While 1045 carbon steel can be used for a katana, it is not typically regarded as the optimal choice for high-quality or functional katana blades. 1045 is a medium-carbon steel with a carbon content around 0.45%, which places it in the lower range of carbon content for sword-making steels.

Here are a few considerations regarding 1045 carbon steel for a katana:

1. Hardness and Edge Retention: 1045 steel can achieve a moderate level of hardness when properly heat-treated, but it is not as hard as higher carbon steels commonly used for katana blades. This means the blade may not hold an edge as well and may require more frequent sharpening.
2. Toughness: 1045 steel offers decent toughness, allowing the blade to withstand impact to some extent. However, compared to higher carbon steels, it may be more prone to chipping or bending under heavy stress or abuse.
3. Flexibility: 1045 steel provides a moderate level of flexibility, which is important for a sword blade to absorb and distribute forces without breaking. However, it may not have the optimal balance of hardness and flexibility found in dedicated katana steels.
4. Authenticity and Performance: Traditional Japanese katana blades are typically made from specific steels such as tamahagane or other high-carbon steels, which offer superior performance, edge retention, and overall authenticity. 1045 steel may not provide the same level of authenticity or cutting performance as those traditional materials.

While 1045 carbon steel can be used to create a functional katana blade, it is often considered more suitable for decorative or entry-level swords rather than high-performance blades. If you are looking for a katana with superior cutting ability, durability, and historical accuracy, it is advisable to consider steels specifically developed and widely accepted for katana production, such as different types of high-carbon steels or specialized katana steels like T10 or 1095.