Why do steel strips and rails lying in warehouses become magnetized after a while?

The planet Earth is characterized by a phenomenon like a magnetic field. The rails are steel, they contain a large amount of iron. After getting acquainted with the school physics course, we know that iron is a ferromagnet. What it is? These are bodies that enhance the induction of the magnetic field. Plus, these bodies over time have their own property – the property of magnetization. Magnetization takes place in the direction of the magnetic field induction. That is, as the current flows on the Earth, so it flows in the rails.