A cobalt base alloy consisting essentially of, in weight percent, about 0.1% to about 0.5% carbon, about 0.3% to about 2.0% silicon, about 0.3% to about 2.0% manganese, about 5.0% to about 15.0% nickel, about 26.0% to about 35.0% chromium, about 3.0% to about 10.0% tungsten, about 0.003% to about 0.1% boron, about 0.01% to about 1.0% titanium, about 0.01% to about 1.0% niobium and optionally about 0.05% to about 1.0% mischmetal and the balance being essentially cobalt together with impurities and incidental elements normally associated with a cobalt base alloy, which has high strength and high ductility even at high temperatures and is especially suitable as a material to be used at high temperatures under high thermal stress, such as a material for a nozzle of a gas turbine engine.