I doubt case hardening is sufficient. The correct alloy steel heat-treated appropriately will be both hard and tough... I know Stihl's bigger dogs are not just case hardened -they are tough to drill though - all the way...
Lakeside, case hardening would/could easily be sufficient for this application. Case hardening is the cheapest method for mass hardening of sheet steel products, and you could easily case harden steel that is the thickness of the spikes and it would be incredible hard to drill through and very tough.
I seriously doubt they are using an expensive tool steel, and probably not 4140, because they are both relatively expensive compare to case hardening a cheaper steel and I can't think of any benefits they would possess over a case hardened steel in this application. The 4140 could be stamped then conveyored through flames and quenched in water easier than case hardening steel, but against it is a lot more expensive material, than case hardening regular steel, and I would seriously doubt they use 4140.
My opinion, it is a case hardened stamped steel product,
Sam