Patent ID: 8083874

Claim:
A method for producing a forged low thermal expansion Ni-base superalloy with a high creep fracture strength, the superalloy comprising a nickel containing γ′ phase, a nickel containing A 2 B phase and, as a matrix, an austenite phase wherein Ni is the main component and Mo, W and Re are solid-solved therein, and a carbide phase in the form of aggregated carbides on grain boundaries, said method comprising: preparing an alloy comprising, by weight %, C: 0.02 to 0.15%, Si: 1% or less, Mn: 1% or less, Cr: 5 to 20%, at least one of Mo, W and Re, which satisfy the relationship Mo+½(W+Re): 17 to 27%, Al: 0.1 to 1.22%, Ti: 0.1 to 2%, Nb and Ta, which satisfy the relationship Nb+Ta/2: 1.5% or less, Fe: 10% or less, Co: 5% or less, B: 0.001 to 0.02%, Zr: 0.001 to 0.2%, a remainder of Ni and inevitable components; subjecting the alloy to a solution heat treatment under the condition of at a temperature of 1000 to 1200° C.; subjecting the alloy to either a carbide stabilizing treatment to form the aggregated carbides on grain boundaries and to stabilize the aggregated carbides under the conditions of at a temperature of not less than 850° C. and less than 1000° C. and for 1 to 50 hours, or a carbide stabilizing treatment to form the aggregated carbides on grain boundaries to stabilize the aggregated carbides by cooling from the temperature in the solution heat treatment to 850° C. at a cooling rate of 100° C. or less per hour; subjecting the alloy to a first aging treatment to precipitate the γ′ phase under the conditions of at a temperature of 720 to 900° C. and for 1 to 50 hours; and subjecting the alloy to a second aging treatment to precipitate the A 2 B phase under the conditions of at a temperature of 550 to 700° C. and for 5 to 100 hours.