"It all depends." See if you can find a copy of "Tool Steel Simplified," put out by the Carpenter Steel Company. I'm virtually certain it's out of print, but used copies are around. It will explain the "it all depends" a lot better than I can.
Since I assume the sheetmetal being stamped is pretty mild stuff, I doubt you need the dies too hard. I know almost nothing about die design though.
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Law of Logical Argument - Anything is possible if you don't know what you are talking about.