Crushing iron bones might be prohibitively expensive in terms of
animal's metabolic needs.
Alexander has a valid point. Creatures don't evolve to be cool, they evolve to be effective. Wasting energy on crushing ridiculously strong bones when the rest of the animal's flesh is still (presumably) soft or relatively soft is a bad adaption.
You did not tag your question with reality-check or science-based, so I don't know how interested you are in more practical solutions to this problem. But here are some other options.
If you want the predator to be effective at disabling movement:
Hamstring the enemy instead. Bones need muscles and tendons to move, so if you slice them the appendage won't move at all. This kind of mimics breaking bones in terms of the immobility. For this, the predator just needs razor sharp teeth with a long angled edge for biting and slicing. There are a lot of opportunities here for wonky and scary looking alien predators that retain function. For example long blade like chins, teeth, etc.
If you want the predator to be effective:
Make your predators bite and run predators. There is a precedent for this in terms of Cookie Cutter Sharks.
Cookiecutter Sharks, bite off bits of whale blubber rather than
attempt to kill the whale - which works out much better as the sharks
are significantly smaller than the whales.
Thanks @Morgen for this information.
Instead of outright killing prey your animals can just run up to their targets, take one big meaty bite out of them and then run away with a mouthful. This seems very practical in a scenario where prey has iron bones.
A further look into breaking bones:
Breaking iron bones poses a lot of other challenges too. Drawbacks that effect the predator immediately after it succeeds. Remember that carbonized iron is very brittle and very strong, so:
Breaking carbonized iron requires a lot of force but when it does break it will splinter and its shards will fly everywhere like a small shrapnel grenade. So a big problem here is that if the predator's mouth is not also heavily reinforced, cracking a bone might mean instant death as shard of very sharp carbonized iron fly straight into its head/throat/etc from inside its mouth.
After cracking the carbonized iron, at least some of the very sharp shards are going to be swallowed and have to pass through the predator's body. The inside of an animal is generally not very tough, so this is another good way to die; via massive internal trauma/bleeding. So an extremely reinforced digestive system will also be required, or else very powerful digestive acid to break the iron down in the stomach.
In the end the adaption would require a lot of other complimentary adaptions as well.