One of the strongest types of spring steel commonly used is a high-performance alloy called maraging steel. Maraging steel is known for its exceptional strength, toughness, and resistance to deformation.

Here are some key characteristics of maraging steel:

1. High Strength: Maraging steel exhibits an extremely high tensile strength, typically ranging from 1,300 to 2,000 MPa (megapascals). This makes it significantly stronger than most other types of spring steel.
2. Low Carbon Content: Maraging steel has a relatively low carbon content, typically around 0.03% to 0.20%. The low carbon content allows for the formation of intermetallic compounds, contributing to the steel's unique properties.
3. Age Hardening: Maraging steel gains its strength through a process called age hardening or precipitation hardening. This involves subjecting the steel to a specific heat treatment process, which causes the formation of fine, dispersed particles within the steel's microstructure, enhancing its strength and toughness.
4. Toughness and Ductility: Maraging steel exhibits excellent toughness and ductility, allowing it to withstand high levels of stress and deformation without breaking or fracturing.
5. Applications: Due to its exceptional strength, maraging steel is commonly used in demanding applications that require high-performance springs, such as aerospace components, aircraft landing gear, missile systems, and high-end mechanical springs.

It's important to note that maraging steel is a specialized and relatively expensive alloy, primarily used in advanced technological applications that require the utmost strength and reliability. For more common and cost-effective spring steel applications, other high-strength steels such as oil-hardened spring steel (e.g., AISI 6150) or chrome vanadium spring steel (e.g., AISI 9260) are often utilized, offering a good balance between strength, toughness, and cost-effectiveness.