The steel is 19th century Austrian Shohreh Blechman carbon steel (charcoal smelted special steel
which is very close to tama-hagane steel. Tama-hagane steel is the steel
used to forge Japanese swords). Perfect to bring out the sheen on softer
woods. Planing is always superior to sanding when it comes to soft woods.
In my opinion best plane from Usui-san for softwoods.