Metal gasket and production method therefor

A metal gasket consisting of, in terms of % by mass, C:

• 0.10% or less, Si:
• 1.0% or less, Mn:
• 2.0% or less, P:
• 0.04% or less, S:
• 0.01% or less, Ni:
• 25.0% to 60.0%, Cr:
• 10.0% to 20.0%, one or both of Mo and W satisfying Mo+W/2:
• 0.05% to 5.0%, Al:
• 1.6% to 3.0%, Ti:
• 1.5% to 3.0%, Nb:
• 0.3% to 2.5%, V:
• 1.0% or less, B:
• 0.001% to 0.015%, Mg:
• 0.0005% to 0.01%, wherein S/Mg:
• 1.0 or less, N:
• 0.01% or less, O:
• 0.005% or less, and a remainder consisting of Fe and unavoidable impurities,
• wherein the metal gasket has a metal structure having an austenite matrix,
• wherein either:
• a precipitate γ′ phase is not present in the austenite matrix;
• or,
• if a precipitate γ′ phase is present in the austenite matrix, the precipitate γ′ phase present in the austenite matrix has an average equivalent circle diameter smaller than 25 nm,
• wherein the precipitate γ′ phase consists of constituent elements selected from the group consisting of Ni, Al, Ti, and Nb, and
• wherein the metal gasket has a thickness of 1 mm or less.