5160 carbon steel is a popular and highly regarded steel alloy for various applications, including swordmaking. It is a spring steel alloy that contains approximately 0.60% carbon, along with small amounts of other elements such as manganese, silicon, and chromium. Here are some key characteristics of 5160 carbon steel:

1. Strength and Toughness: 5160 steel is known for its exceptional strength and toughness. It has a high tensile strength, allowing it to withstand significant stress and load without permanent deformation or failure. The combination of strength and toughness makes it well-suited for applications that require durability and resistance to impact or bending.
2. Flexibility: One of the notable properties of 5160 steel is its excellent flexibility or springiness. It can be bent and then return to its original shape without breaking or suffering from significant deformation. This property is advantageous in applications where resilience and resistance to bending or twisting are important, such as sword blades.
3. Shock Absorption: Due to its toughness and flexibility, 5160 steel is known for its ability to absorb and distribute shock or impact energy. This property makes it suitable for applications where resistance to shock or vibration is desired, such as sword blades that may experience impacts during use.
4. Edge Retention: While 5160 steel is not as renowned for its edge retention as higher carbon steels like 1095, it can still achieve and hold a satisfactory edge with proper heat treatment. Regular sharpening and maintenance are necessary to keep the blade in optimal cutting condition.
5. Machinability: 5160 steel is generally considered to have good machinability, meaning it can be easily machined, shaped, and formed into desired parts or components.

It's important to note that the specific properties and performance of 5160 carbon steel can vary depending on the heat treatment, forging process, and overall quality of the steel. Proper heat treatment, including quenching and tempering, is essential to maximize its desired characteristics.

When used for sword blades, 5160 steel is often favored for its combination of strength, flexibility, and shock absorption. However, it's worth considering that the overall quality, craftsmanship, and design of the sword, in addition to the steel used, significantly contribute to its performance and durability.