Wesley: Those are a lot of questions. With regard to the 440C vs. 420SS issue, provided that the quenching process produced >90% martensite, then 440C would have a higher hardness than 420SS and should hold an edge better, based on the higher hardness. The sub-zero quench is to transform untransformed austenite to martensite and can be applied to both 440 and 420. With regards to breaking, at equivalent hardness levels, both should possess equal resistance (or susceptibility) to fracture. D2 is not commonly used for knife blades probably based on their greater material cost and difficulty of fabrication as compared with the martensitic stainless steels. The other questions, we cannot answer with confidence. Hope this helps! David Hendrix The Hendrix Group Inc.