Steel on Steel ikon

[Liora]

I have a Centaur exemplar with the Steel hooves ancestry feat and the Titan's Breaker ikon on the hooves. Can I use the
"Steel on Steel" Level 4 feat on them.

Thematically it fits, but RAW, i don't know:

Usage: imbued into a melee weapon ikon or worn ikon made of metal, stone, or a similarly hard material

[NorrKnekten]

Honestly I see no issues with that provided that your GM considers those hooves "Sufficiently hard material"

Its a bit ambigious however with the phrase melee weapon ikon. Which could either be melee-weapon ikon, or melee weapon-ikon. I firmly believe its the latter so as long as your weapon ikon is granting you a melee attack its fine. The confusion likely stems from the fact that weapon ikons can be unarmed attacks and thus arent weapons but are still a melee weapon ikon.

[The Contrarian]

A natural attack is not a weapon.

[Tactical Drongo]

I guess the easiest way to use it actually would be to reflavor some free hand simple d4 weapon as hoof attachment which of course would not really be an advantage for steelhooves
but the contrarian is technically right that unarmed attacks are not weapons

[NorrKnekten]

Absolutely, Unarmed attacks arent weapons, That much is clear.

But your unarmed attack can be your weapon ikon, So hands of the wildling is still a melee weapon ikon when applied to a pair of fists.