| 摘要 |
PROBLEM TO BE SOLVED: To obtain a glass forming die without the protective film being released even if glass is repeatedly formed, excellent in durability and suitable to produce an optical lens by a reheat-press process by treating the die in a nitrogen atmosphere and decreasing the nitrogen atom concn. continuously from the die surface toward the inside. SOLUTION: Silicon carbide and sintered hard alloy are optimum as the base material of the die. The die is allowed to stand in the nitrogen atmosphere at 0.7×10<5> -4×10<5> Pa and 1,200-1,800 deg.C for 1-10 hr and heat-treated or treated with the nitrogen plasma of 100-500 W at room temp. to 500 deg.C for 1-5 hr. By such treatment, a part of the outermost surface is converted mainly to silicon nitride when the base material is made of silicon carbide and converted to tungsten nitride when the base material is formed with sintered hard alloy. Consequently, a die capable of being easily released even from glass is obtained.
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