| 摘要 |
PURPOSE:To obtain the titled mold member, having excellent durability as well as long life and capable of readily providing optical elements of high accuracy, by forming boride layers on the molding surface layers of base materials consisting of Mo, W or Ta. CONSTITUTION:A dense sintered material of Mo, W or Ta having no bore on the surface is cut to provide mold base materials 3 and 4. The molding surface (3a) and (4a) thereof corresponding to optical surfaces of optical elements are machined to a desired surface accuracy. The resultant mold base materials 3 and 4 are then dipped in a treating bath 53 containing a salt bath agent 53 consisting of boric acid, potassium borate, NaF, K2CO3 and Mg powder and heated by a heater 55 to stick the salt bath agent 53 to at least the molding surfaces (3a) and (4a) of the mold base materials 3 and 4. The surfaces are then lightly ground to form a boride layer 57 on the surface layer part of the resultant base material 56.
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