Any steel will flex, it doesn't even have to be a steel that will work for knives to flex. Anything from 52100 down to 1018 will flex, however the hardness level will determine what it will do when it stops flexing. Will it bend or will it break? Untreated 1018 will flex within a certain range until one is tired of flexing it, but if you exceed its narrow flexing range just once it will bend. A fully hardened high carbon steel will flex equally as well over a wider range until you tire of flexing it, but if you exceeds its much wider range just once it will break.
The above paragraph is to illustrate that despite what has been touted, literally for ages, flexibility is actually irrelevant to a large blades function. What is really the key is impact toughness. Here a steel with more than .8% carbon really doesn't offer any advantages in toughness while 1018 would be very tough, but would lack the strength required to keep its shape and do the job. For a machete you would find a nice balancing point from .5% carbon to .8% carbon and any alloying that helps with toughness would be a plus. Alloying such as silicon and nickel will allow you to bump up your hardness to increase strength while still allowing you to maintain toughness; essentially allowing you to have your cake and eat it too.
Kudos and applause to NDallyn,:thumbup: for pointing out the often overlooked factor that is easily as important as the application- what steels are you set up best to work with.
