ΔE 22.8, loose: different enough that you should pick on purpose. Celestial Violet is a little lighter, much more saturated than Tarnished Steel.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Celestial Violet is a little lighter, much more saturated than Tarnished Steel.
The same difference applies the other way round: Tarnished Steel is a little darker, much more muted.
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 Tarnished Steel on the colour wheel See Celestial Violet on the colour wheel
All matches: Tarnished Steel equivalents · Celestial Violet equivalents