Why are different metals sometimes added to molten carbon steels?

Different metals are added into molten steel in order to form different alloys of steel having different properties for instance zinc or vanadium are added to get stainless steel which does not corrode.

The sun is already about 4.5 billion years old, it is expected that in about another 4.5 billion years it will consume all its hydrogen and expand to form a red giant, after that it will burn iron for about another billion years and convert into a white dwarf so i'd say it is an insanely long time.