Need a bit more specific info.
a) Does the mechanical steering lock, operated by the key, engage?
Or, b) is it the electric power steering going stiff?
a) You will need a new lock mechanism, NOW, before it locks up and you crash. As this is the mechanical bit, one from a breaker might do if you can swap the lock barrel over and retain your original key.
b) A common failure mode. Will need your steering unit reconditioned.