Sacrificial Steel is additive with similar mods. For example, a Galatine with a max rank Sacrificial Steel (full set bonus) and True Punishment will have a 10% × (1 + 110% + 40%) = 25% critical chance.
This mod is given at the penultimate mission of The Sacrifice, automatically ranked to level 5.
Sacrificial Steel is essentially the True Steel mod with Legendary rarity and 5 more ranks. It is considered the same mod as its Common counterpart, and thus both mods cannot be equipped together.
The set bonus for Sacrificial Steel increases all stats given by the mod by 25% of mod's value per set pieces. At max rank with full set bonus, Sacrificial Steel grants a critical bonus of +110% and a damage bonus of +41.3% against Sentients.
This mod is equal to True Steel at rank 5 when using 2 set pieces. It outperforms at rank 7 alone or rank 6 when using 2 set pieces.
To (re-)add an polarity to a mod slot, an Umbra Forma which is only currently obtainable once from Nightwave is required, so it's advised not to overwrite a pre-existing one.
Similar to other faction damage mods (i.e. Smite Grineer), the bonus damage against Sentients gets applied on top of the base damage and any added elemental damage of the equipped melee weapon (see Damage for complete mechanics).