When steel is heated above its Curie temperature, it undergoes a phase change that causes it to lose its magnetic properties. The Curie temperature is the specific temperature at which a ferromagnetic material, such as steel, transitions from a ferromagnetic state to a paramagnetic state. In the paramagnetic state, the material does not exhibit strong magnetic behavior.
If steel is heated above its Curie temperature and then allowed to cool, it will regain its magnetic properties as it transitions back to the ferromagnetic state. The cooling process does not permanently eliminate the magnetic properties of the steel.
To maintain the demagnetized state, additional steps need to be taken after heating the steel above its Curie temperature. One common method is to cool the steel in the presence of a magnetic field. This process is known as "annealing in a magnetic field." By cooling the steel while subjected to a magnetic field, the material aligns its magnetic domains in the desired orientation, resulting in a demagnetized state that persists even after the cooling process.
So, without specific measures like cooling in a magnetic field, steel heated above its Curie temperature will regain its magnetic properties upon cooling.