Ni-base alloy, heat-resistant spring made of the alloy, and process for producing the spring

A process for producing a heat-resistant spring comprising the steps of:

• performing solution treatment to a rod or plate made of a Ni-base alloy, the Ni-base alloy consisting of comprising 0.01 to 0.15 mass % of C, 2.0 mass % or less of Si, 2.5 mass % or less of Mn, 12 to 25 mass % of Cr, 5.0 mass % or less of Mo and/or 5.0 mass % or less of W on condition that Mo+W/2 be 5.0 mass % or less, 1.5 to 3.5 mass % of Ti, 0.7 to 2.5 mass % of Al, 20 mass % or less of Fe, a ratio of Ti/Al in terms of atomic percentage ranging from 0.6 to 1.5, and a total content of Ti and Al ranging from 4.0 to 8.5 atomic %:
• subjecting the rod or plate, on which the solution treatment has been performed, to cold working with a reduction ratio of 20% or more to form the rod or plate into a predetermined shape;
• and
• aging the rod or plate member at a temperature of 600 to 900° C. for 0.5 to 24 hours.