An alloy contains the following elements, the proportions being indicated as percentage by weight of the alloy (limit values included): Cr 20 to 35%, Fe 0 to 6%, W 3 to 8%, Nb 0.5 to 3%, Ti 0 to 1%, C 0.4 to 1%, Co 0 to 3%, Si 0.1 to 1.5%, Mn 0.1 to 1%, the remainder consisting of nickel and unavoidable impurities.