A method of manufacturing a header and alloy subcriticality extrasuper

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A high temperature, high strength Ni-Co-Cr alloy possessing essentially fissure-free weldability for long-life service at 538° C. to 816° C. contains in % by weight about : 23.5 to 25.5% Cr, 15-22% Co, 1.1 to 2.0% Al, 1.0 to 1.8 % Ti, 0.95 to 2.2% Nb, less than 1.0% Mo, less than 1.0% Mn, less than 0.3% Si, less than 3% Fe, less than 0.3% Ta, less than 0.3% W, 0.005 to 0.08% C, 0.01 to 0.3% Zr, 0.0008 to 0.006% B, up to 0.05% rare earth metals, 0.005% to 0.025% Mg plus optional Ca and the balance Ni including trace additions and impurities. The strength and stability is assured at 760° C. when the Al/Ti ratio is constrained to between 0.95 and 1.25. Further, the sum of Al+Ti is constrained to between 2.25 and 3.0. The upper limits for Nb and Si are defined by the relationship : (% Nb+0.95)+3.32(% Si)<3.16.