Patent ID: 7833362

Claim:
A method for improving creep resistance and low cycle fatigue properties of a pressure-containing component that is located between a compressor section and a turbine section of a gas turbine, has been cast from a conventional ductile iron alloy containing, by weight, at least 3% carbon, up to about 2.5% silicon, and up to 0.08% phosphorus, the balance iron and incidental impurities, and is subject to creep and low cycle fatigue when installed in the gas turbine, the method comprising: modifying the ductile iron alloy to additionally contain molybdenum and permit an increased silicon content wherein the modified ductile iron alloy consists of, by weight, about at least 3% carbon, up to 2.75% silicon, 0.4 to 0.8% molybdenum, and the balance of the modified ductile iron alloy is iron and incidental impurities of, by weight, up to 0.11% manganese, up to 0.1% chromium, up to about 0.05% magnesium, up to 0.08% phosphorus, and up to 0.01% sulfur; producing a casting of the modified ductile iron alloy; and then performing a heat treatment process by annealing the casting at a temperature of at least 725° C. for not less than five hours to eliminate carbides and/or stabilize pearlite in the casting; wherein the heat-treated casting of the modified ductile iron alloy exhibits improved creep resistance and low cycle fatigue properties in comparison to an identical casting of the conventional ductile iron alloy.