Process for the manufacture of a watch case with a visible highly invariable surface

Claim 1

Process for the manufacture of a watch case or like workpiece having a surface highly resistant to wear and corrosion, said surface having a hardness of at least 1300 kp/mm 2 , comprising the steps of; a. pressing and sintering a powdered metal mixture comprising at least one base powdered metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, in admixture with at least one binder powdered metal selected from the group consisting of copper, silver, gold, iron, cobalt, nickel, ruthenium, rhodium, palladium, ormium, iridium and platinum, the proportion of said binder metal in said mixture being not more than about 15% of the total weight, at a temperature between about 1400° and about 1500° C to produce a substantially poreless unfinished workpiece; b. forming said unfinished workpiece into finished shape by cutting and milling, and polishing the faces thereof; c. subjecting the finished workpiece formed in step (b) to a surface hardening treatment at a temperature of about 950° C to transform at least a part of the metal in the surface to borides, carbides, or nitrides;