Inconel 718 has material properties that make it very well-suited for high-temperature springs. It maintains its strength at temperatures in excess of 1,000°F as well or better than any high nickel material on the market. However, there are several factors to consider when choosing an Inconel material for your spring application.
The type of spring you use will help with your decision. Inconel 718 is typically available only in annealed sheet or bar form. If you are using a flat spring at these elevated temperatures, Inconel 718 is generally going to be the right choice. If your spring is a compression spring or extension spring using round wire, Inconel X750 might be the best choice because it is much more available as a wire product than 718. It can be used at temperatures in excess of 1,200°F if it is properly sized and designed for the application. There is even a special heat-treat cycle for the X750 which can help with these applications, though it is costly and time-consuming to perform.
Another thing to consider is the volume of springs required in your production. If you are designing for a large production volume and have the time and budget for having spring wire custom-drawn, then Inconel 718 can be made into spring-tempered wire without a large impact. If your needs are for short-run, small-batch orders of round wire springs, then the readily available sizes of Inconel X750 should be considered since there are a number of wire vendors that stock it.