This is thoroughly discussed in the book: "Hydraulic Die Forming for Jewelers and Metalsmiths" by Susan Kingsley and will not be covered here. Suffice it to say that the top plate should be tempered to 650-700 F. Use stainless steel wire to fasten the loose punch to the top plate for ease of handling.

If you choose to heat treat the die, steps #20 and #21 are done during the hinge softening phase. Insert just the tip of the screwdriver into the die and playing a torch on the lower portion of the hinge to reduce hardness in that area and "freeze" the hinge in the open position. This also makes the hinge less stiff.