Am I permitted to conceal the news of my memorization?

The basic principle is that a Muslim should speak about the blessings Allah has bestowed upon him out of gratitude and compliance, as Allah Almighty says: "But as for the favor of your Lord, report [it]." However, there is no harm in concealing some blessings, and the default ruling for this is permissibility. If one fears the evil eye or envy, then it is better to conceal his blessings from those he fears.