All my puukkos have a Lauri edge-hardened blade, which is a modern version of a traditional puukko blade. In the old days, Finnish blacksmiths hardened the blade with a furnace fire, we use electricity (induction current). I have developed the hardening process with Lauri. We use 80CrV2 steel, which is like carbon steel, but small amounts of Cr and V make heat treatment easier. In our edge-hardening process, the starting condition is spring-hardened (50 HRC) or normalized (34 HRC) steel. When spring-hardened, we speak about double-hardening because the edge-hardening is a second hardening. The hardened zone is about 6-7 mm wide and has a hardness of 62-63 HRC. So, the edge cuts wildly while the softer back prevents breaking off. The spring-hardened back is stronger, while the normalized back is more traditional.