Iron Warriors vs Blackened Steel

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. Blackened Steel is a little lighter, more muted than Iron Warriors.

Can I use Blackened Steel instead of Iron Warriors?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Blackened Steel is a little lighter, more muted than Iron Warriors.

Can I use Iron Warriors instead of Blackened Steel?

The same difference applies the other way round: Iron Warriors is a little darker, 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.