OK, well let's be careful about wording before we start. To be non magnetic you need a hairspring that has no ferrous metals in it at all and that realistically means silicon or parachrom. All of the others are magnetic resistant, they can still be magnetised if you try hard enough - stick them in an MRI machine and the rate will be affected. Additionally, these alloys were designed to be less reactive to heat - less expansion and contraction affecting the rate.
Elinvar was the first major step forward from steel and that appeared around 1920 but that was still more than 50% iron. Nivarox came along in the 30s and reduced the iron content to about 5%. Parachrom was the first mass market hairspring to completely eliminate iron - i.e. to be non-magnetic and that appeared in 2000. Nowadays Rolex are movingto the next generation - blue parachrom which is an oxide coated version of the original. It's not just because it looks better, it supposedly makes the parachrom even more stable / less reactive to heat.
Metallurgically the two are vastly different - parachrom is mostly niobium (>80%) with the rest zirconium, nivarox is almost 50% cobalt with chromium, nickel, iron, titanium and beryllium.
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