Where do knife steels come from?

[EOU]

Thank you very much Scott. We're learning although slowly. So I think that we read earlier in this thread that the potential HRC on this powder material (SV30) is in the 60-62 range. Does that mean approximately the same for sintered? Here's where we're going next with this question assuming that the answer is in the affirmative. John Lucas mentioned ( in one of his wood working posts here or emails) that he had done some work with sintered hand plane blades. He commented that they had arrived quite sharp, were very durable edges, but were extremely difficult to re-sharpen. Does this seem to follow? If so, why would they be so difficult to sharpen?