If you have a proper antifreeze mixture in the engine block and radiator then it would usually have to get way below 0 for the engine block to freeze.
But if you have just water in the engine block or not the proper antifreeze mixture in the engine and radiator then the engine block could freeze and crack as 32 F.
The coolant or antifreeze in the engine can still freeze at around 30 F or below but still may not be cold enough to freeze the engine block.
The antifreeze may turn to slush but it will warm back up again when you start the engine.