Titanium Carbide is obtained after smelting Titanium and Carbon in a furnace. So far, Titanium Carbide has two uses:
Making the strongest pickaxe in the game, the Titanium Pickaxe (Diamond pickaxe and 2 Titanium Carbide bars needed).
Making the grenade launcher, needed to shoot grenades (6 steel bars,1 flint block and 2 titanium carbide bars)
When bought from the item shop, titanium carbide costs 250k.