So you got the first one, eh.?!
Always get to try Mark's new toys first...
Anyhow, I am no metallurgist, but it has been of my understanding that (H)
teels are designed to retain their hardness while enduring the high heat generated by high speed tooling... thus the moniker. High speed & high heat are one in the same.
It has also been of my understanding that R2 [steel] produced by Kobelco is simply renamed as SG-2 when Takefu processes it... same PM HSS, different source.
I would not be one to argue that R2/SG2 is on par w/ZDP189, as I have neither used nor sharpened either, but there are many of whom would... obviously, Mr. Itou and all that follow him.
As for the HAP40... I guess you're gonna have a full report real soon.
I was reading it is manufactured by sintering 6 micron powder to keep the steel grain nice & small like our stones like it.