Structural steel is steel that meets specific strength and formability grades. Formability is expressed as elongation after interruption of the tensile test. Structural steel is generally used for load-bearing purposes, where the strength of the steel is an important design criterion.

Structural steel can be subdivided into: carbon structural steel, high-quality carbon structural steel, low-alloy high-strength structural steel, alloy structural steel, spring steel, weather-resistant structural steel, chip-friendly structural steel, non-quenched and tempered mechanical structural steel, etc.

Compared with ordinary carbon structural steel, high-quality carbon structural steel contains lower sulfur, phosphorus and other non-metal inclusion content.

Due to its appropriate hardenability, alloy structural steel has a microstructure of uniform sorbite, bainite or extremely fine pearlite after appropriate metal heat treatment, so it has high tensile strength and yield ratio. (generally around 0.85), with higher toughness and fatigue strength, and lower toughness-brittleness transition temperature, it can be used to manufacture machine parts with larger cross-section sizes.