As Scott Grandstaff said, the irons in many of these planes are made of high
speed steel (HSS). This steel is tough stuff. It requires some effort, but it
will take and hold an edge for a long time. I've been told that HSS is the only
plane iron that will hold up to pernambuco, a beautiful but gnarly wood commonly
used for violin bows. All of the "regulars", A2, O1, even D2 and PM-V11 will not
stay sharp when subjected to the microscopic spines of this South American wood
species.
Click on the link to see what pernambuco looks like under a microscope: https://ibb.co/dzoncQ">https://ibb.co/dzoncQ