ΔE 19.5, loose: different enough that you should pick on purpose. Natural Steel is noticeably darker, much more muted than Cobalt Alchemy.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Natural Steel is noticeably darker, much more muted than Cobalt Alchemy.
The same difference applies the other way round: Cobalt Alchemy is noticeably lighter, much more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Cobalt Alchemy on the colour wheel See Natural Steel on the colour wheel
All matches: Cobalt Alchemy equivalents · Natural Steel equivalents