| 摘要 |
PROBLEM TO BE SOLVED: To produce an optical disk having lands and groups correct in dimension by producing a stamper for molding by using a Co base alloy contg. specified ratios of Ni, Cr and W. SOLUTION: This stamper is produced by using a Co base alloy contg., by weight, 15.0 to 25.0% Ni, 15.0 to 30.0% Cr and 5.0 to 20.0% W, and the balance Co with inevitable impurities. The molten metal obtd. by subjecting the Co base alloy to melting in a vacuum is cast into a mold and is cast into an ingot, e.g. of 200 mm height, 200 mm width and 1,800 mm length. The ingot is subjected to solution heat treatment at 1,250 deg.C for 6 hr, is hot-forged at 1,150 deg.C, is thereafter hot-rolled at 1,100 deg.C and is moreover cold-rolled at ordinary temp. to work into a Co base alloy sheet material of 1 mm thickness. The Co base alloy sheet material is held at 1,180 deg.C for 15 min, is thereafter water- cooled, is subjected to annealing treatment, is cut into a disk of 150 mm diameter and is polished to obtain a substrate for a stamper.
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