because everything else isn't kept equal in real life. Temper differs from axe to axe, steel differs from batch to batch (remember each category has a minimum and maximum content), force differs from user to user and from job to job.
And lets not forget one thing: Allmost all steel is recycled steel. So getting the purest grades becomes harder and harder (and therefore more expensive). But each and every steel has it minimum en maximum content for it to be called said steel.
1045 is more expensive over here compaired to 5160 in Europe. How about in the US or Canada? And thats not saying anything about quality, but everything about it being harder to produce.
Lets not forget that marketing is the name of the game these days. Its not about getting the best product. That died during the early 20th century. Its about creating a need that you want....