Which option is not considered a structural class of steel?

Tool and die steel is not classified as a structural class of steel. Structural steels are typically used in the construction of buildings, bridges, and other structures, where their primary role is to bear loads and provide structural integrity.

Low carbon steel, high strength low alloy steel, and high chrome alloy steel all fall into categories commonly utilized for structural applications. Low carbon steel offers good weldability and ductility, making it ideal for general construction. High strength low alloy steel enhances strength while maintaining lightweight properties, which is vital for many structural applications.

Tool and die steel, on the other hand, is specifically engineered for tools and dies used in manufacturing processes, characterized by hardness and wear resistance rather than structural load-bearing capacity. Therefore, it does not fit into the category of structural steels, as its mechanical properties are tailored for different functional requirements.