High-Speed Steel (HSS) vs Shirogami #1

Originally developed for machining applications, HSS (notably M2) has found its way into a niche of Japanese woodworking tools — particularly router bits, drill bits, and some specialty plane blades. Its extraordinary hot-hardness is irrelevant for woodworking, but its fine carbide structure and wear resistance make it compelling for specific applications where conventional carbon steel wears prematurely.

Pure high-carbon steel with minimal impurities. Takes a laser-like edge and is easy to sharpen, but more brittle than Aogami. The traditional choice of master woodworkers who demand the finest possible cutting edge and sharpen their tools with religious dedication. Rust forms overnight if neglected.