I am looking for a non-ferromagnetic, maybe a steel type and brazeable material which has an expansion coefficient in an order of magnitude of 8-15ppm/K from 20°C to 800°C , as mean value, would be ideal. Has anybody any ideas?
If you are looking for a very low coefficient of thermal expansion, try Invar (trademark). It was designed for this very purpose. It has a coefficient of 1.7-2.0 from 20-90C.
Thank you for your help. The material I chose finally was Inconel 600. It was the nearest fit with a mean expansion coefficient of about 15 between 20 and 800°C. It was the best fit I could get for my requirements.