ELINVAR
Elinvar is a steel alloy (iron, carbon, nickel) patented by Charles-Edouard Guillaume, designed to combine elastic properties with a very low coefficient of thermal expansion (hence elastic and invariable). This discovery earned the physicist from Fleurier the Nobel Prize in Physics in 1920. Elinvar is still widely used today for manufacturing steel hairsprings.
Useful link:
– Steels