Yes, a katana can become dull over time or with use. The cutting edge of a katana can wear down or become less sharp due to various factors, including cutting practice, contact with hard objects, or inadequate maintenance. Here are a few reasons why a katana can become dull:

1. Cutting Practice: If a katana is used for cutting practice, such as tameshigiri (test cutting) or target practice, the repeated contact with hard targets can gradually wear down the cutting edge and dull the blade.
2. Wear and Tear: Regular use or contact with hard objects can cause the blade to lose its sharpness over time. Scratches, nicks, or dings can also affect the cutting ability of the blade.
3. Improper Cutting Techniques: Improper cutting techniques, such as striking at inappropriate angles or excessive force, can contribute to dulling the blade. Correct cutting technique, which involves proper alignment and minimal force, helps maintain the sharpness of the blade.
4. Inadequate Maintenance: If a katana is not properly maintained, such as regular cleaning and oiling, it can lead to corrosion, rust, or the accumulation of dirt and debris on the blade, which can affect the sharpness and overall condition of the edge.

When a katana becomes dull, it may require sharpening or honing to restore its cutting edge. This process is typically performed by experienced practitioners or professional swordsmiths who have the necessary skills and tools to sharpen the blade properly. It is important to handle the sharpening process with care to maintain the katana's integrity and ensure its continued functionality.