Method of lowering permeability of difficult-to-work Co alloy

A method of lowering the permeability of a difficult-to-work Co alloy, which comprises:

• a) preparing a Co alloy by melting, said Co alloy comprising:
• i) 4 to 25 atomic % of Cr;
• and
• ii) 0.5 to 10 atomic % of one or more elements selected from the group consisting of Ta, Mo, W, V, Nb, Hf, Zr, Ti and B, with the proviso that the upper limit of B is 5 atomic %, the balance being 50 atomic % or more of Co and inevitable impurities;
• b) preparing a sheet-shaped ingot having a thickness of 30 mm or less using said Co alloy;
• and
• c) covering the surface of said ingot with a metal capsule or coating said ingot with a glass lubricant, and hot-rolling and performing reduction of said ingot at least twice, with re-heating therebetween, whereby an entire reduction of 30% or more is obtained.

A method of lowering the permeability of a difficult-to-work Co alloy, comprising:

• a) 0.1 to 40 atomic % of Ni or 0.1 to 40 atomic % of Pt, or both;
• i) 4 to 25 atomic % of Cr;
• and
• ii) 0.5 to 10 atomic % of one or more elements selected from the group consisting of Ta, Mo, W, V, Nb, Hf, Zr, Ti and B, with the proviso that the upper limit of B is 5 atomic %, the balance being 50 atomic % or more of Co and inevitable impurities;
• b) preparing a sheet-shaped ingot having a thickness of 30 mm or less using said Co alloy;
• and
• c) covering the surface of said ingot with a metal capsule or coating said ingot with a glass lubricant, and hot-rolling and performing reduction of said ingot at least twice, with re-heating therebetween, whereby an entire reduction of 30% or more is obtained.