About locking discussion forums and topics
Locking a topic prevents users from creating new posts or modifying existing posts, making the conversation read only. Users with permission can modify the contents of a locked topic. Locking a topic is an effective way of closing a conversation while allowing users to refer back to posts. Consider locking a topic to end a conversation, then using a pinned summary post inside the topic. When users access the topic, your summary appears at the top.
You can specify start and end dates for when a forum or topic unlocks so you can set things up ahead of time to match your course’s calendar.