The blades probably don't have any tissues.
I specified they be made of steel
I'm guessing I missed something important.
Either this:
[TISSUE:STEEL]
[TISSUE_NAME:steel(?):steel]
[TISSUE_MATERIAL:INORGANIC:STEEL]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:BLADE:STEEL]
Or this:
[USE_MATERIAL_TEMPLATE:BLADEBONE:BONE_TEMPLATE] - materials based on steel
[STATE_NAME_ADJ:ALL_SOLID:sharp, twisted bone]
[STATE_NAME_ADJ:LIQUID:n/a] - it doesn't melt
[STATE_NAME_ADJ:GAS:n/a] - or turn into gas
<MATERIAL_VALUE:30> - optional
[SOLID_DENSITY:7850]
[LIQUID_DENSITY:6980]
[MOLAR_MASS:55845]
[IMPACT_YIELD:1505000]
[IMPACT_FRACTURE:2520000]
[IMPACT_STRAIN_AT_YIELD:940]
[COMPRESSIVE_YIELD:1505000]
[COMPRESSIVE_FRACTURE:2520000]
[COMPRESSIVE_STRAIN_AT_YIELD:940] 160
[TENSILE_YIELD:430000]
[TENSILE_FRACTURE:720000]
[TENSILE_STRAIN_AT_YIELD:225] 200
[TORSION_YIELD:430000]
[TORSION_FRACTURE:720000]
[TORSION_STRAIN_AT_YIELD:215]
[SHEAR_YIELD:430000]
[SHEAR_FRACTURE:720000]
[SHEAR_STRAIN_AT_YIELD:215] no data, used 200
[BENDING_YIELD:430000]
[BENDING_FRACTURE:720000]
[BENDING_STRAIN_AT_YIELD:215]
[MAX_EDGE:10000]
[TISSUE:BLADEBONE]
[TISSUE_NAME:sharp, twisted bone:NP]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:BLADEBONE]
[TISSUE_MAT_STATE:SOLID]
[STRUCTURAL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:BLADE:BLADEBONE]
The problem with using plain steel is that it will show up as 'necromorph steel' or if the creature has a name, then it will appear as 'Necromorph 1's steel'.
The second one uses pure bone as a base, with a new name and edited material values to match steel. The bone's name will appear as 'necromorph sharp, twisted bone'.
Of course, the bone's material template takes care of the other tags like [ITEMS_HARD] and [ITEMS_BARRED], so you can still carve figurines of necromorphs raping unitarian colonists.
Also, the [TISSUE:BLADEBONE] tissue lacks pain receptors, to remedy that, just add [PAIN_RECEPTORS:XX], where XX stands for numbers. Note that, higher numbers mean it hurts more.